Paul Asimow (PhD '97), Igneous Petrologist and High-Pressure Mineral Physics Experimentalist

As a native of Los Angeles whose family has been here since the 1920s, Paul Asimow recounts with humor that he never heard of Caltech until he went to Harvard as an undergraduate. In the years since, he has more than made up for this understandable oversight: as a graduate student here, Asimow quickly established himself as a vital member of the Division of Geological and Planetary Sciences, where he embraced the faculty tradition of treating graduate students as colleagues. During these years, Asimow gained exposure to, and made advances in, most of the Division's key areas of work, including field geology and thermodynamical work in both an experimental and theoretical context - all at a time when a new generation of high powered computers were revolutionizing possibilities in geology and geophysics.

In the discussions below, Asimow underscores the importance of postdoctoral appointments in the scholarly trajectory of a modern scientific career. At Lamont Earth Observatory at Columbia University, Asimow had the freedom to tie up the loose ends of his dissertation research and gain exposure to new areas of scientific inquiry. For his return to Caltech, this time as a member of the faculty, Asimow had assembled a richly diverse research agenda poised for discovery in a range of topics in igneous petrology. For all his exposure to the diversity of research as a graduate student, one professor he only came to know well upon his return was Tom Ahrens, founder of the shockwave lab and a visionary investigator of the properties of rocks and minerals as they undergo shock compression. When it was time for Ahrens to retire, there was an understandable desire to keep his lab operational, given its singular capabilities and the obvious promise of future discovery. Asimow agreed to take over the lab - not in a caretaker role but on the basis that he would incorporate this research into his broader work. That decision continues to pay important dividends to this day, thanks in large part to a dedicated professional staff that is dead serious about safety and scientific integrity.

In recent years, Asimow has increasingly turned to field work. The Earth's natural beauty is one of the reasons he got into geology, but between his initial and exclusive focus on computational and laboratory research - and the enhanced feasibility of taking long trips when one's children are not too young - this aspect of Asimow's career has been a long time coming. Either as a consumer or producer of field data, Asimow shares important insight on how the most successful geologists can ensure scientifically fruitful results, and why even the greatest advances in simulation cannot and should not replace the truth that can be gleaned from real-world analysis. Reflecting on his own childhood and his recognition that his appreciation of nature rested on a privileged upbringing, Asimow has become an energetic promoter of diversity and inclusivity in geology, where the benefits both to students and to the science are self-evident.

Beyond science, Asimow has deep musical roots that go back to his ancestors in Eastern Europe, and he is an accomplished and classically trained tuba player and musical arranger. He came to the tuba by way of the piccolo - the largest size differential he could have crossed, from the biggest of the brass to the smallest of the woodwinds. Although he keeps his musical and scientific worlds separate, it is interesting to think of the parallels he has pursued in both musical and scientific range.

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Tuesday, March 21, 2023. I am delighted to be here with Professor Paul D. Asimow. Paul, thank you so much for having me in your office.

PAUL D. ASIMOW: You're welcome.

ZIERLER: To start, would you please tell me your title and affiliation here at Caltech?

ASIMOW: I am the Eleanor and John R. McMillan Professor of Geology and Geochemistry in the Division of Geological and Planetary Sciences at Caltech.

ZIERLER: Tell me about the McMillans. Who are or were they?

ASIMOW: I don't know very much about them. John R. McMillan I believe is an early alumnus of the Caltech Geology program who, like many of the early alumni of the Caltech Geology program, made quite a bit of money in oil in Southern California. He and his wife, Eleanor, gave some of it back to the Institute to endow a chair. That's about what I know about the McMillans. I carry the title, but I haven't dug deeply into their relationship or their history.

ZIERLER: The title—Geology and Geochemistry—does that suggest some kind of dual appointment or does that just encompass your research areas?

ASIMOW: The Institute is organized into divisions and options. An option is a degree-granting program typically within, but not necessarily restricted to, a single division. The GPS Division now has six options: Geology, Geochemistry, Geophysics, Geobiology, Planetary Science, and Environmental Science in Engineering. Having two options in my appointment indicates that I am a full member of two of those options, that I help to design the curriculum and administer the program in two options, that I participate closely in graduate admissions in two options, and that it doesn't really make sense to try and pigeonhole me into one or the other because my research encompasses both and crosses the line.

ZIERLER: What does that mean for your graduate students? Are they divided among those options?

ASIMOW: And others. Within the GPS Division we think of an option as defining your course requirements and, to some extent, which building you'll sit in and who your academic advisor will be, but you can do research with anybody in or beyond the Division. Most of my students are in the Geology option or the Geochemistry option, but I have been thesis advisor to Geophysics students and Planetary Science students and Materials Science students and Chemistry students.

New Directions in Shockwave Research

ZIERLER: That's a Caltech story, really—all over the map. What about the Lindhurst Laboratory? Are you still PI of that?

ASIMOW: I am. The Lindhurst Laboratory was built by Professor Tom Ahrens, who came to the Seismo Lab in 1966 and built a simple shockwave lab at the San Rafael facility where the Seismo Lab used to be. When South Mudd was built in 1974, Caltech received a significant gift from the Lindhurst family to build Tom a bigger and better lab, and that was pretty much the end of our involvement with the Lindhursts. I don't have any continuing relationship with the family. There are a couple of souvenir hardhats in the lab that the Lindhursts wore at the groundbreaking in 1974, but that's about it. I was not involved with shockwave research when I was here as a graduate student, but once I was hired to come back and join the faculty, I got into various discussions with Tom Ahrens who played a very long game seeing his retirement coming and not wanting his lab to disappear. He gradually drew me into the science that they do in the Shock Wave Lab, initially as a co-investigator on a proposal while I was a postdoc and anticipating coming back, and then a co-principal investigator on the next round of proposals, and then principal investigator on the next round of proposals, and by the time Tom retired in 2006, I was running the place.

ZIERLER: What aspects of the lab have you made your own, and what aspects are really a continuation of what Tom built?

ASIMOW: Most of the main physical infrastructure—the big guns that we use to generate high pressure shockwaves—are still essentially what Tom built. I have had to replace the staff. I have had a complete turnover. Running a lab like that is absolutely dependent on long-term retention of dedicated and qualified and experienced technical staff. You just can't do it without staff that stay for a very long time because there's so much lore. There's no training program anywhere that teaches someone to be a technician for a lab like this. They have to learn it on the job. And so, Tom benefitted from having two staff members from the 1970s into the 2000s and I have benefitted from having a little bit of overlap between those technicians and the people that I hired and have been able to retain the people that I hired for 10, 15, 20 years.

ZIERLER: How much is the importance of stability and staffing about safety considerations, given what that lab does?

ASIMOW: It's both safety and productivity and quality of the data. We academics don't think of what we do as a job, and we internalize as a deep personal motivation that we want to do the best science we can do and that we don't want to generate bad data or publish bad data as a matter of personal reputation but also, it's kind of our purpose in life. It's very hard to find staff people who think of their work in that way rather than "This is a job, and I'm going to show up and do what is asked of me and then I'm going to go home." You need people who both value their own safety [laughs] and therefore the safety of those around them, but also participate to some extent in the mission and feel the excitement and understand why they're being asked to do this exactly this way every time, not just so that it's being done safely, but so that the data are reliable and nothing gets broken and the lab can continue operating over the long term. For work like that, when you're looking for staff, you're really looking for people who are going to make it their own and be a partner rather than just an employee.

ZIERLER: Given that the infrastructure of the lab is so similar to what Tom originally built, what are the open, ongoing questions that demand doing similar kinds of experiments all of these decades later?

ASIMOW: The basic infrastructure accelerates projectiles to high speed. What you do when you stop them can evolve and be replaced and be upgraded. So, we have improved our detectors. We have learned to build more complex targets. We have moved towards faster shots and higher pressures. My interests and Tom's are not exactly the same. Tom was a professor of Geophysics and Planetary Science and was a member of the Seismo Lab Group. I'm Professor of Geology and Geochemistry—not a member of the Seismo Lab, which is a little weird because my lab is in the sub-basement of South Mudd and is the laboratory of experimental geophysics, but that's—

ZIERLER: But your collaboration with Mike Gurnis—they do have relevance with the Seismo Lab.

ASIMOW: Right. I came into the shockwave work as an igneous petrologist, as someone interested in the melting and crystallization of rocks, and the evolution of planets by melting and migration of magma from one place to another. Tom came in from a physical perspective of ballistics and cratering and planetary surfaces. And so, we use the same equipment but we have different science questions in mind, to some extent. Tom was also very broad in his interests and had a very successful collaboration with Ed Stolper that showed what could be done in igneous petrology and the understanding of magma at high pressure, starting in the 1980s. That's the main thread that I've picked up and extended and applied to higher pressures and what goes on in the Earth's lower mantle rather than just in the upper mantle.

The world of shockwave research has to a significant extent moved on beyond what can be done with guns. Most people in the field are now using high-powered lasers—national laboratory kind of platforms—to generate much more intense shocks. But they last for a much shorter time, the targets are much smaller. In my view, the quality of shockwave that you can generate with lasers, although it's stronger, it is not as good, not as precise, not as uniform. And so, I have been able to carve out, for now the past 20 years or so, a niche of, "These are the things for which guns are still the right tool and this is work that still needs to be done," even though much of the field has moved into different areas using much more expensive, much more elaborate tools to generate higher pressures.

ZIERLER: There's still things guns do best, at the end of the day? [laughs]

ASIMOW: That's my assertion, and I've so far been able to convince funding agencies of that. [laughs]

The Centrality of Igneous Petrology

ZIERLER: To go back to Geology and Geochemistry in your title—what is your home discipline, or the umbrella discipline under which everything falls? There's geology; there's earth science; there's petrology. By your education or by the recurring themes throughout your career, what would you consider the foundational discipline?

ASIMOW: I'm going to say igneous petrology, which some people might perceive as a specialty niche within geology, but to me it's an umbrella that covers any way of thinking about melting and crystallization processes, which I assert are fundamental to the geological record, but also to the geochemical evolution of, and the origin of, planets, and the geophysical dynamics of planets. So, it's a way into a wide range of problems. Whether I'm doing shockwave experiments, or static high-pressure experiments, or low pressure experiments, or computational thermodynamics, or first principles calculations, or fieldwork, or analytical work on real rocks—all of those are basically aimed at this phenomenon of melting and when it happens and how it happens and why it happens and what happens as a result.

ZIERLER: In the way that igneous modifies petrology, are there other "-blank-" petrologists?

ASIMOW: Of course. So, petrology—a word that confuses a lot of people because the root petros, which just means rock—we most often hear in the context of petroleum, which is oil—oleos—that comes from rocks. Petrology is just the study of rocks, which to many people sounds like geology, but geology is the study of the Earth which has many parts and many ways to approach it even though much of it is made of rocks. So, petrology is just that. Above the level of minerals, which is what rocks are made of, and below the level of terrains, which are complexes of many kinds of rocks at the regional scale, we have the rocks themselves. Classically, we divide rocks into igneous, metamorphic, and sedimentary. We can also divide petrologists into igneous, metamorphic, and sedimentary. Sedimentary petrologists are looking at how sediment, particles that have been eroded and transported and deposited somewhere, are converted into a rock, and what you can learn from their size, distribution, the combination of minerals that you find in one place, how they are cemented together, how they were transformed from sediment into a rock. That's sedimentary petrology. Metamorphic petrology, you're basically trying to establish the pressure–temperature–time history that a mass of rock passed through from its untransformed state to the final state in which you find it, which tells you about how mountain belts are built and then eroded. It tells you about how close you were to hot sources like igneous intrusions. It is based on the fact that if rocks don't get too hot—if they don't get so hot that they melt or that diffusion re-equilibrates them completely—then they have memory, at least some partial imperfect memory of earlier states that they have passed through.

So, metamorphic petrology depends on the existence of disequilibrium, of reactions that did not go to completion, because if everything went to completion, every rock would just tell you about the state that it's in now. Igneous petrology is looking at rocks that were once, at least partially, molten. Equilibrium, and therefore thermodynamics, is a much more useful tool because once things start to melt, they do pretty much approach thermodynamic equilibrium and forget what came before to a much more significant extent. In many of the things that I do, really the intellectual framework—the rigorous scientific principle that I am able to bring to my interpretations—is classical thermodynamics and tools that were developed by the thermodynamicists of the 19th century. I try to bring it into the 20th and 21st century wherever I can, but a lot of the classical knowledge that mostly all came together in the work of Josiah Willard Gibbs is really at the root of my method of understanding what information I can get from a rock and what it can tell me.

ZIERLER: Paul, the idea that rocks have memory and can even forget, what aspects of that are anthropomorphizing for our own shorthand, and where do you literally mean that rocks have memory?

ASIMOW: I mean it perfectly literally. Thermodynamic equilibrium means everything has changed that wants to change and you have reached a state that is entirely determined by the current conditions, and it has forgotten—literally forgotten—any previous conditions because thermodynamic equilibrium is path-independent. Anything about the system that has persisted from previous conditions that were applied to it—that's memory. That is a record that allows us to, in principle, reconstruct the evolution of that system over time. Preservation of evidence of earlier conditions is what I mean by memory. So, sure it's not encoded in neural pathways the way that brains form memory, but I think it's a very plausible and not anthropomorphized analogy to say that there is preserved evidence in a rock, in its minerals, in its chemical composition, in its texture, in its isotope ratios, of earlier states.

Perhaps one of the more literal applications of this is geochronology—how do we tell time? How do I know how old a rock is, and what do I mean by, "How old is a rock?" The rock is made of atoms. The hydrogen and helium are 13.5 billion years old. They come from the big bang. The other elements were synthesized in pre-solar stars that underwent various supernovas and events that eject nuclear matter into space, so it was available to collapse and form our solar system. But for igneous rocks, we usually mean, "When was the last time it melted and crystallized?" For sedimentary rocks we mean, "When was it deposited?" For metamorphic rocks we generally mean, "When did it reach its peak highest temperature and pressure?" Geochronology attempts to tell time on an absolute basis—number of years, not just, "This happened first, and this happened later"—using various kinds of clocks. And to be useful, a clock needs two things. It needs to run at a reliable rate, and someone has to have reset it at some fixed, well-defined time that you are then measuring from. If I give you a stopwatch and it's running, what does it mean? Well, when did somebody stop and reset the watch and start it? Igneous rocks are typically the ones that people date—that people measure the age of using radioactivity—because an igneous event erases the memory of prior events and resets the stopwatch. It equalizes isotope ratios throughout the rock. It drives off all of the argon, or all of the helium, because they're gases and easily escape at a high temperature, and then once you cool it, they start accumulating and you get something you can measure. If your clock is remembering, even in a blurry way, times before time zero, it's very hard to measure, "When was time zero, and what do I mean by time zero?"

ZIERLER: Either directly or indirectly then, how has your research contributed to studies about the age of the earth—geochronology?

ASIMOW: It's not my field, directly. I have been tangentially involved with Ken Farley's development of methodology for thermochronology, which is a field of geochronology that operates at fairly low temperature. Instead of trying to say, "When did this rock melt?" it asks, "When was this rock buried deeply enough that it was above some critical temperature?" And therefore, "How quickly has erosion been unroofing it and bringing it to the surface?" Ken's method depends on the retention and loss of helium—which is an alpha particle, so it's the decay product of uranium and thorium—originally in the mineral apatite—which is calcium phosphate—that concentrates uranium.

In order to have a useful chronometer from the accumulation of helium, you have to know the details of how helium diffuses out of apatite, which requires controlled experiments at very precisely known temperature. One of the pieces of equipment that I inherited from my predecessors—in this case, from Peter Wyllie—is a series of furnaces with pressure vessels where we can generate high pressure—in this case on the order of hundreds to thousands of bars—and have a thermocouple, which measures temperature to the nearest degree or so, close enough to the sample that we really know the temperature of the sample. The calibration of that method, originally by Richmond Wolf and Ken Farley, was done in my lab. Likewise, not about the age of the Earth, but my colleague John Eiler, who someday is going to win all the big prizes in geochemistry for his very bold development of clumped isotope geochemistry—which is looking not just at the total number of odd isotopes in the system, but how often they are together in the same molecule or same molecular group—that method also requires very well-known temperature-controlled experiments, and that was also done in my lab. I also worked a little bit again with Ken on an instrument to measure ages of rocks that could be flown to Mars and put on a rover and do geochronology—I'm not sure geochronology is exactly the right word; areo-chronology perhaps—in situ on Mars. That instrument did not end up being selected for the Mars 2020 rover, but it was an interesting development exercise.

ZIERLER: Bringing rocks to Mars?

ASIMOW: Actually, in a way, yes. The method requires being able to pick up a rock on Mars and measure the amount of potassium in it and the amount of argon in it without weighing it and without actually measuring a potassium-to-argon ratio, which is hard to do accurately. And so, it requires mixing the sample with what we call a spike, an artificial material that has exotic potassium and argon isotope ratios that we prepare and preload into the spacecraft and send to Mars.

ZIERLER: This is all how to keep things interesting before a Mars sample return.

ASIMOW: Yes, exactly. I've been involved with various kinds of helping out my geochemical colleagues who are working on developing new geochronometers. I've also collaborated on dating a variety of rocks for a variety of reasons, but mostly my shockwave work, because it's been aimed at understanding the properties of magma at very high pressures—where magma typically does not occur anymore because the Earth is too cold—informs the way that people have thought about the very early evolution of the Earth, and in particular, the evolution of what we call magma oceans. A magma ocean, classically, is what happens during the period of heavy bombardment when there are constant large impacts that melt surface regions of a planet. If you keep up the impact flux enough, you keep remelting it before it freezes, and you end up with a planet covered with some thickness of melt.

The largest impact that we think we know about is the one between the proto-Earth and a Mars-sized object that is likely to have created the Moon somewhere around 4.52 billion years ago, which, in most models, leaves the Earth in a completely molten state—mantle molten all the way to the bottom. It's not in that state anymore, so you've got to freeze it, and that sets the initial conditions for everything that comes after. So, understanding what a 3,000-kilometer thick layer of magma of average mantle composition would do and how it would freeze and what record there might be still readable on the Earth today of such an event. That's the grand challenge of why [laughs] I've been going to all of this effort to measure the density of magma at conditions where there isn't any magma anymore. So, it's not directly related to measuring the age. We think we know the age of these events based on what we've been able to do principally with Moon rocks which are all very old and remember this era. There's not very much rock record on the Earth that dates back to this time. For obvious reasons, you melted everything. [laughs]

Forays in Planetary Science

ZIERLER: As you've alluded, there's aspects of your research that are purely terrestrial and aspects that are focused on other planets, or other celestial bodies. What are the areas that you see as purely celestial, purely terrestrial, and perhaps most interestingly, where are the connecting points that enrich both aspects?

ASIMOW: I'm primarily interested in other planets not from an exploration point of view but from a comparative planetology point of view—alternate scenarios, alternate experiments that went down a different pathway from the pathway the Earth went down, and why. What are the branch-points that make, say, Venus Venus-like and Earth Earth-like and Mars Mars-like? The fascinating details of the current state and the history that we can read of the environments on other planets—I'm always trying to get back to the root of it. Why did it get to be that way? I am also, unlike many people that study Mars, not especially motivated by trying to find evidence of life on Mars. I have always thought that NASA is making a mistake by focusing so much of the motivation for the Mars research program on the search for life because if you never find it, what was the point? And that's a very strong possibility.

Over the arc of my career, I actually started out in planetary science as an undergraduate. We'll get into this I suppose in the next interview, but I discovered planetary science as an undergraduate at Harvard. I wrote a senior thesis about impact processes on Venus. I was admitted to Caltech by the Geochemistry and Planetary Science options because I said I was interested in meteorites and I was looking for a school that did both Earth science and planetary science in the same department or division so that I didn't really have to commit to one or the other yet. And then, I had a really negative experience with mission bureaucracy and politics and whether I could keep working on Venus, after I graduated from Harvard and no longer was a student of a member of the Magellan Science Team. I was offered a very interesting problem—I mean essentially terrestrial petrology here—and so I said, "I'm done with planetary science. I'm going to generate my own data in my own lab or in my own computer and not depend on missions." I pretty much kept that up for about 20 years.

ZIERLER: [laughs]

ASIMOW: But there is so much interesting work to do, and you can learn so much about the Earth and about terrestrial planets in general from looking at more than one, that I've allowed myself to be drawn into more planetary problems here and there.

ZIERLER: As you noted, I'm curious the extent to which JPL has been an asset for your research over the years, and if it has pulled you into research projects that you weren't expecting.

ASIMOW: Yes—not a key asset for the most part. I've only been distantly involved with JPL and with missions. I do have a PhD student right now who is working on Perseverance data, but even so it's not by any means the main area that I'm working in. I don't have the time and the dedication to follow mission operations at the level of detail that the constant stream of data and decision making that actually involves operating a mission requires. So, yes, I have had several collaborations with JPL, but I don't feel like they've really been central to my career at this point.

ZIERLER: Running laboratories, working as an experimentalist, do you serve as your own theorist? Are there theories that you rely on that provide an intellectual framework for what the data is telling you?

ASIMOW: Yes. I am by no means a pure experimentalist. I like having in my own mind the ability to approach problems from multiple perspectives. When necessary, when I go beyond my own expertise, I will collaborate with theorists, but for the most part, I am, indeed, my own theorist.

ZIERLER: What's an example of collaboration where you need expertise beyond your own?

ASIMOW: When I first realized that I needed to get beyond the classical thermodynamic level to the atomic level to understand what was going on in silicate liquids. I realized I was going to have to start doing ab initio simulations or empirical molecular dynamic simulations, and I wasn't going to learn that from scratch or be able to really train a graduate student without a co-advisor. And so, I have worked closely with Bill Goddard from the Chemistry Division over many years now on training my students to do, and then gradually training myself to understand and use intelligently, molecular simulation methods applied to natural materials, especially minerals and magmas. Goddard has been my closest collaborator outside the GPS Division for quite a few years now.

ZIERLER: The phrasing is interesting, "Beyond thermodynamics to the atomic level". Is that to say Newtonian physics doesn't have much to tell us about matter at the atomic scale?

ASIMOW: Molecular dynamics is a semi-classical approach, or sometimes an entirely classical approach. It basically says, "We can treat the electrons as quantum particles and the nuclei as classical particles," and that's the Born-Oppenheimer approximation of separating those two time scales and mass scales. Because if we know where all the nuclei are—they are basically point charges and they exert forces on each other, just regular electromagnetism. If we know where all the electrons are in a probabilistic sense—if we know the wave function—then we know the forces between the electrons and the nuclei and now we know all the forces on the nuclei and now we can just apply Newtonian mechanics to say, "This is how the nuclei are accelerated by those forces." And we take a small time step, move the atoms, update their positions and velocities. And then, if we were to stop for a moment and say, "Now the atoms are here. How does the electron distribution respond?" now again we know all the forces. Now we can use Newtonian mechanics to accelerate the nuclei again. So, it's a semi-classical method in that the electrons are treated using density functional theory, which is an approximate implementation of quantum mechanics—it's a recasting of the Schrödinger equation—but the nuclei are just basically ballistic masses with charge obeying Newtonian mechanics according to the forces on them. That's molecular dynamics. It is computationally expensive to solve a many-electron density functional theory problem every femtosecond for systems with many electrons.

ZIERLER: Expensive because that's a storage issue? Just a huge amount of data?

ASIMOW: No, it's computationally expensive. It's a lot of CPU time. Essentially because the basis functions that we use to decompose the wave function require many, many, many terms in the sums to approximate accurately enough what the electron density is so that we can then get accurate enough forces so we can then move the atoms correctly. No, it's not primarily a storage problem; it's primarily just CPU time. It's very parallelizable. It works nicely on clusters.

ZIERLER: This is to say parallel computing has been very important for you?

ASIMOW: Absolutely. For problems that are too hard for the state of the art in computing directly the first principles molecular dynamics, we turn to empirical molecular dynamics, meaning we make up some function that describes what the forces on the atoms are, and that function is very quick to evaluate, and so, now you can run simulations of millions of atoms for long periods of time. By long, I mean milliseconds—

ZIERLER: [laughs]

ASIMOW: —instead of what the state of the art in ab initio molecular dynamics is—hundreds of atoms for hundreds of picoseconds. When you get to large-scale problems that you cannot address with hundreds of atoms or that require long time scales that you cannot address with hundreds of picoseconds, you have to turn to empirical molecular dynamics, which is only as good as the force field. So, a lot of Bill Goddard's work has been developing better force fields to do better empirical molecular dynamics on fairly large-scale systems that you need to understand the kind of problems he's interested in, like catalysis.

A magma is a system that is hard to address with a few atoms on a short time scale because it's not periodic. In a solid, you can just solve the dynamics of one unit cell and now you understand the whole solid. Liquids don't have unit cells. We're often interested in complex compositions that need many atoms, and the effect of a small concentration of some element may have an outsize influence. If you don't have a lot of atoms, you can't have a small concentration of one atom because you need a big denominator to get a small concentration. And liquids have long time-scale behaviors, especially at low temperature. They have memory, if you will, in their configuration of the series of pressures, temperatures, volumes, that they have passed through, and it takes—depending on the temperature—maybe a long time for them to evolve. A classical example of this is the glass transition. A glass is a super-cooled liquid whose time-scales of memory are longer than the time-scales over which you're changing their temperature, and so the classical glass transition is observed when the relaxation time gets to be larger than about a second. We can heat things up and cool them down at a Kelvin per second and if it stops keeping up with changes in temperature, it's a glass. So, if I want to be able to understand a glass, I have to be able to run a simulation for a whole second and I can't do that ab initio. The classical ways of doing that involve using human judgement to decompose the forces among atoms into various terms and then attempt to find functions that parameterize those terms and then calibrate the coefficients of those functions. The new way to do it is like the new way to do many things, which is, take away the human intelligence and use machine learning and just throw a vast amount of calibration data—either experimental data or ab initio calculations—into the input port of a neural network and let it decide what the function is that will then output the forces. There's a number of research groups that have been going in that direction. I'm thinking of going in that direction in the near future.

ZIERLER: You've been convinced of the value of machine learning?

ASIMOW: No.

ZIERLER: You're willing to try, though.

ASIMOW: I'm willing to try. [laughs] Yes, that's well put.

Connections to Applied Research

ZIERLER: Paul, a question about fundamental research versus potential application. Obviously almost everything that you do would be considered basic science, curiosity driven. Are you ever motivated by particular applications, or have you seen your research become of interest in industrial settings, and have you gotten involved if it has?

ASIMOW: A little bit. The apparatus that I have is dual use. You can study natural materials. You can study synthetic materials. You can synthesize imitations of natural materials. You can synthesize new things. So, I advised some years ago now, a materials science student who had a falling out with his advisor in materials science but was already working in my lab because they needed high pressure. And so, I was the advisor to a PhD thesis about thermoelectric materials. Thermoelectrics are materials that generate a voltage when subjected to a temperature gradient, or conversely, will transport heat when an electrical potential gradient is applied to them. So you can use them as active cooling agents; that's the Peltier effect. You can also use them for power co-generation. Any place you have waste heat, you may as well coat the boundary between the hot part and the cold part with thermoelectric materials and generate power. Of course radioisotope thermoelectric generators which power spacecraft are using thermoelectric materials to convert the heat from the plutonium into usable power. You want them to be good thermal insulators so that you don't just lose your heat by conduction. You want them to be good electrical conductors so that you don't waste all the voltage you've generated just getting through the thermoelectrical material itself. These properties define a standard for what makes a good thermoelectric material. And so I got involved in synthesizing some interesting candidates that required high pressure to get into their stability field. That ultimately did not lead to any patents or any commercialization. Much later, maybe five, six years ago, I was approached by a group from USC that is interested in sodium ion batteries as a green alternative to lithium ion batteries, and they had a theory that synthesizing their anodes at high pressure would make them more stable in higher performance. I said, "Cool. Let's collaborate." We made some graphene phosphorus composites at high pressure in my experimental apparatus that turned out to perform very well, and there is a patent on which I am a co-inventor for layered graphene high pressure phosphorous anodes for sodium ion batteries. Nobody's commercialized it yet, but it's out there. I have been involved for several years now in the story that may have come across your history desk at a few points which is quasicrystals.

ZIERLER: Yeah! Sure.

ASIMOW: We've learned to make quasicrystals by shock synthesis in my lab, originally to test whether the ones that are found in the Khatyrka meteorite that Paul Steinhardt found are—are they really natural? And why are they there? And the answer to why they are there is you can easily make them, if you have the right starting materials, with shockwaves. And now we've learned that not just the kinds of shockwaves that result from asteroids running into each other, but also shockwaves generated by nuclear explosions, shockwaves generated in my laboratory, shockwaves generated by lightning strikes or electrical discharges—all of these things will make quasicrystals.

In principle, quasicrystals may have industrial applications because they have a range of exotic properties. They have not been extensively commercialized. The only application that's reached the market is nonstick coatings for cookware as an alternative to ceramics and that performs to a much higher temperature than Teflon. I do have a visitor who is here now who is interested in potential commercial applications of quasicrystals and materials. He's interested in their magnetic properties and is making quasicrystals with rare Earth elements in them that could potentially be more powerful magnets than classical crystal and rare Earth element magnets, or that could exploit a number of quantum level effects to have very interesting electronic or magnetic properties. So, we are actually collaborating with the Rosenbaum Lab to study some of these quasicrystals that we have synthesized by shock at cryogenic conditions to see if they are superconductors, if they are spin glasses, if they exhibit magneto-resistance or magneto-caloric effects or a variety of complex and interesting physical properties of ordered and disordered magnetic spins that I don't actually understand in detail, but I'm willing to help on the experimental end and try to keep up with the theory.

The Pull of Fieldwork

ZIERLER: Paul, tell me about fieldwork for you. What are the kinds of things that compel you to go out in the field?

ASIMOW: I should acknowledge that the notion of fieldwork—of being able to travel and spend time outdoors and be paid for it as an inherent part of my work—is one of the things that drew me to Earth science in the first place.

ZIERLER: You love the outdoors.

ASIMOW: Absolutely. And we'll get into this, but one of the beautiful things and one of the challenges about Earth science and in particular about diversity in Earth science is, who has the opportunity to get an appreciation for the outdoors, to learn to love the outdoors, to learn to feel safe in the outdoors, and therefore understands this motivation to study the Earth. There are social and ethnic and racial and gender biases in the availability of that experience to people for sure, and it's one of the things that makes Earth science lag behind other fields. But I absolutely had a father who was interested in the outdoors and took us camping and gave us that appreciation, and so I always had that. Fieldwork is challenging and knowing when there are problems that can best be addressed by fieldwork is challenging, so that you're not just tramping over the same ground that has been tramped over before. It's not necessarily my greatest gift. I have not had that many opportunities to do field research, but when such opportunities arise, I take them, and then I remember that this is why I got into this field in the first place.

ZIERLER: Yes! [laughs]

ASIMOW: Remembering back, I was admitted to graduate school here in Geochemistry and Planetary Science, but my degree is in Geology because the difference between being a Geochemistry PhD student here and a Geology PhD student is that Geology students all have to take three quarters of advanced fieldwork, and I wanted to do that. So, I said, "I'm going to be a geologist and do the field work training. Whatever my research ends up being, whether any of it is field based or not, I want to have those skills. I want to get out of doors with these really great field instructors and learn how they look at the world." And at some point we'll get into the great field instructors that I had the opportunity to work with.

After graduate school and being trained in fieldwork, there were long periods of time when I didn't get to the field much at all. After I finished here, I did a postdoc at Lamont-Doherty Earth Observatory, which is a kind of an oceanographic institution and sends people to sea a lot. I didn't actually go to sea while I was a postdoc, but I learned to work with data from rocks collected from the sea floor. A few years later, my postdoc advisor, Charlie Langmuir, invited me on a research cruise. I was able to spend 35 days at sea in the South Pacific collecting rocks—back when I was an associate professor—and that was a very interesting experience. I haven't gone back, but I liked doing it once. The last seven years or so, I've been much more involved in research on real rocks collected from the field, mostly by other people in areas that I may not have gone to, but they come to me to collaborate because I have resources to analyze and interpret their rocks. But I was able to put together an expedition in 2018 to Baffin Island in Arctic Canada to collect samples and bring them back and interpret them. This past summer, I went to Cameroon in West Africa because we hired a postdoc that I had been working with in this mode of, "You do the fieldwork there in Africa and send me the rocks; I will use all these expensive analytical machines that we have here to generate data and send it back to you." But after he finished his PhD, we hired him as a postdoc here and his project involved fieldwork there in Cameroon, so I said, "I'm coming. [laughs] I want to see the field area. I want to get my boots dirty." And that was pretty exciting.

Apart from those trips—the research cruise near Tonga, the expedition to Baffin Island, the expedition to Cameroon—apart from that, my fieldwork has been teaching. I run field trips for students mostly for inspiration rather than for research. In other words, as part of being educated as a geologist, you really ought to get out and see the world. And so I haven't taught any of the kind of specialty courses that involve really digging into a particular field area and milking it for information. I've taught the introductory-level courses where the fieldwork is more about getting out there, getting back [laughs], gaining an appreciation for how you look and see what's in the field, and getting the spark of excitement to want to go out there and do it again for longer and more detail.

The Value of Laboratory Simulation

ZIERLER: This is probably as much a philosophy as it is a science question. Back in the lab, when you do simulations, what is the utility of simulations in terms of the real world, and where are its obvious end points? Where is the natural point that which you say, "It's not real life. We can only infer so much as a result of simulation"?

ASIMOW: The Earth is arbitrarily complicated. It has information and effects at all spatial and temporal scales. We accept when we go to some region, or when we look at a planet, that we are not going to solve all problems completely and understand everything from the atomic to the planetary scale, and from the femtosecond to the billion-year time-scale. Nobody can do that. It's too much information. So, everybody ignores some part of the problem and grapples with the part of the problem that they can wrap their heads around and make some progress on.

A simulation, even if it's a multi-scale simulation, addresses some part of this complex problem and hopefully gives you some insight into that aspect of the problem, which allows you to push up against the boundaries of, "If I have this very nice coherent theory that explains this one thing at this one scale about this system, where do I lose resolution? Where do I get out of the domain that my simulation is applicable to?" Those are hard questions, and it's the reason that qualified, educated, intelligent, well-meaning people can sharply disagree [laughs] for years on end about aspects of Earth science because they're each coming at it from their own perspective, and they're each right from their own perspective, but neither of them is completely right. What I have found to be a really useful approach—and I learned this from Ed Stolper—is to find the simplest model system that has the essential behaviors you are trying to describe, in which you can understand the origin of those behaviors in complete detail. No simpler than that because then you don't get any insight, and no more complex than that because you cannot build intuition. If you can't test all of the characteristics of your model system, describe and choose the aspects of that model system that you think can be extrapolated to more complex systems and work up from there to the level of complexity where you can no longer make progress.

The kind of work that I started doing in graduate school and that drew early attention to me and my work—I have been a long-time user of a model for understanding igneous petrology using classical thermodynamics that is applicable to fairly complex systems with many chemical components—six, seven, eight, ten chemical components. Meaning, to represent them completely, you have to be able to see in about 12 dimensions—10 chemical dimensions plus pressure and temperature or something like that—and you can't do it. But this is the level of complexity that is present in real rocks because only a very few specially chosen rocks on the Earth are chemically pure enough to really be understood without involving many elements. Using that thermodynamic model, I discovered an unexpected behavior that was quite contrary to the accepted wisdom about how these kinds of rocks melt. And Ed's first response was, "That's wrong. Go do it again."

ZIERLER: [laughs]

ASIMOW: I did it again. I convinced myself that the model was right, but neither of us could fully understand why the model was doing that because the model was complicated. And so, we simplified it. We found a model system that we could draw on a Starbucks napkin, over there at Lake and California, and we worked that up into a complete description of a simple system where nobody could argue with our interpretation because it was complete and rigorous and robust and there was no wiggle room in the one-component system, chemically pure, just the only variables are pressure and temperature or entropy and pressure is actually the right way to look at it. We found this behavior in the one-component system, and then we demonstrated it in the two-component system, and then we extrapolated back to the complicated thermodynamic model system where we saw the behavior in the first place and convinced ourselves that it was right because it had the behavior we saw in the very simple system that we could understand fully. Basically, our argument was, "This is the right model system to work up to the complex system."

That's still only a model. It's a model of a process that you cannot simulate experimentally, and you cannot observe directly because it's happening slowly and at great depth in the Earth, but it gives us a framework for now interpreting what we find in natural rocks that actually erupt at the surface of the Earth where we can pick them up and say, "How was this generated? At what depth? At what temperature? By what process?" If you hadn't gone through that whole thermodynamic exercise, you would allow a possibility—a theory—that is in fact rejected. It is excluded. It is disproven by the theory. There's of course still a range of processes that have not been disproven—that's how science works—but the short answer, I guess, to your original question is: models allow you to disprove things that are impossible and limit the imagination space of things that remain possible.

ZIERLER: Paul, some questions on technology. To stay on the simulation side, what have been some of the computational advances that have really revolutionized your capacity at modeling?

ASIMOW: Like anything else, the growth and the availability of storage and computational cycles. When I started using this model, it had just been translated from Fortran to C, and it took hours to compile on the workstations that were available in the mid-1990's. Anytime I wanted to make any change to the code, I then had to twiddle my thumbs while it compiled before I could run it.

ZIERLER: [laughs]

ASIMOW: We could run calculations at a rate that— the model that I developed that kind of does a full description of what we think happens under a mid-ocean ridge took about 20 minutes to run. Now, due to having more memory in the computers, basically the compilation takes seconds and so it's much easier to update and improve and debug the code. That's an order of magnitude or two more efficient, and that model now runs in 20 seconds instead of 20 minutes. And so, you can explore a much wider parameter space in a reasonable amount of time. In terms of the classical thermodynamic modeling of magmatic systems, it's more efficient to write and improve the software, and it's more efficient to run it. It has been so transformative that we could do things now that we really couldn't do then, at that level. The other thing you often want to do with these models is embed them within other models. The model says, "Okay, if this is the chemical composition and the pressure and the temperature, what is the thermodynamic state? Which phases are present? Is it molten? If it's molten, how much melt is present, and what's the composition of the liquid?" If I know that, I know the density. I know the viscosity. If the liquid is going to separate, I know how fast it can move. It's all very useful information for embedding in a fluid dynamic model of how things move around at regional to global scale in the Earth. This is what geodynamicists do. This is what Mike Gurnis does.

So, Mike Gurnis can tell me how the heat and the mass is moving around the system, but if I can tell him as a result of that—Is it molten? And what's the density? And what's the viscosity?—then he can tell me much better what's going to happen at the next timestep, and which way things are going to move. So, it's a natural thing to do to take this thermodynamic model and embed it in a geodynamic model, but then it has to be fast, and it has to be absolutely reliable. It must give an answer every time you ask it for one. And the couple of times that we have really tried to do this, this is where we've run into trouble—when you are running a model yourself, a few hundred or a few thousand calculations, if some of them fail, it's no big deal. You find a workaround. You restart it. If you want the computer to run millions of calculations, that's not acceptable. So, trying to make the model robust and coming up with fallbacks and workarounds is actually the most difficult part of that kind of application. Parallel computing and originally the construction of the GPS Division parallel machine enabled us to handle problems of moderate scale and do those kinds of applications. It also allowed me to start doing ab initio calculations on tens or hundreds of atoms and make that practical and affordable. Then, with the migration of all of the campus high performance computing resources into the central campus HPC cluster, I've gotten kind of one step further away from the system operators and being able to go and grab them by the collar and shake them and get them to do what I want. Which is the best way to get system operators to do what you need. Sending them e-mails is much less efficient.

ZIERLER: [laughs]

ASIMOW: [laughs] But the efficiency of what resources you can run on a laptop that you can carry with you, that you can use for teaching and demonstrations even if you're not on the internet, that has been a significant development over the past 20 years. And the high-performance computing has been a significant development, for sure, for the code integration methods as well as the ab initio stuff.

ZIERLER: We've talked about thermodynamics. We've talked about your work at the atomic scale. What about the quantum world? Your work in quantum modeling, what does that look like?

ASIMOW: Apart from this cryogenic stuff with the quasicrystals now, we were trying to get down to Kelvin and millikelvin temperatures to see whether there are exotic effects going on in those. Apart from that, the only level of contact I've had with quantum mechanics is via density functional theory which kind of smooths over, paints over, the quantum mechanics enough that you can actually practically solve the behavior of multi-electron systems. So, I haven't had to deal with the true spookiness, if you will, of the uncertainty principle and the challenging parts of quantum mechanics. Density functional theory is a way to make quantum mechanics practical and solve real chemical problems at scales larger than physicists typically want to deal with because you've lost already—at that scale of hundreds of electrons, you've already lost the real kind of quantum information science aspects of it. My interests lie at larger scales, so I've only gone down in scale as far as I have to, to be able to predict the behavior that I'm going to see at the scale of a crystal or a parcel of magma.

ZIERLER: NMR spectroscopy, it's a very mature technology, has it improved? Have you used it at various iterations in your career?

ASIMOW: A little bit, yeah. It is one way to solve a couple of useful problems for me in Earth science. One is quantification, absolute quantification, of what are otherwise relative techniques for measuring the concentration of hydrogen in materials. George Rossman has dedicated much of his career to trying to quantify how much hydrogen is present in various minerals and proton NMR is one way to calibrate the otherwise relative techniques like secondary ion mass spectrometry or Fourier transform infrared spectroscopy or Raman spectroscopy that allow us to see hydrogen and allow us to measure differences in the amount of hydrogen between different materials. But there has to be some absolute calibration; that gets back to NMR. The other is the structure of liquids can be addressed to some extent through the structure of glass, obtained by quenching that liquid. Glasses can be studied by NMR, and many of the elements that we are interested in natural glasses have NMR active isotopes. So, you can study what oxygen is doing using oxygen 17, and what aluminum is doing, obviously with aluminum 27, and silicon with silicon 29, and sodium with sodium 23. I have collaborated on a few papers with people that do multi-nuclear NMR of glasses.

One of our alumni going way back, Jonathan Stebbins, who spent his career at Stanford, has really developed a lot of these techniques for using solid state NMR to understand glass structure. His student, Sung Keun Lee, who is a professor at Seoul National University, and I have collaborated on a few papers where we have synthesized glasses by quenching liquids at high pressure in order to try to lock in the structural characteristics of dense liquids at high pressure but then recover them—get them out in the glass state where they have memory—and use NMR to interrogate their structures to see how it's different from glasses that you make at ambient pressure. It's hard. I mean, you have to quench them really fast, or they revert to a significant extent to their original structures. We can do that with static high pressure as long as we can cool it fast enough, and we've tried doing it with dynamic high pressure—that is to say, with shocks—where it seems like it should work better, because you can raise and lower the pressure really quickly with shockwave experiments. That's what they do. The challenge is lowering the temperature enough to avoid back-transformation, and that's very hard. So, we have met with limited success in using shock experiments to recover glasses that have any useful information that you can get out by NMR. That's more been an application of our static high pressure apparatus where we can, counterintuitively I would say, achieve sufficiently fast cooling rates to lock in high pressure information.

Software for Thermodynamic Problems

ZIERLER: Tell me about the development of alphaMELTS software, what that has enabled you to do.

ASIMOW: There's a long parentage there. The intellectual framework goes back to the vision of a professor at Berkeley named Ian Carmichael, who decided in the early 1980s or late 1970s to try to make it practical to apply classical thermodynamics to predicting how igneous systems are going to behave. He realized that to do this you would need several kinds of data. You would need data on heat capacity of the components of silicate liquids. You would need data on the densities of various components of silicate liquids. You would need data on the compressibility which you can get at through sound speed. And you would need a model to take all this data and integrate it into a scheme where you could make predictions of the thermodynamic properties. Ian had a run of amazing graduate students who took on each of these jobs and within a couple of years were doing them better than anyone else in the world. The one that took on the theory problem of, "How do you formulate a model that is simple enough to calibrate in a meaningful way, given the internal consistency and the quantity and the precision of available data, but is complex enough to represent the real behaviors?"—the student that took that on is named Mark Ghiorso. He developed the model through several generations working with a mineralogist named Richard Sack to help him understand the solids, because he was bringing in really new insight about the liquid. When you're looking at melting, you need to understand the liquids and the solids. Ghiorso and Sack eventually put the model that Ghiorso and Carmichael developed into a software package called MELTS, which was published in 1995.

Here, in about 1995, we were doing a reading seminar in igneous petrology led by Ed Stolper and a number of students and postdocs, and we looked at a generation of papers that came out in the late eighties and early nineties that tried to deal with the fact that natural basaltic lavas that erupt at the surface are not actually created by melting at a single point, at a single pressure, at a single temperature in the interior of the Earth. They are mixtures, we were then realizing, of melts that were generated over a range of pressures, over a range of temperatures, separated from their solid residues and then mixed. That process cannot be completely addressed with experiments. One experiment would never, in this framework, correctly predict the composition of an erupted rock because it's just one of the events that goes into the final product. If you can understand that, you're going to need some extended model that takes the results of various experiments and allows you to assemble them into a sequence that could, in principle, generate a realistic volcanic rock. And most of the papers that were doing this were taking a purely empirical approach. They were parameterizing data sets from experiments to get functions that could then be used to predict natural volcanic rocks.

Ed Stolper in his wisdom, said, "These are all junk. This is a thermodynamic problem. This is a problem that we can address using the principles of thermodynamic equilibrium, to govern the functional forms and try to take out the aspect of arbitrary judgment that goes into anybody who says, ‘I'm going to fit these experiments to this particular functional form that has no real physics to it.'" We said, "Who has got a thermodynamic model that could potentially address this problem?" The only one out there was Mark Ghiorso. So, we said, "Let's hire one of Ghiorso's students as a postdoc to come to Caltech and do this problem and spend a couple years and write the paper that says, "What can you learn about basaltic volcanism at mid-ocean ridges using the MELTS software?" So, that was Marc Hirschmann, who was a student of Ghiorso, and came here as a postdoc while I was a graduate student, and brought the code with him, which was not open source code. But I got a hold of it and started learning it and started fixing it and finding bugs and started modifying it to do the things that I wanted to do. By the time we got permission from Ghiorso, I had already found enough bugs that I had demonstrated my usefulness [laughs], and so he accepted this transfer of intellectual property, if you will, through his student Marc Hirschmann to Caltech because we were contributing to the enterprise.

Marc had a number of remarkable visions, including that if you wanted people to use your model, you had to make it user-friendly enough that they could do it even if they weren't programmers because igneous petrologists are very rarely programmers. So, he wrote a graphical user interface so that people could use his model, but the graphical user interface was somewhat inflexible. It could only do the things that Marc anticipated that you might want to do, and I wanted to do other things and I had the code. So, I wrote a very dumb—I don't like graphical user interfaces and I don't feel the need to spend the time to develop them—I just wrote a very dumb terminal text-based menu for interacting with the code that I could quickly adapt to make it do the mid-ocean ridge problem the way I thought it should be done. And in particular, what eventually led to this discovery of this curious anomaly where it was freezing when everybody else said it should be melting, that I talked about earlier with then reducing that to the behavior in the chemically pure system.

So, I then had my own version of the software that had no pretty user interface. The code was a complete mess because I was just writing it for my own use, but it had all of these functions that I was publishing results from. Like Mark, I understood that if I wanted people to not just read my papers but take these methods and apply them to their own problems, I would have to release this software and develop it to the point where other people could use it. And so alphaMELTS is the current name for what grew out of these codes that I wrote for my own use back in graduate school and started trying to release to the world, in more or less user-friendly form in the early 2000s, about when I came back here as a professor. For much of that time, Paula Antoshechkina, who came as a postdoc, proved her value, and I never let her leave—is now a member of the professional staff which is the highest level of the research staff scientist that you can achieve, is a much better programmer than I am, and is dedicated to user support and code maintenance, and has built a large user base of people that understand why they would want to use MELTS, why they would want to get at MELTS through alphaMELTS and why, if they think of something that they want to do with it that you cannot easily do with Mark's tools, if they ask us, we'll make it happen. So, that's pretty much the story of alphaMELTS. It started out—

ZIERLER: It's a saga. That's not a story. [laughs]

ASIMOW: Yeah, I got this backdoor to the code.

ZIERLER: Yeah.

ASIMOW: I made it do things that you couldn't do with the public version and then I tried to make those versions public. And again, having been able to hire and obtain long-term funding through NSF to keep Paula here and keep her working on this project has allowed the project to grow and acquire a user base and for us to run workshops to train people in how to use it. This is the easy way to get highly cited papers, to publish tools that people can use to solve their problems, make them accessible, support them, and the citations come rolling in. I should say that, when you ask Marc Hirschmann did he succeed in the task that he was assigned as a postdoc, which was, "Here's two years. Write a paper that says everything that there is to say about this problem," he says, "I failed." Because it required a dozen papers over 10 or 15 years to really finish that exercise.

ZIERLER: It's a successful career, though.

ASIMOW: Yeah.

ZIERLER: Paul, the duality in your laboratory work, shockwave techniques and static techniques, is this two different methods that are getting at the same questions or are these really separate fields of research?

ASIMOW: Both. There are some aspects of shockwave research that are particular to shockwaves. There are others that are a way to get material to high pressure and measure its properties that is complimentary to what we do with static high pressure. I guess the simplest way to put it is, when we do static high pressure, the variables that we can control are pressure and temperature. We cannot measure entropy. We cannot measure energy. If we want to measure density at high pressure by static methods, we either need a large enough system to get physical separation in a gravity field, or we need to do diffraction which measures spaces between atoms and therefore can be converted to density. If we need to know the pressure in the range where we have gas pressure as our working medium, that can be measured absolutely using things that are directly traceable to force per unit area, but beyond the range where you can safely contain gases, you have to calibrate your pressure. You have to have some way to know what the pressure is.

On the dynamic side, we understand shockwaves and the way that as they travel, they conserve mass, momentum, and energy well enough that we can measure pressure as an absolute number from conservation of momentum without calibration up to very high pressure. We can measure density of a shock material from conservation of mass, even if it's amorphous, even if it's a liquid or a glass and doesn't diffract x-rays and doesn't have time or space to physically separate in a gravity field. We can measure energy because the shockwave is an adiabatic change of state that does work. It imparts kinetic energy but there's no heat flow and that gives us enough constraints to understand energy. We cannot control the temperature, but we can measure the temperature. We can get at these absolute physical variables that we care about in materials—pressure, density, temperature, energy—and reach more extreme conditions without recourse to calibration than we can do in static high-pressure science. But we only get a microsecond or so at high pressure. For laser shocks you only get a few nanoseconds at high pressure. And so only some processes will keep up with the change of state we are trying to impose and yield information that informs us about the long-term information that is equilibrated and is not kinetic.

The problem, for example, of melting a mantle rock—which has four minerals in it, usually—and once you add liquid, you're looking at a fifth phase and you want all of the components to equilibrate amongst all of those materials—that's a static high-pressure problem. There isn't time in the shockwave experiment for all of those materials to communicate with each other and reach equilibrium. So, I can get at the physical properties of each of those minerals separately. Which might be very useful for then saying, "Okay, if I do the static experiments, and I melt this rock and I know that it's 20% molten at this pressure and temperature, if the shockwave experiments have told me the densities of those phases, now I can say physically what's going to happen. The melt is going to go up or the melt is going to go down." I can't solve that problem completely from either approach. I can't get the physical properties of the phases necessarily from the static high pressure, and I can't get the complicated multiphase, multicomponent interactions from the shockwave experiments. So, this is the way in which they are complementary. Then there are things like cratering. I want to know, "Here's a hole in the ground. How big a projectile made it and how fast was it moving?" Static high-pressure science is not terribly useful for that problem. That's a shock problem.

ZIERLER: [laughs] Paul, last question for today. I'll make it a fun one. You're a dedicated and accomplished musician. I'm curious if you see music as a refuge from your professional life—you want to keep those worlds separate—or are there connecting points that make both more enriching and fun for you?

ASIMOW: Refuge. I'm sure there are connection points, but I don't spend time dwelling on them. No, it's another thing I do. It's another side of my character. It's another skill that I have developed over time and try to nurture and improve on, but I've not encountered too many situations where my knowledge of music has informed the science that I do or the other way around. I'm going to vote refuge on that.

ZIERLER: [laughs] Okay. Well, this has been a terrific initial conversation. Next time we'll go back—family roots, Southern California, and even before that. We'll go from there.

ASIMOW: Okay.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Friday, April 21, 2023. It's great to be back with Professor Paul Asimow. Paul, thank you for having me again.

ASIMOW: You're welcome.

From Eastern Europe to Southern California

ZIERLER: Alright, Paul, today what we're going to do after our first conversation—we did a wide-angled lens of your approach to research, the things that are interesting to you in the field. Let's go all the way back to the beginning. How many generations back in your family can you go to give sort of narrative context? Could we go back to Eastern Europe, I might guess?

ASIMOW: We can. I'm purebred, 100% Ashkenazi. My father's family is from Ukraine, my mother's family from Belarus, and I know quite a bit about my family background relatively speaking because my great-grandfather, Harry Asimow, wrote an autobiography when he retired at 65. He put it all down and self-published it and gave all his descendants a copy. He then lived another 30 years—

ZIERLER: Oh, wow.

ASIMOW: —and had a remarkable life, and we'll get into that. But from that I know a fair bit about where the Asimow name comes from and what his life and what his parents' lives were like in the old country.

ZIERLER: Do you know if it was Asimov in the old country?

ASIMOW: It is, yeah. The spelling Asimow, with a "W", is a pure one-time accident of Ellis Island procedure. Most other people with the same name ended up with Asimov. As far as we know, all Asimovs come from the same village called Petrovici, which is right on the line between Belarus and Russia. There is also an Azeri name that is spelled and pronounced exactly the same but is etymologically distinct.

ZIERLER: Okay, the Azeri Jews?

ASIMOW: Yeah. I've also done a fair amount of genealogy work. My mother happened to do a fourth-grade family tree project when her grandparents were alive, so I at least have names and birthdates and some general information that's complete back about three generations and in places goes back further. Mostly, I feel affinity with my father's side, and the Asimows in particular, just because that was a very close and large family when I was growing up, and I knew all of my great aunts and uncles and my great grandfather, and have those stories. So, yes, I have lots of other ancestors on my mother's side and my paternal grandmother's side, but—

ZIERLER: Your father's side was in Southern California when you were growing up for the most part?

ASIMOW: Yeah. We've been here for quite a while. So, we'll be systematic about it. My great grandfather, who in English goes by Harry Asimow, in Russian Gospodin Asimov—although, he never spoke Russian if he could avoid it—he was born 1880, in Ukraine. His father, Meyer Asimov, left home, left this village Petrovici, where the Asimov name comes from, as a young man to go out and work building roads around Ukraine and never came back, and met his wife in a small village a couple hours from Odessa. He had his family there, went back out on the road and died of cholera in a quarantined work camp. My great great grandmother went out, recovered his body, spent all her money giving him a Jewish funeral, and then had to leave her hometown and move to Odessa. That's where my great grandfather mostly grew up from 12 years or so on. He was pretty well educated by local standards and was able to make a living as a private tutor teaching Russian to Jewish kids that otherwise only spoke Yiddish and needed Russian to get by in the professional world. He apprenticed and became a sheet metal worker. Then, while he was in the army, posted in Poland, got very active in socialist propaganda and organizing, was a very committed socialist for his whole life, did a lot of illegal and dangerous stuff with the distribution of literature and back in Odessa, managed to land in prison several times. He tells the story that he got out of prison in the middle of an economic downturn when everybody was unemployed, and everyone was hungry, and the city couldn't really figure out how to feed anybody. He said, "Let me get my trade unionists together, and we'll build a soup kitchen, and we'll have it open by tomorrow." And he did.

ZIERLER: Wow.

ASIMOW: But come 1905, it just wasn't a good time to be a known labor union organizer in Ukraine, and he married his girlfriend, and they got on a dogsled across Finland and left and came here. His brother was already in Milwaukee, so they headed for Milwaukee upon landing. And then—

ZIERLER: How did he get there—the brother?

ASIMOW: The usual way, you know. The country was open to immigration in those years, and everybody was leaving if they could. I don't have many more details about when exactly the brother immigrated or why by the way of Milwaukee.

ZIERLER: Do you know what his work was?

ASIMOW: No. So, my great grandfather was, by inclination, an organizer of people. He kept trying to organize trade unions in Ukraine. He got here and he kept opening metal shops and trying to organize them along various utopian socialist lines, and everyone would rob him, and he'd go out of business. This happened repeatedly. There was a great story of that. He had a small shop in those years, in Chicago, and a woman came to him with a design for a laundry plunger. If you had your laundry in a laundry basin, and you needed to agitate it, she designed this plunger and asked him to make a few. He made her a few and she sold them, and she said, "Okay, I want you to make more." So, he made more, and she sold them. She said, "Okay, I want you to move to New York, rent a factory space, hire people and machinery and gear up to mass-produce these things." And he did. He moved his family to New York, rented a space, bought all the machinery, geared up to make these things, and then it turned out she was selling them through an illegal pyramid scheme, and she got shut down, and he was left holding the bag. That's when they moved to Los Angeles. That was about 1920.

ZIERLER: Oh, wow. That's early. Do you know where they landed in L.A.? Eastside?

ASIMOW: Eastside, sure; Boyle Heights. They had a shop called Central Metals on Central Avenue south of downtown in what's basically Skid Row now. It's a really, to me, classic American immigrant success story. My great grandfather was working class, came here, had four sons. They all went to college. They all became professionals. My oldest uncle, Morris Asimow, got a PhD from Berkeley in mechanical engineering and metallurgy and had a career as an engineering professor. The second boy in the family, Charles, was an insurance agent. The third one, my grandfather William, was an accountant. The fourth one, Nathan, the youngest, was an attorney. All of them got where they got basically because of the University of California, which was open to everybody and essentially free, and was a path up the social ladder within a generation for people that had the talent and the drive. So, my four grandparents—there's this kind of process of diffusion, at least if you arrive from Eastern Europe and New York and you end up in California—they landed and they spread out across the country wherever they had any contacts. So, my four grandparents were born in Chicago; Binghamton, New York; South Bend, Indiana; and Omaha, Nebraska, but by the time my parents were born, the family was here in Southern California and stayed here for a couple of generations. Although now, I'm just about the only one left. My brothers and sisters and my father have all moved up to the Bay Area.

ZIERLER: Your mom's family was in Southern California also?

ASIMOW: Right. My mother's father was born in South Bend, my mother's mother in Omaha. My mother's mother's father—that's the Katzman side—the Katzman brothers set up a furniture manufacturing company in Omaha and had considerable success. The company is still there. It's called Mastercraft Furniture. Sometime around 1920, my great grandfather developed respiratory problems from working in a sawmill and being covered with dust all the time, and his doctors said, "You need to move to a dry climate."

ZIERLER: Classic story.

ASIMOW: Conventional treatment for lung problems then. So, he went to his brothers and said, "Well, I have to move to California. I'd like you to buy out my share." And they said, "Goodbye." And so, my branch of the family never talked to the Omaha Katzman's again until 75 years later when I found them through the internet and, at least, filled in the family tree. I asked my great aunt, the oldest daughter on that side, "Tell me about the Omaha Katzmans." And her answer was, "Why do you want to know about them? They're terrible people."

ZIERLER: [laughs]

ASIMOW: [laughs] But as a result, yes, that side of the family was here by the twenties also.

ZIERLER: Entirely secular? Any religiosity on either side of the family?

ASIMOW: Not in that generation, no.

ZIERLER: This was an assimilation mode kind of situation?

ASIMOW: As far as I know, they were all already secular before they came here. They lived in the shtetl, but—well, my great grandfather does describe being sent to a cheder as a boy for a Jewish education and despising every minute of it and sort of describes the rabbis that taught there as sort of the same way that someone who went to Catholic school would describe the nuns. So, no, they were all secular, ethical humanists, socialists, and very committed to it. But everyone was Bar Mitzvahed and went to Hebrew school. But when Reform temples came along, that seemed to be the right level of commitment for some of us. My youngest great uncle on that side, my grandfather's younger brother, was very into building his own liturgy of secular humanism, and we had these alternative Rosh Hashanah parties and alternative seders that he wrote the text for that were very interesting and we got together for every year. These four brothers and their offspring settled here in southern California, and it was a very close family. We had both Jewish and secular holidays together every year, and so I feel very close to all of those cousins and have a lot of affinity with that family. This story of immigrant success and public university education and ascent into the middle and professional and almost leisure classes within a few generations is a story that's very close to my heart, and when I see modern examples of either people unable to immigrate to the United States, or able to immigrate but all the barriers that are put these days to assimilation or to education or to social mobility, it really bothers me. I would love the door to be as open now as it was for my family.

ZIERLER: Your parents grew up on the Eastside or they were part of that westward movement in Los Angeles?

ASIMOW: East. The westward movement came a little later. My dad grew up around Silver Lake, Los Feliz; my mom in the Baldwin Hills, which I guess is pretty far west, and Burbank, actually. Her father, my grandfather on that side, he's the one who had heart disease and died when I was one year old, so I don't know him very well. He was in food service. He worked for Carnation until they decided they didn't want any Jews, and then for S.E. Rykoff, which was a big restaurant food service company of the day. I guess Carnation was up in Burbank and Rykoff was down in Culver City, so that's where they were. My dad went to Marshall High School, which is in Los Feliz. My mom went to Dorsey which is Culver City-ish.

ZIERLER: This would have been upwardly mobile middle-class childhoods for both your parents?

ASIMOW: Yeah, absolutely. They both went to UCLA.

ZIERLER: Is that where they met?

ASIMOW: No, my dad may have been at UCLA; my mom was still in high school, I think, when they met. Then she went to UCLA and then he graduated—he's three years older—and went up to Berkeley for law school, and then she transferred to Berkeley and finished her degree there.

ZIERLER: Your father became a lawyer?

ASIMOW: Right. His father wanted him to be an accountant. He found it completely dull. I think his undergraduate major was accountancy, but then he went to law school, became a lawyer, and I think envisioned—I'm sure my mom envisioned—a career as a law firm kind of lawyer. But my dad never really liked practicing law and started teaching within a few years of graduating from law school and spent his career as a professor of law at UCLA.

ZIERLER: Oh.

ASIMOW: So, UCLA has been a very important element of Asimow family history for quite some time. My grandfather on the Asimow side went to USC. He's the one Trojan in the family. My grandmother, my father's mother, Frieda Asimow, née Frida Miller, went to UCLA in the first graduating class from the Westwood campus, class of '33. Got a degree in music right in the middle of the Depression. The only job she could find was teaching music at Maricopa Middle School up in the oil patch in the Central Valley, and she commuted back and forth over the old Grapevine in a 1929 Model T for several years. [laughs]

ZIERLER: [laughs]

ASIMOW: There's a great story about that. My grandmother happens to have been blonde and had blue eyes, and she showed up for this interview at this school in Maricopa, decided to wear gloves so she didn't put on nail polish, and when the principal asked her her religion she lied and said she was a Southern Baptist. It turned out he only hired blondes with blue eyes who didn't wear nail polish and were from sufficiently conservative sects of Protestantism. [laughs] So, she got that job. Then, my grandfather's oldest brother, Morris Asimow, after working as a metallurgist for a while, became the first professor of mechanical engineering at UCLA. And then, my father got a job there in the law school. And then, his first cousin, Leonard Asimow, was an assistant professor there in the math department for a few years. He ended up spending most of career at the University of Wyoming. Had I gone to UCLA, I would have been the fourth Professor Asimow in the history of the institution. [laughs]

ZIERLER: [laughs] That might be a record.

ASIMOW: Yeah. And I should mention that my father's first cousin on his mother's side, Ray Orbach, was also a UCLA professor and provost—

ZIERLER: Yeah! I know Ray.

ASIMOW: —to DOE and all the other things that he's done.

ZIERLER: Yeah!

ASIMOW: Yeah, so Ray is my father's first cousin.

ZIERLER: Oh, wow!

ASIMOW: Yeah, UCLA has been a big part of family life.

ZIERLER: What law did your father teach?

ASIMOW: His research specialties were mostly in administrative law, but he taught tax and contracts and administrative law, and later in his career, more or less for fun, he and a colleague, Paul Bergman, wrote a book about lawyers in movies and kind of a guide as to what videos you should rent if you were interested in trial scenes in movies, called Reel Justice. But he parlayed that into something of a research and teaching specialty in the concept of law and popular culture, exploring, sometimes with law students, sometimes with undergrads from various majors, the extent to which popular culture shapes perceptions of the law and lawyers, or vice versa. He's now 83. He retired from UCLA, and he moved up to Stanford, and he got a sort of part-time teaching position there that was a three-year contract, but the dean changed and the new dean didn't know it was short-term contract, so he spent ten years at Stanford [laughs] teaching contracts or administrative law or popular culture or whatever they needed. Finally, Stanford realized that he wasn't supposed to be there [laughs] and brought that to an end. And then, he wasn't ready to stop, so he got a job at the University of Santa Clara teaching, again, first year Contracts and Law and popular culture.

ZIERLER: This is a man who loved to teach.

ASIMOW: Loved to teach. Taught virtually through the pandemic, although he really didn't like it very much. I think, now, he's about done. He's just doing the law and popular culture seminar, and I'm not sure he likes teaching at Santa Clara as much as at Stanford or UCLA because frankly, the students are too nervous about passing the Bar which doesn't make it as much fun to teach them.

ZIERLER: Did your mom work when you were growing up?

ASIMOW: Yes. I don't think it was ever her intent to work, but my parents divorced when I was three—about 1972—and after a couple of years, my mom went back to school and got a degree in technical photography and became a medical photographer and worked at St. Joseph's hospital in Burbank—oh, Cedar Sinai and then St. Joseph's, and then UCLA in the Neuropsychiatric Institute for the last twenty years or so, before she retired. Kind of gradually moving from actual photography into graphic arts as that's what the researchers there needed support for. And so, by the time I was in kindergarten, she was going to school, and by the time I was in grade school, she was working.

ZIERLER: Do you have siblings?

ASIMOW: Yeah. Slightly complicated California family. [laughs] I have one full brother, three years older. He is an attorney. He lives in Oakland, and his name is Daniel Asimow, and if you ask, apparently, ChatGPT to tell you about Daniel Asimow, it says, "Daniel Asimow is a professor at the California Institute of Technology," and tells you all about my research. [laughs]

ZIERLER: [laughs] AI has a way to go.

ASIMOW: Yes. My parents, while married, had two boys—my brother and me—and then they divorced. My father remarried a woman with three kids from her first marriage, so I have—although my stepmother is gone since 2006, I still consider them my stepsisters and stepbrother. So, I have two stepsisters and a stepbrother. They were all in the Bay Area until my stepbrother recently moved to Florida. Then my mom remarried and had a girl, so I have a half-sister 15 years younger than me who is a nurse and recently moved to Portland. Depending on how you count, I have somewhere between one and a half and six siblings.

ZIERLER: And growing up, did you shuttle between households?

ASIMOW: My mom was the custodial parent but we had the kind of standard arrangement of one night a week and alternate weekends with my dad, and they always lived pretty close together, so it was not a difficult arrangement. We also tended to do a lot of traveling with my dad, so a lot of my outdoor education, and I think a lot of the roots of what one day drew me to Earth science, came from camping trips with my dad. That wasn't something that my mom had the inclination or wherewithal to do very much, although we did travel with her sometimes. There was—still is—a family camp for Berkeley alumni called Lair of the Bear up in the Sierras. We went there several summers with my mom. So, yes, I lived with my mom, but I had a room at my dad's and went back and forth.

ZIERLER: In this rich family history you're providing, I haven't heard any science in the family. Was there any thread of scientific inclination going back?

ASIMOW: Yeah. My father's oldest uncle, Morris Asimow, was an engineer—a metallurgist—and actually liked perfecting, or developing, machine tools and had a machine shop in his basement that we visited a couple of times.

ZIERLER: Oh, wow.

ASIMOW: He would make randomly shaped trinkets for the kids that visited. So, that engineering strain goes way back. That was always there. His son, Robert Asimow, my father's first cousin, also a mechanical engineer, and he was around. My father's other first cousin, Ray Orbach, was a physicist. And my father's other first cousin, Leonard Asimow, was a mathematician. So, in my immediate family, no, there wasn't any science except my mom sort of idolizes doctors and medical science and certainly had it in mind that if one of her sons was going to be a lawyer, the other one should be a doctor.

ZIERLER: [laughs]

ASIMOW: I had to actively work against this project by avoiding biology classes assiduously, so as to make sure that I wasn't qualified for med school by the time I graduated college. [laughs]

ZIERLER: [laughs]

ASIMOW: She eventually got her wish when my youngest sister gave up her career in film and went back to school to become a nurse. My mom wanted to be a nurse, but her mom said, "Eh, that's menial work. You're just changing people's bedpans. Don't do that," and prevented it. So, yes, there have been scientists in the family, going back a generation before mine. And as you know, Ray Orbach went to Caltech.

ZIERLER: Have you ever visited Europe? The old shtetl?

ASIMOW: I haven't. My uncle Nathan did—that's my grandfather's youngest brother—went to Manistirshina, the village where his mom was born.

ZIERLER: Presumably, they were wiped out during World War II, those villages.

ASIMOW: Of course, yeah. So, I don't think they found anybody who really remembered his mom, and in Petrovici, the Asimow family village, my great great grandfather left town in like 1875 as a young man. Nobody remembered him when his son, my great grandfather—apparently to register for the draft you had to go to your father's home village, so he went home around 1900 and couldn't find anyone who knew his dad. There's a great story that Isaac Asimov recorded about this town. It used to be in Russia proper, and in 1845 when Czar Nicholas II expelled all the Jews from greater Russia and banished them to the Pale of Settlement, the big landowner in Petrovici, half of his workforce was Jewish, and he did not want to kick them out, so he picked up the border marker and moved it to the other side of town.

ZIERLER: [laughs]

ASIMOW: [laughs] And said, "We're in Belarus now." Or, whatever they called White Russia back then. And it stayed that way from 1845 until 1917 when the Soviets came through and surveyed the border and fixed it. So, sometimes it was in Russia and sometimes in Belarus.

ZIERLER: As far as you know, your entire family was out before World War II? Nobody was there?

ASIMOW: Right. Yeah, everybody, and all of their brothers and sisters were out by 1910 even. So, no, in my family there wasn't anybody close lost in the Holocaust. There wasn't any last-minute scramble to get out. And so, I don't have a lot of relatives in places that you could get to in 1930 when you couldn't necessarily get here. There's nobody in South America. There's nobody in Israel, except for much later migration.

ZIERLER: You went to public schools growing up?

ASIMOW: Somewhat. I went to public school for kindergarten through fourth grade—Roscomare Road Elementary School in Bel Air. Then, my fourth grade year—so that's like 1979, give or take—that's when LAUSD started bussing to try to desegregate the schools. The first semester of fourth grade I was bussed across town to a school, Queen Anne Place school, sort of near Crenshaw and Adams, I think, and I had a great experience there. I had a really good teacher who was perfectly capable of running her classroom at all necessary levels when suddenly having half a cohort of kids from this Westside school and half a cohort of kids from this Eastside school dumped together into one classroom.

ZIERLER: This was primarily a Black school?

ASIMOW: Yeah. And that was fine. And she just said, "Okay, you're the 12th grade spelling group. Here's a dictionary. Learn some words you don't know." Which was fine. The second semester of fourth grade we came back to my neighborhood school and they were completely shellshocked by having all of these remedial students and the teachers were not up to the challenge, I would say, of running their classrooms at multiple levels. Also, my fourth-grade teacher had just moved up from first grade, had been my first grade teacher and it was a completely wasted year. That's when I left the public school—a wasted semester, second half of that year—and transferred to Mirman School, which is on Mulholland, just a little bit west of 405. It's a private school K-8, test for admission, gifted students only. I spent two years there, the equivalent by age of fifth and sixth grades, and that was great, I think. It was a really good school. I made some good friends there. I learned a lot. I got very far ahead in math. But when it was time for middle school, their middle school program was very small—subcritical, even. When my brother went through, he was one of three eighth graders or something like that. And so, we applied to Harvard School, what is now half of Harvard-Westlake school. That's where I went to seventh grade and spent six years there and that was fantastic. It's a magnificent school and it was perfectly tailored to me, and they allowed me to accelerate in math even though they'd never done that before. I arrived, I looked at what they were teaching in seventh grade math and I said, "This is dumb. I've done this already. Can I take the final today?" They were a little bit taken aback, but they said, "Okay." Then they put me in eighth grade math. I went to my thirtieth high school reunion recently and people are still talking about this.

ZIERLER: [laughs]

ASIMOW: [laughs] But also, I went back to the school recently for a memorial service for a guy named Lee Carlson, who was the football coach and a math teacher there, and he addressed the problem that Harvard School had that they were one of the few places that would allow you to take BC Calculus as a junior. And then what? The best math students would run out of the high school math curriculum a year before they graduated, so he offered a class called Advanced Topics. It was kind of linear algebra, which, I think it's more commonplace now that everyone is in a race to get through the AP curriculum as quickly as possible, that a number of schools, especially feeder schools to Caltech, have something beyond calculus. It was pretty rare then. Anyway, I did that as junior. Then, as a senior, had to make up yet another math course and did a private tutorial in multivariable calculus. It was a really good school and really prepared me well. My brother stayed in the public school system, all the way through—University High School in Westwood. Also, my sister stayed in the public school system. She went to Palisades High School, Palisades Charter School. But for me, given how much I wanted to learn and the rate at which I wanted to learn it, private schools were better. So, yes, public schools as long as we could until it just wasn't serving my needs anymore.

Deep Musical Roots

ZIERLER: When does music enter the scene for you?

ASIMOW: Music goes way back in the family. My father's mother's father, Abraham Miller, was a bandmaster in Ukraine, played trumpet and violin and taught his daughter, my grandmother Frieda, to play the piano and taught her a whole catalogue of Yiddish folk music. She got a degree in music and had a career as a piano teacher, but also as an entertainer. She was the music lady at the Hollywood Los Feliz Jewish Community Center, putting together programs of Yiddish music for her generation where Yiddish folk music was a real thing and a way for people to bond. And even if the kids couldn't necessarily speak Yiddish, they could understand enough to appreciate the Yiddish songs. I like to explain her repertoire like this: if Klezmer is jazz based on Yiddish folk tunes, she just played those tunes straight. She just sang the words, accompanied herself on the piano. She made sure that her sons, my father and my uncle Steve, had piano lessons, and my dad is still a pianist. He has gotten very into it actually in his partial retirement, has been playing piano more actively. He and my stepmom have moved to a retirement community in the Bay Area, and he is playing piano for the community in the bar every Friday night and at the memory care center a couple times a week. Interestingly, my grandmother, my father, and my uncle, all have perfect pitch. I don't. I didn't get that gene. You don't have to have perfect pitch to be a musician. It's handy, but I can do without it. On the other hand, my father's perfect pitch has gone out of tune. Starting in his fifties, and progressing into his eighties, he has gradually gone further and further out of tune. It's perfectly precise, it's just inaccurate. If you play him a C, he will now, every time, tell you it's an A. He's three half-steps off, which must be really frustrating for playing the piano. [laughs] But he can still do it.

So, yes, there is this thread of music going quite far back on that side of the family. I started playing flute in sixth grade. Mirman School started a band program—or an orchestra program—and brought in a woodwind teacher and a brass teacher and a string teacher, and I picked flute as my instrument because I was inspired by Jean-Pierre Rampal and James Galway. I focused on flute and piccolo through high school. Harvard School had a small orchestra and a jazz band, and I played in those groups all six years. I probably should have upgraded my flute teacher earlier than I did. I was kind of loyal to this guy that I had been working with since sixth grade, but he didn't push me that hard. I think like a lot of adult musicians, I wish I had practiced more as a kid. But I was okay. Before going to college, I knew that I wanted to play in music groups in college, so I got a new teacher that summer to really prepare for auditions. I went to my first lesson, and he was like, "Eh. I don't like your embouchure. I don't like your stance. I don't like your left-hand position. I don't like your right-hand position. Let's rebuild." [laughs]

Up to that point, I was an orchestra musician. I mostly played classical music. I was in the jazz band, but I was never really good at it, and my school didn't have a marching band. It wasn't big enough. Well, I got to Harvard College, and Harvard has three undergraduate orchestras and lots of other music programs. I didn't get into any of them, except the Early Music Ensemble, the Gilbert and Sullivan Pit Orchestra, and the marching band. I also joined the Wind Ensemble because fall of my freshmen year, they were doing a concert with Peter Schickele, the P.D.Q. Bach guy, and I really wanted to be in that show. So, I joined the wind ensemble as a percussionist, eventually working my way up to playing flute in that group. I did a lot of flute playing in college, but I basically transitioned from being an orchestra musician to being a band musician at that point, basically because I wasn't good enough to get into Harvard Radcliffe Orchestra or the Bach Society, and the Mozart Society—which had previously been a freshmen only orchestra—the previous years' class voted to keep their seats. [laughs] And so there weren't any spots available.

ZIERLER: I wonder if you could explain the difference of orchestra and band musician.

ASIMOW: Oh, so orchestras have strings and—

ZIERLER: This is the big symphony?

ASIMOW: Yeah. Whereas bands have only woodwinds, brass, and percussion, and they can play either music that is written specifically for woodwinds, brass, and percussion, or transcriptions of orchestra pieces. Pretty much every orchestra piece that you can think of has been transcribed because in the early years of the 20th century, every town in America had a band, but only the big cities had orchestras. And so, the way people heard most classical music was in band transcription unless they happened to live in New York or Cleveland or Philadelphia or whatever. So, you can play classical music, although a lot of the original band literature is later. It's Romantic or 20th century just because nobody was writing original music for winds in the Baroque or Classical periods. But the Harvard University Band—the student run, somewhat undisciplined marching band—was really my home in college. That and Dunster House and the Geology Department, but most of my friends, most of my social life, was centered around the band. After about a year of playing piccolo in the marching band, I decided it was pointless, and I learned to play the tuba.

ZIERLER: That's an extreme size differential right there.

ASIMOW: [laughs] Well, you know, you're more useful to the group, and I could read bass clef because I'd played piano, and it was not a difficult transition.

ZIERLER: Ah, I was going to ask, when did you pick up piano? That was early on?

ASIMOW: That was actually before flute. I had had a couple years of piano. There was this very diminutive person, Jordana Bernstein, who was three years older than me, had come as a piccolo player and switched to tuba because the band needed tubas. But she could barely carry a fiberglass sousaphone. It was real work for her. [laughs] And so, during winter season, when the band walks down to the hockey rink for hockey games, I took to carrying her tuba for her down to the hockey rink and playing it along the way. I realized I could do it. And then, for like two years, every hockey game, as I was wrestling my way through the turnstile, the ticket-taker would say, "You should have played the piccolo."

ZIERLER: [laughs]

ASIMOW: I said, "Yeah, I do play the piccolo." [laughs] The Harvard Band is a student-run organization. There is a faculty director, but he does as little as possible. He keeps his hands off, and so there's a student conductor, and if you study conducting with the faculty conductor for about a year, you can audition to be student conductor. Also, the student conductor arranges all the original arrangements that the group does. I really wanted to do that. I thought that was how I could best contribute to the group. And so, I was conductor of the Harvard Band from the Yale game my junior year until the Yale game my senior year, such that when I got here for graduate school and I immediately went and tried out for Bill Bing's Caltech-Oxy Concert Band, as it was called then, he knew that I could play flute and I could play tuba and I could conduct, and started giving me the opportunity to actually conduct the Caltech Concert Band—sort of one piece on every show—since about 1991. So that's where that whole conducting the band thing came from.

ZIERLER: Let's shift back to high school. What did you do during the summers? Did you work?

ASIMOW: No, I went to camp. This was one of my ways to connect with Jewishness, was Hebrew school during the year and Jewish summer camp during the summer. I went a couple years, in middle school, to Camp Alonim at the Brandeis Bardin Institute in Simi Valley, which is an ungodly awful place in the summer. It's over a hundred degrees and there's tons of bugs.

ZIERLER: [laughs]

ASIMOW: [laughs] It wasn't that great. So, then I switched to Wilshire Boulevard Temple Camps, which are by the beach in Malibu.

ZIERLER: Ah, that's much better.

ASIMOW: And, I went to Camp Hess Kramer summer before, say, 8th, 9th, 10th grades as a camper, and 11th grade as a CIT and 12th grade as a junior counselor. Summer before college I did work. My mom still harbored the idea that I was going to be a doctor, and she managed to get me a job as a phlebotomist in the St. Joseph's Hospital Medical Lab. Which is a crazy thing for an 18-year-old kid to do with a few weeks of training. Also, we're talking about 1987. Phlebotomists at that point hadn't really internalized the idea of bloodborne pathogens, and it was still sort of like the older ones wouldn't wear gloves because they felt like they couldn't feel the vein with a glove on.

ZIERLER: Yeah.

ASIMOW: Weird time.

ZIERLER: The AIDS crisis—

ASIMOW: —was happening, yeah. [laughs] So, you should be wearing gloves.

ZIERLER: Oh, yeah.

ASIMOW: Anyway, I have a lifetime appreciation for a good vein as a result of that summer of experience, but—

ZIERLER: But that sealed the deal for you. [laughs]

ASIMOW: It did not succeed in drawing me into medical practice. But no, I didn't have to work. There was always plenty of money and not that much to spend it on. So, summer camp.

ZIERLER: Did you graduate at the top of your class? Or, what made it apparent to you that a place like Harvard was in range?

ASIMOW: Oh, so that's interesting. I mean, yes, I was valedictorian of my class, but everyone in my family went to university in California—mostly public university, UCLA or Berkeley or Cal State L.A.—until my brother who, against the advice of the college counselors at University High School, applied to Ivy League schools. So, my brother went ahead and applied to Ivy League schools and got into Harvard and was the first in the family to go back east for college. And so, three years later I come along and I'm going to a better high school, and I have better grades, and I have higher test scores, and I did more stuff, and so it was like, at that point—and now I was a legacy—anticlimactic when I got into Harvard. When my brother did, it was a big deal. They went around and showed the acceptance letter to everyone in the family. And then, younger brother comes along, and they go, "Okay, obviously, you're going too."

ZIERLER: And he's three years older, so you saw him—

ASIMOW: We overlapped for a year, yeah, which was nice. Because we didn't get along that well as kids. He's very competitive and kind of needed to prove his superiority all the time. [laughs] So, college was really when we had the opportunity to rebuild our relationship on a different basis.

ZIERLER: Did you apply early to Harvard? Did you apply to all the Ivys, kind of thing?

ASIMOW: Yeah, but I got in early to Harvard and pulled all the other applications.

ZIERLER: Coming into Harvard as a freshman, were you science-oriented at that point? Did you know that's what you wanted to pursue?

ASIMOW: No. At that point, I was still entertaining the idea of majoring in humanities or science.

ZIERLER: This is why Harvard over an MIT made more sense for you, for example?

ASIMOW: Right, and I should emphasize, as I often tell people, I had never heard of Caltech when I was applying to college.

ZIERLER: [laughs] That's great.

ASIMOW: I went to high school just 30 kilometers over there. My father's first cousin had gone to Caltech but didn't talk about it at family gatherings or anything.

ZIERLER: What about Linus Pauling or Richard Feynman—were you aware of these names, or any affiliation?

ASIMOW: I was aware of Linus Pauling because I took AP Chemistry but not of his connection to Caltech. And it was a little before the peak of Richard Feynman's pop culture fame.

ZIERLER: Right. Charles Richter? —Nothing?

ASIMOW: I know these people now—

ZIERLER: Right. [laughs]

ASIMOW: Sure. But no, it was not on my radar at all. There was one guy from my high school that went to Caltech; I don't know how he heard about it. But even if I had, I was looking for a liberal arts university or a liberal arts college and was thinking big university, and I'm glad that I made that choice. Yes, as it happens, I went into science very thoroughly by the time I was halfway through freshmen year, but I liked having all those other kinds of people around that you don't have at Caltech. Because yes, we take HSS classes here, but there aren't any English majors or literature majors or economics majors or people who think like that.

ZIERLER: I wonder if the mechanical engineers in your family had any interface with like Caltech. They must have been aware.

ASIMOW: Yeah? But, again, didn't know.

ZIERLER: Didn't filter down to you.

ASIMOW: Missed that.

The Legend of JBT at Harvard

ZIERLER: What year did you start at Harvard?

ASIMOW: 1987. I went there at least nominally saying that I was open to the idea of majoring in philosophy or physics, and then something very interesting happened. My brother had also gone to Harvard thinking he was going to major in physics and burned out on that very quickly. He became a social studies major. Social studies is an honors-only major at Harvard. You have to write a thesis and you can sort of draw classes and research advisors from any of the social sciences. But he said, "You know, science is more than physics. You should explore a little bit. Look around. Open your horizons." I pulled out the course catalogue and I found that my first fall semester I could take mineralogy. That seemed like exploring, so I did.

ZIERLER: Okay, so on that point, you've emphasized on a few occasions now, the importance of your father and outdoor adventures as it relates to geology, Earth science, things like that. So, when you have a love of the outdoors, that can go in any number of directions. Have you ever thought about why specifically that opened up a pathway in things like geology and minerology?

ASIMOW: It's just, in retrospect, I see that I had that appreciation. I had that comfort with the outdoors. I had the privilege to know that you can go out of cities and be okay and it's beautiful and there's lots to see, and I know a lot of people don't get that opportunity and it's hard for them to understand the attraction of Earth science coming to it at an older age. So, it was there, but at this point it was very implicit. I never thought until this mineralogy class blew me away with its awesomeness that I thought it would be something I would spend my life doing.

ZIERLER: Oh, wow. Who was the professor?

ASIMOW: His name is James B. Thompson, Jr. Such a towering figure in the field that people just called him JBT, and everybody knew what that stood for. He was a professor at Harvard for many years. His specialties were mineralogy and metamorphic petrology, and the class that he's most known for teaching was a graduate course in phase equilibria, in how you analyze the stability relations among minerals and magmas. This graduate level class was so famously difficult that graduate students at Harvard would typically audit it before they dared to take it. Ed Stolper took it as an undergrad.

ZIERLER: [laughs]

ASIMOW: And people that were there that year, 1974, whatever it was, like Charlie Langmuir who is now a Harvard professor—was my postdoc advisor—he was sitting in the back as a graduate student—describes the class as a one-on-one dialogue between JBT and Ed Stolper.

ZIERLER: [laughs]

ASIMOW: This is significant for a couple of reasons. One is that Ed wrote down everything that JBT said and then he went home each night, and he recopied it in four-color pen and made a perfect set of notes for JBT's phase equilibrium knowledge. And JBT never wrote a textbook, and it all just came out of his head and would have disappeared into the ether except Ed wrote it down. And when I teach phase equilibria, I use Ed's notes as a textbook.

ZIERLER: Wow.

ASIMOW: And nobody ever wrote this book until now. Ed and I are working on it. It's going to be a decade-long project to get it done, but this way of thinking about stability relations, this way of using the geometry and topology of phase diagrams, it's beautiful, and it's elegant, and we think it's useful, and we want to get it out there before it disappears. So, I didn't have the opportunity to take that class, but JBT also just taught intro mineralogy, and this year, Fall of 1987, was the last time he taught it before he retired. For me, it was absolutely transformative that you could take your knowledge of chemistry and your knowledge of physics and apply them to these beautiful objects—crystals and minerals—and understand their structure and the underlying symmetries and the relations between different mineral groups. And then you could go out and have a field trip just around the Harvard campus, looking at the fenceposts and curbstones and seeing the different granites and the crystals in them. Or, you could go up to Vermont.

ZIERLER: You had a strong enough background already in physics and chemistry to appreciate at an advanced level what that could mean for understanding mineralogy?

ASIMOW: Yeah. I had a really good AP Chemistry class in high school, really good. It's the last chemistry class I ever had to take, and I'm a geochemistry professor.

ZIERLER: Yeah. [laughs]

ASIMOW: I had both AP Physics, Mechanics and Electromagnetism; and I was taking Physics 55 which is the sort of upper-level freshmen physics class at Harvard. It's kind of the equivalent of Physics 12 here, except you don't have to take Physics 1 first. So, I had all of that because it seemed more likely that I was going into physics until this point when I suddenly discovered mineralogy and turned into Earth science. I like to say that taking that class and then committing to geological science as a major is the one surprising thing that I ever did academically. Everything else follows from that—going to graduate school in geology, getting a postdoc in geology, becoming a professor of geology—it all follows from that one turn.

ZIERLER: And this was truly happenstance, you just flipping through the course catalog and seeing, "Mineralogy, that looks interesting." Wow. And JBT was clearly an incredible teacher as well.

ASIMOW: Right. Absolutely.

ZIERLER: Animated in class?

ASIMOW: Yeah, very much so. And he had all these great visualization tricks, some of which a lot of people use and some of which were just his for teaching symmetry and the ideas of translation and reflection and rotation and getting mineral structures to find how you can transform them and get them to overlie on themselves. He used Escher prints because Escher was very into these same mathematical properties. He had this famous way of explaining a subtle difference in the sequence of stacking of layers in some minerals. It's just very hard to describe how the geometry of these layers is different unless you take the octahedral units that make up these layers and on the side of the octahedron that slants down you attach a duck neck and you talk about which way the ducks are flying. [laughs] And if the ducks are flying this way in one layer and this way in another layer, it's one mineral, and if they're all flying the same way it's another mineral. It's very hard to describe it except with the duck necks, and that was JBT's way of doing it. So, there are t-shirts from JBT's retirement symposium that have this octahedron with a duck neck on it, flying across the t-shirt. He had a lot of things like this.

ZIERLER: Administratively at Harvard, it's a department of geology? What's the umbrella?

ASIMOW: Earth and Planetary Science.

ZIERLER: Okay.

ASIMOW: It was already called that when I was there. I hear it was Department of Geology for many years before. Like many geology departments it changed its name to Earth and Planetary Science or something like that. It was a difficult time for the Department when I was there. Harvard has long had a fairly dysfunctional tenure and promotion system.

ZIERLER: Sure. They eat up junior faculty.

ASIMOW: Right. But being a junior faculty member at Harvard had no particular correlation with whether you would be a senior faculty member at Harvard.

ZIERLER: Right.

ASIMOW: Because when they're looking for a senior hire, they would literally send out letters saying, "Who's the best person in this field?" and maybe not even mention the person they were considering for promotion. So, during the time that I was there, trying to major in geology and take the necessary core classes, Jane Selverstone was denied tenure. Peter Williamson was denied tenure. Brian Wernicke left to come to Caltech. JBT retired, and it got to the point where this guy named Ray Siever was basically teaching everything. He was a sedimentologist, but he was teaching structural geology and sedimentology and mineralogy and metamorphic petrology. [laughs] He was the only one left. But I managed to take all the necessary classes from people before they gave up and left the place. Junior year I took a class in planetary science with a guy named John Wood, whose specialty was petrology of meteorites, but he was teaching a general planetary class. He had a joint appointment at the Smithsonian Astrophysical Observatory up on Observatory Hill, north of the quad. That planetary science class was really good, and I got interested in that, and I decided I wanted to do my senior thesis with him in planetary science. So, I got a bike so I could ride up to the Observatory all winter and it so happened that he was on the science team for the Magellan Mission to Venus because they needed people to think about the mineralogy and the chemistry of what was going on at the surface of Venus. And he seemed to be an appropriate person to be on that team.

Introduction to Mission Teams

ZIERLER: And now, finally are you thinking about JPL and Caltech? Is that on your radar yet?

ASIMOW: We're getting there.

ZIERLER: Okay. [laughs]

ASIMOW: Magellan got to Venus in August of 1990, and I needed to turn in a senior thesis by May of 1991. So, I actually came out here to—I think I was home for the summer. I went up to JPL for Venus Orbit Insertion. That was the first time I visited JPL, and then data started to come back within a couple of months, and we looked at the very first data products that were coming out, and I said, "Okay what am I going to write about?" There's this very enigmatic appearance to a lot of the impact craters on Venus. They have these, what look like fluid outflows coming out of them and going downhill, and they're a very clear feature in the early radar images from Magellan. So, I decided I would write about those, try to figure out what they were and why they're there and why impact craters on Venus have these outflows where impact craters on other worlds don't. So, I did, and it was very independent research. It wasn't really my advisor's specialty. He got me access to the data and then I figured out what to do with it, wrote a paper. Then, I turned in my thesis, then I graduated, and it turned out that all the altimetry data released in the first six months of the mission were bad, and you really need to know the slope down which a flow is going to understand the dynamics of the flow, so I had to revise my work. Then I ran into mission politics for the first time because I was no longer affiliated with a member of the science team, and even when I had been affiliated with a member of the science team, I wasn't really supposed to be working on craters, and the cratering team tried to shut me out. They said, "I don't know who this guy is, but he shouldn't have access to the data." We had to go all the way to the chief scientist of the mission and eventually work out that I could revise the analyses of the craters that had been already mapped while I was an undergrad, but I was not to look at any new craters that had been discovered since I graduated. [laughs]

ZIERLER: [laughs] You were grandfathered in with the old data?

ASIMOW: Yes, and so at that point I made an executive decision to stop doing planetary science and being involved with missions and depending on other people to generate data and turned entirely into terrestrial Earth science for a couple of decades. But stepping back a little bit, when I was shopping for graduate schools during my senior year, I wanted to find schools that had both planetary science and terrestrial Earth science in the same department where you didn't have to pick one when you applied to the PhD program; you could keep doing both. And that narrows the field to about six schools.

ZIERLER: Off the top of your head, what's similar to Caltech in that regard?

ASIMOW: MIT, Brown, Cornell, Washington University, UCLA, Berkeley. So, those are the places I applied for graduate school.

ZIERLER: Because you wanted one foot in, even though you were turned off by this experience—

ASIMOW: Well, that didn't happen yet.

ZIERLER: Oh, I see, right. That was later.

ASIMOW: Yeah, so we're talking when you're applying for graduate schools. This is fall of senior year, early spring of senior year at that point. I was still into planetary science. So, I was admitted by all those schools, and I visited them all. The first two Caltech professors that I met, John Wood was able to introduce me to Tom Ahrens when he came to Harvard for a Meteoritical Society meeting, and then, John also flew me to the Lunar and Planetary Science Conference in February, and there I met Gerry Wasserburg. So, the first two Caltech professors that I met are two famously obnoxious individuals. [laughs]

ZIERLER: [laughs] Yeah.

ASIMOW: But great scientists and great salesmen. They did a nice job talking up Caltech. Then I came here during my graduate school visits to see where I wanted to go, and Dave Stevenson and Ed Stolper pitched me a really interesting experimental project relevant to any terrestrial planet, not necessarily just to the Earth, and transmitted this vibe that I got almost uniquely from Caltech and that has not left me to this day, that the graduate students—at least me, with my pedigree and my self-presentation—they treated me as a colleague and said, "You're here to do research. Do your research, and we'll support you and see where it goes."

ZIERLER: What was the project that Stolper and Stevenson pitched you?

ASIMOW: So, this is fun because it was really Stevenson primarily who was pitching it, and Stevenson is a theorist, but it was an experimental project. Later in my graduate career, I ended up switching to theory and working with Ed Stolper, who's an experimentalist, but the project relates to the dynamics of partial melting of rocks. For chemical and thermodynamic reasons, rocks don't completely melt. They don't just go from solid to liquid. They partially melt. They form some fraction of liquid, and then that liquid can segregate from the solid residue and migrate to the surface, and that's how we get volcanoes. But that porous flow problem of liquid moving along the grain boundaries of the solids left behind and getting out is a really interesting problem. We call it melt migration. And porous flow phenomena are generally described by two parameters—the permeability—which in Darcy's law is the constant of proportionality between the applied pressure gradient and the rate of which the fluid flows through the porous medium. It was developed by Darcy who was describing the public fountains in the city of Dijon and the hydraulic head from where the water was getting into the system. So, you need to know the permeability and then something that describes the rheology of the solid medium, whether it responds elastically, or viscously, to changes in the pressure of the pore fluid. Can it expand if the pressure of the pore fluid goes up, and if it does, does it do so viscously, by flowing, or elastically, by just expanding?

So, if you want to describe the rate at which melts migrate out of partially molten rocks, you need to describe the rheology of the rock in response to volume changes, and the permeability that governs the flow of melt through the system, and neither of those numbers was known. There are theories that allow you to guess, but it seemed like it would be exciting to try to actually measure it. That would involve taking some of the techniques of experimental petrology—where we partially melt rocks all the time, but we usually do it in a sealed capsule—figuring out how to do it in an open geometry where we could push melt through the system from one side of a partially molten rock to the other, know the applied pressure gradient and measure the rate at which the melt flows, and then we would know the permeability. And actually, an even better way to do it, is oscillate the pressure on one side of the partially molten region and watch the response of the pressure on the other side, and from both the phase shift and the amplitude ratio of those two waves, you can solve for both the rheology and the permeability. That's the idea. The equations for how to do that had been partially worked out for a related case but with different boundary conditions, so I needed to rederive the equations. It's the one and only time in my career I've ever needed to do Laplace transforms and complex analysis. It so happens that the equations that I'm talking about are right behind you if you look behind you.

ZIERLER: Oh, wow!

ASIMOW: We used to do our oral exams here using posters because we didn't have PowerPoint. [laughs] Those are the posters from my oral exam in the second year of graduate school in 1992.

ZIERLER: Oh, that's great.

ASIMOW: They turned up, when he retired, in Hugh Taylor's storage space, the posters from my oral exam.

ZIERLER: Oh!

ASIMOW: [laughs] Yeah, I would have lost them, but somehow Hugh held onto them, and so there they are. I actually built that experiment, that apparatus. They came up with the money and the freedom to just let me buy stuff, and I almost made it work. Almost. But I geared up for the first kind of full version of that experiment in February of 1996 and my oldest son was born on February 7th, and I shut down the experiment [laughs] to go and watch my wife have a baby. And then, experimental work was much more difficult.

ZIERLER: Sure.

ASIMOW: In parallel, through 1994 and 1995, I had been working on thermodynamic calculations, and so I built that into my thesis and the experiment never actually happened. But it was the pitch to be able to do that experiment, and just figure out how to do it and build this new apparatus that was the last hook that made it clear that Caltech would be a good place for graduate school.

Theory and Experiment on Melt Migration

ZIERLER: Stevenson and Stolper were presenting this as a way to co-advise you?

ASIMOW: Yeah. Stevenson wanted the answer, and Stolper knew how to get it.

ZIERLER: Looking back, how did that translate to their own research interests? What were they working on that got them to this problem that they presented to you?

ASIMOW: Stevenson did a lot of the foundational work in understanding melt migration and why it's an interesting and important problem, just doing the basic physics of multiphase flow in a viscously deformable medium. Stevenson, with his student David Scott, in the 1980s, wrote some foundational papers on this field. Dan McKenzie, at Cambridge, wrote the other, or even competing, foundational papers. This was important work because people used to kind of ignore the migration problem and think that as a rock is partially melting, the liquid is sort of staying there and equilibrating with the solid, and that's an easy problem to do experimentally because you can do experiments in sealed capsules and get the liquid to equilibrate with the minerals and hopefully find the right conditions where the liquid that you make looks like the actual volcanic rocks that erupt. But it never really works because actually the liquids start moving as soon as you start making them, and they never fully equilibrate with their source rock. Instead, what you get is a mixture of little increments of melt that have been extracted across a range of pressures and temperatures.

Once Stevenson and McKenzie pointed this out and the chemical evidence that this was happening started to become obvious in the late 1980s, this whole batch melting paradigm fell aside. People realized that you can't do one experiment and explain a volcanic rock. You have to do an ensemble of experiments across a range of conditions and then develop either a parameterization or a thermodynamic tool to integrate the results of all those experiments to actually make a prediction that might describe a real volcanic rock. So, Stevenson was working on the physics of that. Stolper had expertise in doing high-temperature, high-pressure experiments, and imagining ways that you could adapt the techniques to do this more dynamic problem. And then, we started working on the chemistry and the thermodynamics of this and what's the right way to actually build the numerical tool to take the results of all these various experiments and make meaningful predictions about what comes out at mid-ocean ridges, our original target. The physical theory of multiphase flow, which is important in lots of areas of geological and planetary sciences, but in particular this melt migration problem is something Stevenson was working on and realized that everyone was just guessing the parameters because there were no experiments, and Stolper had the experimental knowledge. So, it was a natural collaboration, and they needed a broad student with good math background, good physics background, interested in igneous petrology, interested in learning to do experiments, and get his hands dirty. And that just sounded great to me. It's what I wanted to do.

ZIERLER: To go back to Harvard, your physics curriculum, what kind of physics did you focus on? What courses were important to you?

ASIMOW: I took a full year, kind of sophomore level, physics course. Well, it must have been a year and a half because Harvard is on semesters, 55A Mechanics, 55B Electricity and Magnetism, and 55C Waves. A whole semester of waves, which I thought was great. Waves are a really interesting, unifying principle across many areas of physics, from phonons that allow you to understand the thermodynamics of solids to seismology to light to all kinds of things.

ZIERLER: Would you have overlapped with Ramsey and Purcell, or that's before your time?

ASIMOW: We used Purcell's textbook, but no, I didn't know them. My physics professors were Howard Georgi for waves, Karl Strauch for electricity and magnetism, and I can't remember who taught mechanics. I also took a Fun with Physics class, essentially, from Bill Press.

ZIERLER: Oh, yeah!

ASIMOW: Which was epic. The class at the time was titled something like, "The Physics of Nuclear Warfare and Nuclear Defense", but it was basically an order of magnitude physics class just applied to problems like submarines and aircraft and nuclear weapons, and then the Cold War ended, and they changed the name of the class to, "Widely Applied Physics." But yeah, I did have the opportunity to take this class from Bill Press, and it was great.

ZIERLER: He was coming in from the Observatory for that?

ASIMOW: Yeah. When you read Numerical Recipes, the voice that makes that book so distinctively useful is very similar to the voice that was teaching in that class. I also had the opportunity to take an outstanding history of science class, History of Clocks and Telescopes, that met in the Harvard Collection of Historical Scientific Instruments in the basement of the science center, and it was co-taught by David Landes, who is a social scientist that studies the history of timekeeping and its influence on society and culture; Owen Gingerich, who's an astronomer who specializes in the history of observing and telescope construction; and Will Andrewes, who's the keeper of the Historical Scientific Instrument Collection at Harvard and had previously been the clock master at Greenwich Observatory. That was a really cool experience. We got to check out actual historical scientific instruments for a final project to try to make a measurement. I sat out in the courtyard of Dunster House all day with a pan of water and a 17th century sextant and measured the longitude of Harvard college—

ZIERLER: [laughs]

ASIMOW: –to the nearest second or something like that [laughs] before you could just do it by whipping your phone out and using GPS. So, those were the physics classes I took.

ZIERLER: Then math was part of physics, or you did a lot of math also?

ASIMOW: Not a lot of math, but this is interesting—Caltech requires everybody to take Math 1a which is a completely useless class. It's proof-based calculus. You learn mathematics the way mathematicians think of it, but you don't really learn— it's called calculus, but you don't learn the calculus that you need to actually do anything.

ZIERLER: This is pure math.

ASIMOW: It's pure math, right. And we insist that all Caltech students do it for one quarter. I took the comparable class at Harvard because I was still thinking, "Oh, maybe I'll be a math major." It's called Math 25 AB at Harvard, and people who are thinking of being math majors take it rather than Math 1 if you just need calculus or Math 21 if you need multivariable calculus—the practical math classes. So, we spent a year doing proofs, and it's a very Caltech-y kind of class. It's all organized around study groups; people work together collaboratively. It's very hard. It was very abstract. It was really fun. I had a great study group working with this guy that I'd spent several years losing to at math competitions around Southern California when he was at Palos Verdes High School, and I was at Harvard School. I loved it, but it helped me know that I wasn't going to be a math major, that I would do that for a year and then stop. So, I took this pure math class freshmen year for fun, basically, and exploration, and from that experience I kind of understand what the Caltech faculty are getting at and what the Math Department is getting at with Math 1a. In fact, we used Apostol's textbook for Math 25 at Harvard. I also took an applied math class, sort of partial differential equations and transforms and that kind of stuff, Applied Math 105. It's the equivalent of ACM 95 here. I had the good fortune to have a geophysics professor teaching it, so the examples were all drawn from geophysics, the wave equations that we were solving were for seismology, and the diffusion equation that we were solving was for terrestrial heat flow. That was a really useful class also because, for me, the person who happened to be teaching it, John Woodhouse, was relevant and helped me see how the applied math could actually be applied.

The chemistry part is interesting. The geology major at Harvard requires a chemistry class and most people just take Chem 10, which is introductory, inorganic chemistry. I didn't want to. I figured it would be full of pre-meds and competitive and difficult and I'd had this really good AP chemistry class, so I thought I knew all of chemistry. So, I waited until I was a senior and then I took quantum mechanics and statistical mechanics from the Chemistry Department which I figured would be mostly math and not really chemistry. I didn't get that much out of those classes, especially statistical mechanics. I didn't really grok it at that point, but I satisfied the requirement. So, it's a little bit ironic that I ended up being a professor of geochemistry here because I really kind of avoided chemistry as much as I could until I came to it through the chemistry of rocks and minerals and realized, "Well, they're made of atoms. You'd better understand how atoms behave if you're going to understand those systems." [laughs]

ZIERLER: [laughs] Paul, to go back, the prospect at Caltech was you were going to come here obviously as a student, but you'd be treated as a colleague; you're doing real research from the beginning. That was not the experience or the feedback you got looking at other programs? Caltech really stood out in that regard?

ASIMOW: Yep. Most other places I got the sense that you would get attached to a research project in progress and contribute to it rather than define your own from scratch and shape the whole problem and own it.

ZIERLER: That can cut both ways, though, too.

ASIMOW: Of course.

ZIERLER: That can be very daunting to a graduate student.

ASIMOW: I was not risk-averse at that time. I should also say I take advice and my undergraduate research advisor, John Wood said, "You should go to Caltech." Best advice I ever got. He was completely right.

ZIERLER: So, no other program was a close second, really.

ASIMOW: Not necessarily. I mean, I certainly gave Brown a hard look. I gave MIT a hard look. I gave Cornell a hard look. But I think, no, the outcome was pretty much foreordained that, partly because I was being pushed that way by my advisor, partly because I'd met and been impressed by a couple of Caltech professors, and partly because my visit here was really outstanding and eye-opening. Also, honestly, I wanted to come back home.

ZIERLER: Now that you knew where Caltech was, you were aware it was roughly in the Los Angeles area. [laughs]

ASIMOW: Yeah, exactly. So, no, it was not a hard choice. Certainly, it was the right choice.

ZIERLER: As you mentioned, it was important for all the programs that you looked at that there was the planetary and the geology together administratively. You had previously visited JPL. Was that an additional attraction in choosing Caltech? Did you see, at some point, that that might be an asset for your graduate experience?

ASIMOW: It was, absolutely.

ZIERLER: Retrospectively it was, but I'm saying the decision-making going in—

ASIMOW: At the time—yes. It was a few months later that I was like, "Blech. These planetary scientists. They're all about mission politics." That came after.

ZIERLER: [laughs] Yeah.

ASIMOW: No, that was definitely part of the attraction. I was admitted to graduate school here by the Planetary Science and Geochemistry options because I said I wanted to work on meteorites. When I got here and I realized that it was the geology students that got to do fieldwork, I switched my option to geology. So, my degree is in geology because, partly my research migrated to what's primarily a terrestrial problem, partly I decided I didn't want to work on missions, and partly I really wanted to do the fieldwork. And so, I did. So, my degree is in geology although my research is hard to categorize as geology or geochemistry or geophysics or planetary science. It's kind of all of those things.

ZIERLER: But that's kind of the point. That's how it should be, right?

ASIMOW: Right.

ZIERLER: On that note, I think that's the perfect narrative turning point to pick up next time when you actually start at Caltech as a graduate student.

ASIMOW: Okay.

ZIERLER: Alright.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Tuesday, May 2, 2023. It's great to be back with Professor Paul Asimow. Paul, once again, thank you for having me in your office.

ASIMOW: You're welcome.

ZIERLER: Today we're going to pick up where you've made the decision to come to Caltech. Let me start with a road not taken question. You explained last time you were going to come here. The plan was to work in meteorites. Then, you saw what mission politics was like; you wanted to be more involved in fieldwork. Did you ever circle back to meteorite research or was that truly something that got frozen in time at that decision point?

ASIMOW: I'm doing a lot of it now. So, there was a 20-year hiatus before I got interested again in meteorites, and the root was circuitous. My original interest in meteorites was the petrology. When small asteroids partially melt and separate into cores and mantles and even crusts, that's an igneous petrology process that happens under conditions different from melting on planets like the Earth—lower gravity, different chemical conditions. That was my original interest. Then, I went entirely into terrestrial igneous petrology, and how rocks melt on Earth and what happens, for graduate school and during my postdoc. But then, when I came back to join the faculty, I started working with Tom Ahrens and getting interested in shockwaves. One of the other things you see in meteorites is they are often strongly shocked because asteroids are always crashing into each other, and in fact if we have a piece that's small enough to arrive on the Earth without causing a catastrophe it must have been broken apart from a larger body at some part. So, essentially all meteorites have suffered some kind of collision. So, yeah, I came into meteorites through a different pathway of what they record in terms of shock events and my ability in the laboratory to simulate those shock events and learn something therefore about meteorites.

At the same time, as I started thinking more broadly about global geochemistry and the composition of the Earth and how we put together our estimate of planetary scale chemistry without grinding up the whole planet and measuring it, meteorites are where all that evidence comes from because they are pieces of planets surviving from the early solar system, or planetesimals, and they haven't been through as much complex processing over billions of years as terrestrial rocks. So, yes, I did come back to work on meteorites, not in graduate school but eventually, and I've also come back to work somewhat on planets. Through collaborations, or through the interests of my students, I've become involved in work on Mars. The original planetary science that I did as an undergraduate concerned impact craters on Venus, and now I've at least dedicated a week or two weeks to a KISS study project on a potential mission to Venus in the fairly far future because it's really a blue-sky concept that we were talking about.

ZIERLER: But this might be the next big JPL mission to go to Venus?

ASIMOW: Conceivably, yeah.

ZIERLER: But beyond your timescale?

ASIMOW: Well, I'm not that old. [laughs]

ZIERLER: [laughs] That's an optimistic answer.

ASIMOW: If this concept moves ahead, and I'm not sure that it will, it might be ready to launch about the time that I retire. It's not really what we're talking about now, but the problem with Venus is two problems. The surface environment is very inhospitable not only to life but to technology. It's 450 degrees C. It's 90 bars CO₂ pressure. It's very acidic. The Soviet Union actually landed several landers on Venus that operated for about 30 to 45 minutes before everything was fried. There are only certain measurements that you can make in 30 to 45 minutes. It's not a lot of time. On the other side, sample return from Venus is really hard. We haven't even managed sample return from Mars, which is a much smaller body with much lower gravity, and you can get off the surface of Mars with a much smaller rocket. So, getting something back from Venus, maybe that would be a great thing to do one day, but nobody's really talking about how to do it. So, the intermediate option to study rocks from the surface of Venus without bringing them back to Earth and without trying to do it on the surface of Venus is to do it on a balloon in the upper Venus atmosphere. About 50 kilometers up, the conditions in the Venus atmosphere are rather Earth-like. It's about 300 Kelvin and about 1 bar pressure. We know how to build technology that works at those conditions. So, the idea is, "Can we conceive of a mission where we get a long-lived aerial laboratory suspended from a balloon, or maybe a glider or something, that hangs out in the middle of the Venus atmosphere while we drop quick-sampling landers to the surface to grab something and come back up, rendezvous with the aerial lab, and do the analyses there?" Take a bunch of engineers from JPL and a bunch of scientists from Caltech and elsewhere and let them think about how that would work, if it would work, why it's worth doing, for a week; that's what this Keck Institute study project was about.

ZIERLER: Oh, wow. Well, now that we have a helicopter flying around Mars, it's like nothing is too far off the wall, I suppose. Why not? [laughs]

ASIMOW: I haven't actually published anything about Venus since my senior thesis as an undergraduate, but I'm still willing to think about it as an interesting place to go.

ZIERLER: Cool! Just a point of clarification, as you explained previously, your unpleasant surprise for the pervasiveness of mission politics, that steered you away from the meteorite research as a graduate student—

ASIMOW: It steered me away from mission based planetary science research, which meteorite studies are not. Meteorite studies, if you can get a sample, you work on it in your own lab very much the way you do with terrestrial rocks. So, it wasn't really the politics that drove me away from meteorites; it was just the particular problems that I happened to start working on.

ZIERLER: Got it. But you always wanted to do fieldwork—going outside with your dad, that was always— so, in some sense, geology was a very natural pivot because obviously you knew how much fieldwork would be involved in geology.

ASIMOW: It was. I'm not sure I realized it at the time that I had been raised to be preconditioned to love this kind of work and want to do it, but I was. I realize that now, looking back.

ZIERLER: As an undergraduate—we've already talked about the considerations why you chose Caltech—did geological and planetary science at Caltech loom large for you as an undergraduate at Harvard? Would you have come across the name of like a Bob Sharp, for example?

ASIMOW: No, it was entirely the doing of John Wood, my undergraduate thesis advisor, to introduce me to the place, to point out its history and how suitable it would be for me and the kind of work I wanted to do in the kind of way that I wanted to do it. Even when I came out here the summer before my senior year, to go to JPL for Magellan Venus Orbit Insertion, I don't think at that point I quite fully appreciated the connection between JPL and Caltech. When I was much later chairman of freshmen admissions and I came to discussions about Caltech's publicity problem and how do we make ourselves visible, certainly I understand that, because to me, even growing up not very far away, and even becoming a scientist, it was still invisible until it wasn't.

ZIERLER: All right, so, you arrive. What's the plan? Is it immediately that you're going to tackle this Stolper-Stevenson problem in tandem? That's the plan?

ASIMOW: Yeah. Just for background, the way the PhD program works here is pretty unusual, pretty distinctive. We don't admit students to be the student of a particular advisor. That is, the American model for graduate school is advisor-student match. The money comes from an advisor; you don't admit a student unless the advisor has money. It's pre-ordained at admission time. We don't do that. We believe very strongly that students are admitted by an option, or in my case, by the Division because I ended up changing options, and we insist that first-year students do two different projects with two different advisors on two different subjects for at least a year, even if they have a master's degree. The old-timers when I started would always point out that once upon a time it was seven different projects, or something like that, to prepare for your oral exam, and the fact that it was only two felt like [laughs] it had gone down a long way since the old days. One of my projects I already knew because it had been pitched to me when I was shopping for graduate schools, and I was interested in it, and I knew that it was a good project. That was this experimental attempt to characterize melt migration with Stolper and Stevenson. Then like most of our incoming students, I searched around for a second project for a few months before settling on one. The second project was jointly advised by Lee Silver and Hugh Taylor, looking at a distinctive and interesting rock formation that outcrops many places in Southern California with several different names depending on where you find it. In the outcrop west of Palmdale it's called the Pelona Schist. It outcrops underneath a major structure, a fault, that at that location is called the Pelona Thrust. This unit seems to be underneath everything in Southern California, although it only outcrops at places where there's been enough uplift to bring it to the surface, which are several places along the major regional faults.

The Pelona Schist is characterized by what we call an inverted metamorphic gradient. The preserved temperatures get hotter as you go up. Usually, they get hotter as you go down. In the Pelona Schist they get hotter as you go up until you get to the Pelona Thrust fault. So, that's interesting and we'd like to know why, and one of the ways we can infer the temperatures at which rocks reacted with water and the amount of water that might have migrated through them is looking at oxygen isotope ratios. This is a field of geochemistry that was pioneered here by Sam Epstein and then by Hugh Taylor. When I was here, Hugh was still active, at the height of his powers, and so, I wanted to learn that kind of research—both the fieldwork of going out and sampling in a systematic way to get the right kind of samples as a function of distance below the fault, and the structural geology of being able to reconstruct how far below the fault they were. Lee Silver was an excellent regional geologist. He knew the area. He also invited Perry Ehlig, who was a professor at Cal State L.A., who knew the area, to come out to the field with us once to introduce it. And then, also to bring the samples back to the lab, separate the quartz grains and the garnets from them, and working with Hugh Taylor and his student, Greg Holk, to extract the oxygen, and working with Sam to analyze the oxygen isotopes and put together a story about what we could learn about the rocks.

ZIERLER: What you brought back, you brought back to Silver's lab?

ASIMOW: Taylor's lab, to separate the quartz grains and fluorinate them. The way we analyze oxygen isotopes, you start with silicate rocks. The oxygen is tied to silicon atoms. It's in a solid. We want to do mass spectrometry on it. We have to get it into a gaseous state, so we react it with fluorine gas, which is very reactive, or sometimes with bromine pentafluoride. That breaks down the silicate bonds and liberates the oxygen, and then you react the oxygen with hot graphite to make it into CO₂ , and then you actually then analyze CO₂ gas where you've hopefully done it carefully enough that all the oxygen atoms came from the quartz grains, and you haven't fractionated them by the processing. So, you need a vacuum line with furnaces where you can load a few milligrams of your rock, let in fluorine gas, let it react for a while, extract the gas with a cryogenic cold finger, and then react it with the hot graphite, and then freeze it down into another cold finger as CO₂ where you can then take it to the mass spectrometer. Hugh Taylor had the vacuum lines up in the penthouse on the roof of North Mudd where if there were an accident with the fluorine it would only affect that one room and not the whole building. That turned out to be important in the Sierra Madre earthquake when that fluorine tank fell over and burst its regulator and flooded the roof with fluorine. Fortunately, it wasn't raining that day, so the fluorine gas just dispersed instead of turning into hydrofluoric acid on the roof.

ZIERLER: Ooh, yeah.

ASIMOW: But this is one of the reasons that the Safety Office here, correctly, is very strict about keeping your gas cylinders chained top and bottom because they will fall over in an earthquake. Anyway, Taylor had the fluorination lab, and then Sam Epstein had the mass spectrometer that we actually used to measure the isotope ratios and the CO₂ gas. Doing that project involved working with three of the great senior faculty at the time—Lee for the fieldwork, Hugh for the processing of the rocks and interpretation of the oxygen isotopes, and Sam for the actual measurement of the isotope ratios.

ZIERLER: Yeah, what great exposure for a first-year graduate student. What did you discover about yourself from each of those aspects of the research?

ASIMOW: Interesting. Doing the fieldwork with Lee certainly contributed to what I already knew—that I liked doing fieldwork, that I enjoyed being out there, and that I enjoyed learning from Lee. I also took a full GE121 advanced field geology course with Lee. We'll talk about that in a minute. I learned that just because your geology professor is much older than you, you should not necessarily offer to walk up the hill and drive the Jeep down to pick them up.

ZIERLER: [laughs] Right.

ASIMOW: That situation was solved when somebody else came along with a Jeep and drove us both up the hill.

ZIERLER: [laughs] Okay.

ASIMOW: Working with Hugh and extremely hazardous chemicals like fluorine, and with Greg Holk, I learned the importance of careful, reproducible, systematic standard operating procedures in the laboratory. I hadn't really done lab work before then, and if you want good data and if you want to be able to keep doing this kind of work and not get shut down, you have to be careful and systematic and do things right every time. So, that's really where I learned geochemical lab procedure for the first time. When I asked Sam if I could run the samples on his mass spectrometer, his reaction was, "Are you careful?" And I wasn't really sure how to respond to that question. How do I know if I'm careful? I said, "Well, I think so." That also was a very delicate instrument. This was an old mass spectrometer, kind of from the first generation of instruments that the geochemists here built themselves doing all their own glassblowing and all their own electronics. It was just about that time that commercial manufacturers started making mass spectrometers and selling them and putting them all in a box so you couldn't see all the guts, and Sam was never convinced that you could buy a mass spectrometer that was better than one you can build yourself. The world has totally gone that way now. Nobody builds their own mass spectrometers. If you want a workhorse instrument, you buy one off the shelf, and if you want to develop something new you work with a manufacturer. If you, at some point, interview John Eiler, you will learn about the process of designing a new mass spectrometer and then working with a vender to build it. But Sam's was home-built and so, like most home-built instruments, it was easy to break, and you had to operate it with some caution. I will also say, Sam Epstein had a special place in his heart for the Jewish graduate students and welcomed me very warmly as soon as I got here and had this kind of grandfatherly way of watching over the students. I didn't work that closely with him, but he was aware of my work, and he was one of the people who helped me feel welcome here, for sure.

ZIERLER: Did you feel firmly embedded on the experimental side at this point already? That was already going to be where you would focus?

ASIMOW: Yeah. That was my intent. A few years later, I moved into computational geology, but at that point certainly my intent was to focus on this experiment and that the experiment would be my thesis. The analytical project, with the fieldwork component, was a second project because you had to have two projects. That was definitely my assumption at that point.

ZIERLER: This happens in parallel with the Stolper-Stevenson problem? You're doing all of this all at once?

ASIMOW: Yeah.

ZIERLER: Wow.

ASIMOW: Yeah, this is what our first year of graduate school is like. You are doing two research projects that are hopefully totally unrelated to each other. You're also taking classes and going to seminars and doing all the learning, ideally, that you need to, within a couple of years, be ready to do your thesis. And so, you've taken all the classes you need for the background knowledge and skills. You've worked with your potential advisor for at least a year. You've taken your oral exam to show that you understand what the project is and why it's a good project and what you're going to do with it next. And then you do it.

So, yeah, the first year of graduate school is busy—a lot to do, a lot to figure out. One of the nice things about having two projects that are very different in style, like an experimental project and a field-based project, or an experimental project and a computational project, is the work habits involved in doing coding, versus the work habits involved in operating a laboratory, are very different and complementary. When the laboratory is stuck, instead of just sitting there and twiddling your thumbs, you can write some code. Or, when the program is executing, if you're doing some big calculation job, instead of sitting there and twiddling your thumbs, you can go and do something in the lab.

ZIERLER: Let's discuss the findings of both projects. We'll start with Stolper-Stevenson. What were some of the conclusions from that project?

ASIMOW: There were none because we didn't finish it at some level. One of the problems with experiments is they have their own schedule. You have to work the hours that the instrument may need you to work in order to do the project, and that turned out to be incompatible with parenting.

ZIERLER: [laughs]

ASIMOW: [laughs] So, I had this apparatus. I built it all up from scratch. I did a lot of test experiments on analog materials, on saltwater solutions instead of rock-magma solutions, at room temperature which is much easier, or water and little glass beads and things like that, and then just when I was about to do the real experiment, my first son was born and I literally turned the furnace off when my wife called and didn't get back to it for months. Then, talking about work habits and what you can do as a young father, the computational work was much easier, and I could see that it was definitely going somewhere. The experiment was probably going somewhere, but it was hard to work on it at that point and strategically not as obvious that it would lead to an influential thesis. So, I let it go. Eventually, somebody else did it, actually—a group at Woods Hole, or Brown, or MIT, or all of them, did a very similar experiment, eventually, about ten years later, which I've discovered is the statute of limitations on a good idea. If you don't write your own paper in ten years, someone else will write it for you.

ZIERLER: Was it worth someone else picking it up?

ASIMOW: You know, that paper hasn't, I would say, been all that influential. The quantity that we were trying to determine, fundamentally, is called permeability. It's the ratio between the pressure gradient and the flow velocity of liquid in a porous medium. There are theories for how the permeability should depend on the porosity, on the volume fraction that is liquid versus solid in the porous medium. It depends on the geometry, and the geometry in the magmatic case is very complicated, so you can't really do the problem analytically. So, we express the permeability as a power law function of the porosity, and the exponent might be anywhere between one and five and a half. It should be two for planar cracks and three for cylindrical tubes. Somebody calculated five and a half for the actual geometry. There was one experiment that had been done that almost measured this quantity and got an exponent of one which is very surprising. So, it's kind of wide open. Even though that experiment has now been published, people still, when they're doing the calculations, typically run both the exponent of two and the exponent of three because they say we still don't know. So, maybe the problem has not actually been solved. That was what I was trying to do, was measure that exponent and settle the issue. I learned a lot about experimental design and experimental technique that has proven useful to me over my whole career doing other kinds of experiments. Just the facility with high pressure plumbing, the facility with measuring high temperatures, the facility with data acquisition and capture, and a number of skills that I learned in the process of putting together this apparatus from scratch. The actual experiment never went anywhere. And that's okay.

ZIERLER: Sounds like your thesis went in a better direction anyway.

ASIMOW: It did, but what I was going to say is, it is nice to be able to have a few false starts and to be able to work on projects that don't actually reach an end point, and to be able to work on projects for a very long time before they do reach an end point. That is a luxury that not everybody has because graduate school is only so long, and a postdoc is only so long, and an assistant professor has to get tenure in so many years. For most people, for the first third of their career, they feel like everything has to yield a payoff really fast. Some projects will yield a payoff really fast and some won't. So, it is a luxury to be able to work on those and get away with it and not have it drag your career down. I feel fortunate to have been able to start lots of things and see where they go, pick which ones to finish, and still produce enough output that my talent has been recognized and my position is secure. Now, with tenure, I have all the time in the world to cogitate about things for a very long time.

ZIERLER: Picking which projects to finish, that's really a skill to learn, to figure out how to pick the winners.

ASIMOW: Yeah, right. And we kind of have this model of how it's supposed to work—that you have an idea, you write a proposal, if the idea seems promising then the idea gets funded, and then you do what you're supposed to do, and then you publish it. It doesn't always work that way, and it's nice when it doesn't work that way. Frequently, by the time an idea is mature enough to write a proposal, it's nearly done. [laughs]

ZIERLER: [laughs]

ASIMOW: That's the importance of seed money and things like the centers of Caltech and various other internal sources of funding that we have. Like the income from the GPS chair's leadership gift allows him to fund discovery projects, ideas that are not mature enough to compete for external funding but may be one day. That's one of Caltech's critical advantages is we have enough money and enough patience to nucleate ideas that seem crazy and wouldn't be competitive with most funding agencies and get them going until they are competitive. There's, I think, a lot of places where you just can't do that because there isn't enough seed money sloshing around. At some level that was my experiment in graduate school is, we never wrote a proposal to fund it, Stevenson and Stolper just had enough money sloshing around to set me up and see where it went. Didn't go anywhere, but it's part of the kinds of things that you can do at Caltech that you can't do a lot of other places, is take those risks.

ZIERLER: Now, the fieldwork experiment, was the major research question there about why the temperature rises as you go up? Was that the basic thing you were after?

ASIMOW: That is part of it. The other part of it is which way is fluid flowing through the formation. Is it going upwards towards the fault or downwards from the fault? Ultimately, one of the very confusing things about that fault is nobody really agreed on which way it moved, and that's important because if it's a thrust fault then all the rest of Southern California came from out in the Pacific and slid in on top of this schist unit of shallow oceanic coastal sediments, whereas if it's a normal fault then all the rest of North America is sliding off back toward the sea. And so you'd like to know whether it's a thrust fault or a normal fault. Part of that story is, were fluids coming down the fault and spreading out into the rocks around them? Or were they coming up toward the fault and draining to the surface along the fault? So, being able to trace the fluid flow direction is one of the things in addition to the temperature gradient that we would hope to get out of the oxygen isotope studies.

The result of that study that was most clear were the quartz veins. When the rock cracks and it's saturated with fluid, the fluid will precipitate quartz in the cracks and make quartz veins. And those gave very clear and systematic oxygen isotope results, getting lighter towards the fault which indicates increasing temperature towards the fault, which was the result we were looking for and was consistent with flow upwards through the formation towards the fault which, in my view, was most consistent with it being a thrust fault that was mostly bringing rocks in toward the North American mainland. Some years later, at another place in the Rand Mountains, working with Jason Saleeby, a student named Alan Chapman did a very nice thesis showing that actually the reason that it was ambiguous is that the fault first moved as a thrust fault with rocks on the top going inland toward North America and then later it slid back the other way. So, it was both. So, yeah, that was the main result there. I should say, in addition to working with Lee and Hugh and Sam on that project, we had a visiting professor, or possibly a Fairchild scholar, from Dartmouth named Page Chamberlain, who came and taught a metamorphic petrology class that I took, and he had what was at that time a very unique capability to fluorinate minerals and measure their oxygen isotope signatures using a laser at in situ spots rather than taking the whole mineral and putting it in a bomb and reacting it with fluorine where you lose the spatial context.

ZIERLER: What does that mean, losing the spatial context?

ASIMOW: Well, if I grind up the rock, take little pieces of the minerals, toss them in a reaction vessel, and react them in bulk, I can't look, for example, at the differences between the core and a rim of a given mineral grain because that's all been homogenized. If I make a polished section, and I come in with my laser and would make a small spot and work my way in toward the center of the grain, then I do have that spatial context. At Dartmouth, Chamberlain had a laser fluorination setup to do just that. A few years later, everybody had those. Hugh built one here towards the end of his career. I actually went and spent a week at Dartmouth analyzing the garnets, which are pretty large crystals, which can preserve zoning patterns, gradients in oxygen isotope ratios as they grow which would be complementary to what we could learn from the quartz grains which give just an instantaneous picture. That was another fun part of that project, more analytical skills that I learned and more ways to think about data and crystal growth and diffusion.

The Meaning of Great Field Geology

ZIERLER: Did Lee give you a Platonic ideal of what a great field geologist is?

ASIMOW: Yeah. Not just Lee. I had the opportunity to work with a number of what I consider to be great field geologists while I was here. Every graduate student in geology needs to take three advanced field classes from three different instructors, and we have enough field geologists that we can keep a circulation of different instructors coming through so the students can actually satisfy that requirement. I did advanced field geology classes with Jason Saleeby in the fall of my first year, with Kerry Sieh in the winter of my first year, and with Lee in the spring of my first year. They were all great, they were all informative, and they were all very different styles in the field. I also, importantly, had the opportunity to go on two or three short field trips with Bob Sharp.

When I got here, Bob Sharp had just turned 80 and everybody said, "You need to take Bob Sharp's field classes right now because who knows how long he'll keep doing it?" He kept doing it for another six or seven years. But the Bob Sharp trips weren't really so much about field skills as seeing the landscape and becoming familiar with it and just exploring. Those classes, the 136 classes, they're called, is a class that is just a field trip. Each student gives about a 15-minute presentation about some feature you're going to encounter on the outcrop. That style of class has survived. Joe Kirschvink took it over and has been doing it for years and years. Also, our spring break trip to Hawaii which Bob Sharp started is run in a similar style. It's just a really important part of our Division culture. It's a way to bring students that are not necessarily geology majors out into the field to get a taste of what we do. I think Joe Kirschvink's 136 trips lately have been running like 50 people. They take all the Division vehicles and go. Bob was still doing that himself when I started, and I did several of those trips with him. So, from all of these—

ZIERLER: Yeah, sort of like a composite sketch of what makes for a great field geologist.

ASIMOW: An appreciation for the complexity of nature and yet your ability to organize all the evidence available to you to tell a story that sees through the complexity. And an understanding that you can never really describe natural settings completely and thoroughly. You always have to choose the viewpoint that leads to a coherent story, and there's always rough edges, and that's okay. Apart from the appreciation of being outdoors and the importance of the problems that we study for society and resources and so on, this is one of the things that makes the difference, in my view, between geologists and a number of other areas of science, is that we're not trying to find complete analytical solutions that are provable and perfect. We are trying to find enough coherence to make a model that has some predictive power and narrates what happened at some level. Our catalog language about why you might want to be a geologist in the Caltech catalog hints at this kind of thing—that you need to appreciate complexity and incompleteness and difficult data sets. If you want the answer, you can go and be a mathematician or a physicist. And so, all of these professors understood and communicated that kind of sense of what you're trying to do when you grapple with a region. You can't tell the whole story, so you tell the story that you can tell, that you can defend, that you can support.

From Lee, the most important lesson that I think I learned is being systematic about your collecting. If you're picking up rocks and bringing them back, as soon as you pick it up, you have lost some context. It is no longer attached to the ground in the place that it came from, and that is important information about that rock. So, you record where you got the sample. You record as much as you can about how you sampled it and what it looked like before you sampled it, and you give it a unique number, and you never reuse that number for your entire career. And I keep working with geologists who send me samples whose numbers are like, "1", "2", "3", meaning, on that particular project or on that particular day it was the first, second, third sample they picked up, and after I've worked with these people for enough years, they've sent me 10 different samples that are all called number 1. And I keep trying to tell them, "This is not okay. Every sample you collect for your entire life has to have a unique identifier or you will mess up."

ZIERLER: So, for you the numbers just keep getting bigger.

ASIMOW: No, I have a code that is diagnostic of when I was there and where I was and then the order in which I picked it up. So, it takes more characters, but it prevents you from making dumb mistakes. Lee collected a lot of rocks over the course of his career, and he analyzed a lot of them, and he didn't publish a lot of that data, and it's still sitting down there in the sub-basement. Now that he's gone a number of his students and postdocs are coming back to say, "Can we publish this data that Lee and I gathered and Lee never published?" The fact that it never got published was a big problem, but it's easy for us to find which sample is which and extract that data, and even though Lee is gone, the information is still there, and we can still use it. So, this is one of my obsessions in geology [laughs] is curating a collection properly. In fact, after I graduated and went to Lamont-Doherty as a postdoc where they are much more connected with ocean-going expeditions, and I was invited to go on an expedition to the Lau Basin back-arc in the Western Pacific, I just kind of naturally took upon myself the task of naming the samples, organizing the collection, making sure that everything was traceable to which dredge it came from. And that was a skill I felt I understood and could do and wouldn't make mistakes. From Kerry Sieh, who is a somewhat different kind of geologist, he was studying neotectonics—the record of earthquakes and faults older than the seismographic record.

ZIERLER: This is what we call paleoseismology?

ASIMOW: Paleoseismology or neotectonics, same science. Too old for instrumented earthquakes and too young to look at bedrock contacts between different sorts of rocks. Looking at soil and alluvial fans and unconsolidated sediments and things, say, 100 to 10,000 years old. The bedrock geologists, who are studying the consolidated rocks, tend to refer to everything on top as overburden. Kerry would joke that beneath the rocks that he was studying there was underburden. [laughs]

ZIERLER: [laughs] That's great.

ASIMOW: Another thing I learned from Kerry is that the job of the most enthusiastic student in the field class, the one who's always walking right behind the professor, is to make sure the professor doesn't step on any rattlesnakes.

ZIERLER: [laughs] That's a good one.

ASIMOW: Lee took us to the same place that he took the Apollo astronauts and made sure that we knew it and made sure that we knew that although these guys weren't geologists, they were careful observers, and they could collect information and faithfully report it and be systematic about it and that if we, with all of our geological training, couldn't do as good a job as the astronauts then we weren't trying hard enough. I should say, I took field camp as an undergraduate, and I did these three advanced field classes, and I did this research cruise while I was a postdoc, but then I didn't do any other, in my career, field-based research for about 20 years. I did all laboratory and computational research, and I kind of forgot how much I like field research. I still ran field trips for my classes for teaching, but just kind of introductory sort of geo-tourism style field classes where you don't really engage with a region and try to solve unsolved problems. It wasn't until 2018 that I mounted my own field-based research project.

ZIERLER: Oh wow.

ASIMOW: In Baffin Island in Arctic Canada, which is just a gorgeous, exotic, faraway place. I was sitting there on a rock saying, "Oh yeah, [laughs] this is why I'm in this business, and also, I know what to do when I'm here. I know how to grapple with the region, where to go for samples, how to collect the samples in a way that's not destroying information." These skills that I picked up as an undergraduate and in graduate school all came back.

ZIERLER: The skill you just mentioned—where to go, the skill of scouting—how do you know? What did you learn from your mentors about where is interesting and what a preliminary trip might look like to identify an interesting place before making a big field trip out of it?

ASIMOW: Right. You start with what information is available from prior, often reconnaissance-level, mapping that may have been done there. If you can get air photos, you get air photos. Nowadays, if you can get satellite photos you get satellite photos. You read the literature which leads you to, hopefully, understand that an area either has not been studied in detail or has been studied in detail by two different groups that led to two different stories that need to be reconciled. So, you do your homework before you go to know why it's an interesting place to go to and what the questions are that you have in mind when you get there. If you're just doing reconnaissance-level work the point is just to get there, see what you think you see, write it down, and move on, and somebody will eventually come back and clean it up. Which is very useful, but it's a different mode and depending on how far out you go, most things have been studied at least at reconnaissance-level now.

Then when you get there, you start with a broad view of the area in question, and ideally you develop the instinct of looking around at things from a distance and saying, "That's a potentially interesting target. That's potentially an interesting target." Then you work your way down to the small scale of individual outcrops and individual hand samples that seem most promising for the problem at hand. So, if you're doing geochemistry on the rocks—so, you're bringing back the samples in order to grind them up and measure their composition or make a section and look at it microscopically—often what you really are most concerned with are fresh rocks, rocks that haven't been weathered or altered. So, you need to find bedrock outcrops. Most places, most of the ground is covered by plants, and even where there aren't plants, most places are covered by soil, and where the soil is worn away or eroded and you get bedrock exposures, most of it is weathered. This is especially true in the tropics. Last summer I did some fieldwork in Cameroon, tropical Africa, and this was especially true, that almost everything was vegetated or soil-covered or weathered, and most of the skill and most of the time was just finding fresh outcrops that had a chance of giving us information about what those rocks were like before they got close to the surface. It's a good reason to work in deserts if you can. There's not that much vegetation cover. Weathering is relatively slow because there's relatively little rainfall and it's easier to find fresh rocks and see all the relations instead of having to infer the relations from isolated outcrops. But you can't always work in the desert. Sometimes you have to go where you have to go.

In the case of the Baffin Island project, one of the primary reasons to go to these basalts on Baffin Island is they have the world's most exotic ratios of helium isotopes, which is thought to be a signature of rocks that are coming from the lower mantle. Helium isotopes can be messed up by cosmic ray exposure. Actually, cosmic ray-generated helium 3 is a thing you can measure if you are specifically interested in cosmic ray exposure and are trying to do surface dating. We were trying to measure the helium that was in the rocks before they were exposed to the surface. So, our priority was finding sheltered samples that ideally had not been exposed to the sun or the atmosphere or space for very long which meant going to the bottoms of cliffs and underhangs and places where there seemed to have been fresh landslides that exposed the surface behind. That's a particular style of searching for where the good sample's going to be. That's a short introduction to some of the considerations.

The Importance of Cultural Sensitivity

ZIERLER: What about administrative questions about public versus private land?

ASIMOW: Well, this is very important. Sampling is inherently destructive. You're taking pieces and bringing them back, and it needs to be done with permission of the landowners or the public agencies, and the indigenous people that have claims to ownership or stewardship of that land. And so, depending where you go, there are both ethical and legal considerations. And it takes time to do your research as to what permits you need and to get the permits, and beyond permitting, to develop a sampling plan that is environmentally and culturally responsible. Field geology has not always been that good at this. We are trying to develop better practices now. It's an active conversation we are having in the Division to get a set of policies in place and procedures so that when we think of a field project we want to do, one of the first things we think of is: Who do we need to ask to make sure that this is okay? And what do we need to do to make sure that we're not causing harm to the landscape while doing the science that we want to do? And how do we educate the tribe or the population or the federal agency or what have you about the fact that generally we're not there to exploit the landscape? We're not trying to make money off of it. We're trying to learn about it, which can be helpful for protecting it as well as enhancing its scientific and cultural value about how the landscape came to be there and explaining it. Typically with government entities, there is a procedure. You file the permit. They evaluate the permit. If it satisfies the rules, they give you the permit. With private landowners, and especially with indigenous people, it's much more about relationship building and trust building.

There was an incident a few years ago where a Caltech class was sampling on the Volcanic Tableland up north of Bishop without a permit on Bureau of Land Management land. Many excuses can be made that the BLM office was not responsive, their website was broken, they started the planning too late. Anyway, they went without a permit, and they were caught sampling without a permit, and they were ordered to stop. Then, the Bureau of Land Management hired an archaeologist to come and survey the site, and there were in fact petroglyphs not very far away. And so, a lawsuit was brought under the Archaeological Site Preservation Act—I don't remember the exact name of the law. It was settled. Caltech acknowledged that they were sampling without a permit and agreed to put a series of procedures in place so we wouldn't do it again, and to publish an article addressed to the rest of the geological community saying, "Here's how you do this right. Don't do what we did." So, just last weekend, I wanted to bring my class up onto the Volcanic Tableland near Bishop for something very short, very simple and totally nondestructive that probably didn't require a permit at all, but I made sure to reach out to the Bureau of Land Management and say, "I'm doing this. Can I get a permit?" And they actually sent an observer to watch me take these students out there for half an hour and just look at the rocks and then leave. So, we are working on rebuilding our relationship with the Bureau of Land Management Bishop office.

In the case of sampling—the Baffin Island expedition had two parts. The first part was in a national park, so we had to work with Parks Canada to make sure that they would permit what we were doing. The second part was not in the park, but Nunavut Territory is a part of Canada that is very much administered and managed jointly by the indigenous people and the Europeans, and so we worked with the local indigenous group to make sure that they agreed to what we were doing, that we were explaining ourselves to the indigenous people, and that somehow what we were doing would benefit the indigenous people. This can be done at a casual level, or it can be done deeply. We hired a man from the local people to come with us and be our bear spotter and see what we were doing, and we learned from him, and he learned from us. So, yes, this is a big subject, and one that all of our field geologists are thinking about with increased intensity of late.

ZIERLER: Have you run into a native people's flat rejection of a request? I'm thinking, for example, like the attempt to build the TMT on Mauna Kea. Are there analogs to that in geology for land being sacred, for there being neo-colonial tensions, that kind of thing?

ASIMOW: I'm sure there are. I have not run into that. For the small number of research expeditions that I have wanted to do in the places that I have wanted to go, no, I have not. I'm sure it has happened to many people, but not to me.

ZIERLER: The focus on faults in this project, did that give you any interface with the Seismo Lab? Was there any overlap there in terms of what they were looking at?

ASIMOW: Which project?

ZIERLER: The fieldwork, where you were explaining what's coming into California from the sea, what's going out.

ASIMOW: Oh, that one. No, that fault is extinct. It moved tens of millions of years ago, and so seismologists wouldn't be able to observe it from active seismicity. They might be able to map where it is from seismic profiling, but that wasn't really part of the project. I was just seeing it where it's exposed at the surface. So, no, that project did not involve interacting with the Seismo Lab. I have always been something of an outsider with respect to the Seismo Lab since I was not a geophysics major. Curiously, I run a lab now—the Shock Wave Lab—which is in the sub-basement of South Mudd, and Tom Ahrens, who built it, was a geophysics professor and a member of the Seismo Lab, but I am not. I have had several collaborations with Mike Gurnis, who is the director of the Seismo Lab but not actually a seismologist, and a few collaborations with Don Helmberger and his students, and Rob Clayton and his students, but I'm not a seismologist and have not worked hard to focus on projects that involve a lot of seismology.

ZIERLER: Amazingly, we're only still in year one of your graduate program. After all of this, how did you narrow your interests? How did Ed Stolper come to be your advisor?

ASIMOW: So, I did these two projects—one kind of designing and conceiving this experiment that I would do, and the other one picking up rocks from Southern California and analyzing them. It was still at that point, clearly my intent to keep building this experiment and doing it, and although Stevenson really conceived of the project and was the one that primarily was hoping to get a result, Stolper with his experimental derring-do was much more involved day-to-day in how I would build this thing and how it would work. So, he became my primary advisor. After my exam, I really focused entirely for about three years on designing this apparatus, buying the parts that I would need, testing it in a step-wise manner and building up toward the ultimate experiment. So, that was all going on, but then being in the Stolper group, what else was being talked about? What else was going on? Although he's primarily an experimentalist—at that time, late eighties, early nineties, experimental petrology reached a bit of a crisis, and the crisis was that we realized that you can't actually do an experiment that will completely explain the origin of a basaltic magma, that the process of making basaltic magmas is distributed over time and over temperature and over pressure, and basaltic magmas are mixtures of increments of liquid that have equilibrated at different conditions. Each experiment only equilibrates at a single condition, so you need to do something beyond just the experiments if you're going to understand the problem. In our reading group, I think it was a literature reading class led by Ed with a bunch of his students and students from the other petrology groups, we read a bunch of the attempts that were made at that time to build parameterizations, numerical models that took the results of many experiments and assembled them into—

ZIERLER: A story?

ASIMOW: A story. Using, more or less, arbitrary functional forms—polynomials or planes or cubic splines or whatever. Ed is a very insightful scientist. He read all these papers with us, and at the end of the term he said, "These are all taking the wrong approach. This is a thermodynamic problem. We should calculate these equilibria from a good thermodynamic model with functional forms that are informed by thermodynamic reasoning and not simply selected because they appear to fit the data." From that realization, Ed moved on to, "Okay, who's got such a model that could solve this problem?" The only one out there that we knew about was Mark Ghiorso's model.

Mark Ghiorso was, at the time, a professor at the University of Washington, and starting with his PhD thesis with Ian Carmichael at Berkeley, he developed a thermodynamic model that goes by the name of MELTS to describe equilibria among minerals and magmas. And so, Ed said, "Let's hire one of Ghiorso's students to come here as a postdoc and solve this problem of, ‘If you use thermodynamic models to calculate distributed processes of mantle melting to make mixed magmas, what does this model have to say about this problem?'" The student of Ghiorso that was hired to come here and be a postdoc and do this problem was Marc Hirschmann, and Marc and I started working together quite closely. He brought the code that drives Ghiorso's model with him, and so it was by no means an open source model, but I got access to the code because it came here with Hirschmann, and I started debugging it and finding problems with it and also trying to make it do what I wanted to make it do which was different from anything that Ghiorso had conceived that it could do. I didn't really have permission to do this, but by the time Marc Hirschmann informed Mark Ghiorso that this graduate student was playing with his code, I had found and solved a whole bunch of significant problems with the code and demonstrated my usefulness.

ZIERLER: Before you could get in trouble, you were going to get congratulated.

ASIMOW: Yeah, something like that. To hear Marc describe this period of activity from about 1994 to 1997, he failed to do what Ed had asked of him which was, in the course of one two-year postdoc, write a paper that would say everything there was to say about this problem. It turned out to be much too fruitful and productive a thing to finish in a couple of years and write one paper. It took more like 10 years and 10 papers. Some of those papers were my thesis and some where Marc was the first author. But this moment of insight that Ed had that this problem of going beyond single experiments and assembling them together to make a machine that could actually predict the output of complicated protracted processes over space and time in thermodynamic conditions, that you should do this with thermodynamics and not just arbitrary functions, that was a really key insight and that led to this whole body of work that supported Marc's career for many years and my career for many years.

ZIERLER: Paul, I want to go back to, if you could explain a little more—the crisis that you explained—was this sort of a gradual paradigm shift that things were more complex? Was there a landmark experiment that just really shifted people's perceptions? What started this?

ASIMOW: Yeah, I'd have to go back further than that. Starting in the late sixties, there were two persistent schools of thought about the origin of mid-ocean ridge basalts which are the most abundant igneous rock on Earth. They coat the entire floor of the ocean which is 70% of the surface of the Earth. It's an important rock to understand, and it should be the simplest rock to understand because there is no preexisting crust. When you pull the plates apart, you just have the mantle upwell and make fresh crust with nothing older to interact with, so it should be the simplest problem for us to understand. A school that followed more or less the pioneering ideas of Mike O'Hara, who was one of Ed Stolper's master's advisors, held that mid-ocean ridge basalts were derived by relatively high degree melting at relatively high pressure of relatively hot magmas that underwent extensive cooling, fractionation, and crystallization in the crust before erupting the liquid that you see.

There was another school of thought, more or less following on experimental work and ideas from Dean Presnall, who was a professor at University of Texas at Dallas, who held that mid-ocean ridge basalts formed at relatively low pressure and relatively low temperature by relatively low degrees of melting and that what was erupting was almost what was coming right out of the mantle with very little crystallization before erupting. And if you were thinking about this problem in terms of what we call batch melting, which is take your mantle source, equilibrate it at some pressure and temperature and melt fraction and there's your liquid—there are two almost degenerate solutions where you can do that at 30,000 bars of pressure or you can do that at 10,000 bars of pressure, you get two different liquids, but if you fractionate the one that was derived from 30,000 bars, it ends up coming to a final state that looks very much like the one that you get from 10,000. This debate went on for about 20 years without any real clear winner because the solution is really not apparent.

In the late eighties, two new ideas brought this debate to an end. One was thinking about how melts migrate, which comes back to that experiment I was trying to do. Papers by Dave Stevenson and by Dan McKenzie from Cambridge argued that at very low-degree melting, the melts start to move relative to the solids. They can segregate, and they can migrate, and therefore, they don't just sit there up to some final melt fraction, reacting with their residue and staying there in equilibrium with it. They leave. And that seems like it should be much be more akin to a fractional melting process than a batch melting process. The experiments are all batch melting. And if you can't experimentally do a fractional melting process then maybe you can't actually describe what's really going on.

So, the physical reasoning about the migration of melts and the rates at which they melt and whether they stay in equilibrium with their sources, that was one piece of information that came to light. The other was the advent of the ion microprobe or secondary ion mass spectrometer which is an analytical instrument that lets you analyze trace element concentrations at microscale. A group out of Woods Hole Oceanographic Institution led by Henry Dick and Nobu Shimizu, who was the ion probe wizard, looking at abyssal peridotites—which are a category of rock that you can find on the sea floor that are thought to be the residues left over after extraction of the oceanic crust—when you look at the abyssal peridotites, they do not look like residues of batch melting. The trace elements are too strongly fractionated from one another. They look like the residues of fractional melting from which melts are being progressively extracted and not allowed to react with the residue. So, we had the physical reasoning from thinking about melt migration and the chemical evidence from the abyssal peridotites which ought to be complementary to the basalts which is what everybody had been looking at before. Together, these brought an end to the, "Is it this kind of batch melting or is it that kind of batch melting?" debate because it isn't either of those things, and everybody realized you had to put together some story that could describe what happens in a situation where the melts are migrating, separating from their residue, and being mixed before fractionating and erupting.

ZIERLER: This was Ed's thermodynamic insight?

ASIMOW: Well, no, that came later. The insight that you had to do something led to a string of papers with various attempts to do this. Some of the earliest ones were by Charlie Langmuir who was then at Lamont, and his student, Emily Klein. There was another independent attempt to do this by Dan McKenzie and a petrologist from Cambridge named Mike Bickle. There was a student at University of Hawai'i at Mānoa named Yaoling Niu working with a petrologist there named Rodey Batiza. There was the MIT group led by Tim Grove and his student, Ro Kinzler. All four of these groups wrote independent papers that attempted to do this problem of calculating what you would get from a melting environment where the melts were separating from the residue and then being mixed. Those were the papers that we read in that reading group in the early nineties and tried to decide whether any one of them was best or whether they were all taking the wrong approach. The thermodynamic approach, which it seemed to us was the right way to do the problem—in principle, that is true. In practice, it's difficult. The thermodynamics is right in principle but it's always wrong in practice because the predictions that you make depend on the data that you have available to estimate quantities like standard enthalpies of formation of compounds and heat capacities and volumes and mixing properties. Even though it is true in theory that if you know the Gibbs energy of all the possible minerals and melts, the equilibrium will be the state of minimum Gibbs energy, it's a big "if" because knowing the Gibbs energy depends on all this empirical data, and the empirical data are incomplete and noisy. And so, you can build a good thermodynamic model; you can build a bad one. Just because you're using thermodynamics doesn't mean you're going to get the right answer. And knowing whether the answer is right is also challenging because you're trying to use it to make predictions specifically where you don't have experimental constraints.

So, the thermodynamic models that we built starting from Ghiorso's architecture made predictions, and some of those predictions could be tested against data and some of them could not, and there were clearly offsets. But even when things were offset from the right answer, because they were internally consistent you could look at trends that might be parallel to the real function even if it wasn't the real function. Anyway, because thermodynamic models can be wrong and they're very complicated and difficult to assess completely, this is another key thing that I learned from Ed, is try to do both a simple version of the model where you can understand what the model is doing completely, and the complex version that is more like the natural situation, and look for what those models have in common. That's what should be robust and what you can actually believe.

My first paper arising out of this kind of work, which is published in the Philosophical Transactions of the Royal Society—because the Royal Society held a discussion meeting and Ed went and presented this work, and so it got published in Philosophical Transactions—looks at, from a thermodynamic perspective, what happens as you're decompressing a parcel of mantle rock and it starts melting and it encounters a mineral-mineral phase transition. As a function of pressure, the mantle contains different minerals. As you're going up in pressure, you favor denser minerals which usually means rearranging the oxygen atoms around the aluminum first. Eventually, and much deeper in the mantle, rearranging the oxygen atoms around the silicon. But in the upper mantle, if you're going down, the stable assemblage for the first 30 kilometers is plagioclase lherzolite, is the name of the rock. Then there's a wide range from about 30 kilometers depth to about 80 kilometers depth where you have spinel iherzolite. The plagioclase reacts out and you make the mineral spinel. Then, from 70 kilometers or so down from there, you have garnet iherzolite, where the spinel reacts out and it makes garnet. On the way up, if you have an ascending parcel of garnet lherzolite and it starts melting, what happens when it changes to spinel iherzolite? And if your spinel lherzolite keeps ascending, what happens when, if, it changes to plagioclase iherzolite? If you look at the phase diagrams, the stability of these minerals and liquids as a function of pressure and temperature, there is what we call a cusp on the solidus (the solidus is the curve where melting begins). It's generally concave down but it has a cusp where it kinks back up at the intersection with the spinel-plagioclase transition and at the intersection with the garnet-spinel transition. Because there's a low point at the cusp, Dean Presnall, who was one of the participants in this lengthy debate about the origin of mid-ocean ridge basalts, argued that that cusp is the most likely place for most of the melt production to happen. It's kind of sticking down to a cold point on the solidus, and so if it the mantle was heating up, that's where the pressure-temperature profile is likely to intersect the melting point.

When I started running the thermodynamic models across this phase transition, I got a very unexpected behavior. You didn't get a bunch of melt at that point. It froze at that point, and it stopped melting; exactly the opposite of what Presnall had told us would happen there. I showed this to Ed and Ed said, "That's wrong. Go do it again." I did it again, and I got the same answer. Then we went to the Starbucks over there at Lake and California and talked for a while, and on the back of a napkin, Ed sketched a simplified model, the simplest model that we could think of that would have this behavior, and in that model it was clear to Ed, because he had been trained by James B. Thompson, how to think about this problem, that the decompression of a large parcel of mantle moving at centimeters per year, the independent variable that governs the energy budget of the system is not temperature; the independent variable is entropy. It is an adiabatic reversable process that happens at constant entropy, and the temperature is just an output. When you think of it that way and you realize that it takes entropy to drive the solid-solid phase transition, and therefore the entropy is not available to drive melting, you get the insight that actually what should happen at these cusps on the solidus is not melting but freezing—exactly what the complex thermodynamic model was doing. And then we felt that we understood it. We knew why the model was doing that. And so, we wrote a paper that showed in a one-component system, which is the chemically simplest system you can write down where you can draw complete phase diagrams on two-dimensional pieces of paper that show everything, it is obvious in the one-component system that if you have a phase transition like this, it has to cause freezing. Then we did the two-component system which is chemically a little bit more complicated but has behaviors that the mantle has because it's a solid solution. We can show that that system will also freeze when it encounters one of these reactions. Then we showed the full MELTS calculations from the Ghiorso thermodynamic model that at this point I had modified to the point where it could do this constant entropy calculation. It was the only model that could do the constant entropy calculation; all the other models were formulated in terms of temperature. That entropy formulation allows you to see freezing at these transitions. And so, we published this paper. The best ideas are ideas where people who understand the state of the field can read the paper and say, "Of course. Why didn't I think of that?" So, nobody ever said to me, "This paper's wrong." Because we explained it clearly enough that we had found the essence of why it had to be right. And at my first American Geophysical Union meeting, I was introduced to Dean Presnall, when I had just published this paper saying his whole way of thinking about this problem was wrong.

ZIERLER: This could go one of two ways. [laughs]

ASIMOW: I was introduced to him by another petrologist, from UMass Amherst, named Tony Morse, who is quite a character, and Tony pulled over Dean Presnall, and said, "Dean, this is Paul Asimow. This is Ed Stolper's student who caught you with your pants down."

ZIERLER: [laughs]

ASIMOW: [laughs] So, actually I had an ongoing debate with Presnall for several years.

ZIERLER: So, it wasn't settled as far as he was concerned.

ASIMOW: As far as he was concerned, it was not settled, that while my one-component system and my two-component system and the full multi-component MELTS model may have shown this one behavior, he was convinced that his five-component system, which was where he did his experiments, still showed the opposite behavior. And so, the sort of induction we were doing from one to two to ten components, skipping over five, he didn't accept that there weren't gremlins lurking in between.

ZIERLER: Has enough time passed where a verdict is in that's universally accepted?

ASIMOW: I don't know. I haven't talked to people about this issue in a long time. I've moved on to do other things. MELTS makes some real errors, some of which we fixed a few years later with a recalibration called pMELTS. It has the same behavior in this respect as MELTS but it's not quite as exaggerated. I would say it's not been that much attention focused on the spinel-plagioclase transition because, in fact, it's only really relevant in very cold parts of the mantle and not much of the mantle is that cold that most attention these days has focused on the somewhat higher pressure range where spinel peridotite is dominant anyway. And so, arguing a whole bunch over whether the spinel-plagioclase transition causes melting or freezing, not that many people are arguing about it because the spinel-plagioclase transition probably doesn't really happen, because too much melting has taken place by the time you get there—I would say is the short version of where that argument went. Before we run out of time, I want to tell one more story about being a student in this group encountering senior scientists and their interactions with each other. We had then, and we continue to have, a weekly reading group. It's now called Petrology Reading Group. At the time I think it was called SOS, Students of Stolper.

ZIERLER: [laughs]

ASIMOW: Where we pick often a fairly recent paper that has been published in the general field of petrology, we all read it, we get together, and we talk about it. One of the papers that we read when I was a student—this is maybe 1994—we had a visiting scientist that year. I don't know if it was the Fairchild Scholar or the Moore Scholars Program at that point—one of these senior visiting scientists named Albrecht Hofmann, who is—was—the director of the Max Planck Institute for Chemistry in Mainz, and a really important and influential geochemist. Really the most influential German geochemist. We read a paper—and Al was here for that reading—by Claude Allègre, the most influential French geochemist, which attempted to use principal component analysis to interpret the geochemistry of oceanic basalts, and it came up with a result that was really bizarre but in principal component space it seemed to be right. I didn't believe it, and I went home, and I got the original data before they got transformed by principal component transformation, which is a way of extracting the information from a complex multidimensional data set, and I saw why the data had been handled inappropriately and what was wrong with the treatment. Looking at the original data, it was obvious, and I came back the next week and I presented this to the group, and I said, "This is why this paper is total nonsense." So, Al, at the end of his visit to Caltech, went back to Europe, and he went and he told Claude Allègre, "Stolper has a student who says you're an idiot." [laughs]

ZIERLER: [laughs] All of these introductions you have to deal with.

ASIMOW: Then Al invited me, and actually also John Eiler who was then a postdoc here, to a meeting that the Max Planck Institute convened at their castle in Bavaria, this castle called Schloss Ringberg that was built by one of the mad dukes of Bavaria and then given to the city of Munich which didn't know what to do with it so they gave it to the Max Planck Institute which turned it into a conference center. This was the second Plume conference. The first Plume conference was here; it was convened by Don Anderson, who was advocating this unpopular position that mantle plumes underneath hot spots don't exist, got to get together a bunch of people to talk about plumes. A few years later, they had a second conference, and at this Plume 2 conference, I had the opportunity to sit down with Claude Allègre and explain what was wrong with this paper that he wrote. He was very stubborn, and it was a very long conversation, but after 90 minutes or so, he agreed that I had a point and said he would publish a retraction. Which he never did. [laughs]

ZIERLER: [laughs] It was a moral victory for you, at least.

ASIMOW: Yeah. But from the ability to see what was wrong with this paper and pick it apart, I impressed Al Hofmann, and I am guessing that years later when people had to write letters for me to be hired, or to be promoted, that probably Al was one of those letter writers. I don't know that for a fact; I'm just inferring that. In principle, the whole hiring and tenure process and who's writing letters and what the letters say ought to be very confidential, but somebody once let slip something like, "You have a few really big fans out there."

ZIERLER: "Oh, wow."

ASIMOW: So, now I'm just always trying to figure out who those fans were. [laughs] I think Al Hofmann was probably one of them, is probably one of them.

ZIERLER: Well, Paul, on that note, we'll pick up next time from this one paper, how you brought it in, and it's added to your thesis. Maybe we could just end editorially. I can harken back to what you said in our last session where, coming to Caltech, you knew that you would be treated like a colleague, not a student, and the story you told about working through this problem with Ed really and truly illustrates that. Not coequals, obviously, but you're working side by side. This is not a student-professor kind of relationship. This is two scientists working through a problem, obviously to great effect.

ASIMOW: Yes, exactly.

ZIERLER: We'll pick up for next time.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Monday, May 11, 2023. It is great to be back with Professor Paul Asimow. Paul, great to be with you again. Thank you so much.

Parsing Scientific Debates

ASIMOW: You're welcome. Thank you for coming.

ZIERLER: I want to clarify one point in this amazing story you shared with me where you found this fatal flaw in this paper by these eminent scientists. We didn't really get into how you characterized or how you thought about this disagreement. Clearly, the data told you what the data told you, but from their perspective, would you have considered this scientific debunking? Was this sloppy science on the part of senior people in the field—which is a phenomenon that can happen—or was there some legitimate scientific disagreement that might add an additional dimension to the fact that you were assured that there would be a retraction, but there never was? Among those options, or maybe you'd like to choose another, how do you think about what it was that you corrected?

ASIMOW: Just to be clear, last time I told two stories about meeting senior scientists that when I was a graduate student, I had found that there were issues with their work—the discovery that Dean Presnall's hypothesis for the origin of mid-ocean ridge basalts was thermodynamically weak is more important in the scheme of things, and we'll get to that. I think you were asking about this experience of reading a paper by Claude Allègre, the French geochemist.

ZIERLER: Yes.

ASIMOW: Noticing there was something funny about it and working it out and then having a chance, thanks to Al Hofmann, to go and explain it to Claude. It's an interesting problem. They used a statistical method of treating their data that can give a lot of insight, but in this case, it ended up concealing the real underlying structure of the data and producing a bogus result. The method is principal component analysis. When you have multidimensional data that you can't visualize, because to do so, truly, you'd have to see it in many more dimensions than we can see in, principal component analysis basically says, "What are the most important combinations of the dimensions along which the data has lots of variance? Let's just reduce the complexity of the data by projecting it into that reduced dimensionality space, and then you can visualize it." It can be very effective. In this case, what they were doing was taking concentrations of many trace elements. The periodic table is big, so there's lots of trace elements, and if you treat them all as independent dimensions, you can't really visualize everything. So, let's try to reduce the dimensionality to the point where we can isolate the variability among different kinds of basalts.

The additional wrinkle they put in, and this is the mistake they made, is that in many cases in geochemistry, the concentrations of trace elements are less informative than the ratios between trace elements because there are lots of processes that are not interesting to us that change the concentrations, but don't change the ratios. For example, if two elements very strongly partition into liquids during melting, and if you have some source in the mantle and you melt it by a very small extent, those elements will have a very high concentration in the liquid. If you melt it to a larger extent, their concentrations will go down by dilution. But maybe we don't care about the extent of melting; we just care about the properties of the source. And so, the concentrations are not informative because they also depend on the extent of melting. But if they're both very incompatible, if they both strongly prefer the liquid, then the ratio of those elements in the liquid just gets mapped straight from the source into the liquid, and it's almost independent of the extent of melting. So, better to look at the ratio because it tells you what you want.

The problem with this paper is they chose to form ratios of all these elements by dividing them all by thorium, which is at very, very low concentrations in mid-ocean ridge basalts. The result that they got then was very large ratios of all of these elements to thorium in mid-ocean ridge basalt, which made the mid-ocean ridge basalts look highly variable in their principal component space. Their principal component basically became dominated by pointing toward no thorium, towards division by zero, which is a very long vector because it goes to infinity. And so, when they took data, which are relatively smooth but near the origin in thorium concentration, and then basalt data for all these other islands which everybody thought were more variable than midocean ridges, which have lots of variability but at higher thorium concentrations, and when you only look at it as ratios to thorium, it makes these very, actually, scattered data look very smooth because you're dividing by a big number. Then, these very smooth data look very far from the origin because you're dividing by zero. And then they only looked at it in that projection space and they came up with this conclusion that was clearly insane but is what came out of their data treatment method.

The lesson that I took from this is, [laughs] if it's not there in the original data and you come up with some way of handling the data and revisualizing it and reprojecting it and you get an insane result, maybe the problem is in your way of handling the data and not in the data itself. So, that was that story. They didn't do anything wrong. They just processed their data in a way that might have created insight but ended up creating obscurity. Only by going back to the original data, before they had munged it, was I able to see what was going on.

ZIERLER: The broader question about scientific disagreement—how this struck you as insane, as you've called it, it was just totally off—obviously, you can't get in their head, but how might it be defensible that they looked at this data and clearly it did not look insane to them? Is it just simply that they were wrong? That was the nature of my question. Or is there some deeper scientific disagreement where you can see legitimacy on their side and there's an agreement to disagree? Or, no, they're just wrong; it's that easy?

ASIMOW: It was just wrong. It was a conclusion that was not supported by the data, that emerged from handling the data in a way that was inconsistent with the actual nature of the data and the uncertainties in the data. There is actually a mathematical error underlying what they did, which is that principal component analysis is a vector algebra operation and concentrations of trace elements act like vectors, but ratios do not. They do not have the mathematical properties of vectors. So, actually, yes, what they did was formally incorrect.

ZIERLER: And the breakdown is laziness? It's in the review process?

ASIMOW: Oh. [laughs] It's in not everyone understanding the mathematics at a deep level, both the people that were doing the work and presumably the reviewers, so that, yes, this made it to press even though it should not have. This is in my experience not that unusual. The peer review process is ineffective, or at least, incompletely effective at catching things that look good but are not.

ZIERLER: And nothing smacked of fudging or fraud?

ASIMOW: No. No, it was an honest attempt that didn't work out well. [laughs] But this is hopefully one of the things that we scientists all appreciate and that we teach our graduate students to appreciate. Just because something is peer reviewed and published does not mean it is right. The literature is full of junk, and it takes discretion and it takes time and it takes testing and replication, of course, to figure out how much of the literature is junk. Undergraduates generally don't appreciate this, and the general public doesn't appreciate this. It seems sort of like the secret knowledge that, at some point, during your scientific career, hopefully in graduate school, you come to appreciate that science is imperfect, and it is our role to work towards perfecting it, a goal we will never achieve, but you can't just take something as given because somebody published it.

ZIERLER: In your experience, how rare of an event is it where a graduate student discovers something so wrong by scientists so eminent and the reputational value that that confers? Have you witnessed this before? Have you heard stories from others? Or is this truly unique as far as you can tell?

ASIMOW: [laughs] Oh, it's not unique, no. I have no way to quantify how common it is.

ZIERLER: But it does happen.

ASIMOW: It happens, and it's one of the ways that you recognize that somebody is going to grow up to be influential, is that at least once that they strike gold. Just going about their business investigating and testing things, they discover there is something that needs to be fixed, there is a new way of thinking of this problem, and when you think of this problem in a new way you get to a different and better answer.

ZIERLER: To broaden the discussion out about this experience as it relates to the overall dissertation, if we were to imagine a puzzle, what piece would this be out of how many?

ASIMOW: That's not in my dissertation. That was just a throwaway.

ZIERLER: Oh, wow! [laughs]

ASIMOW: We read this paper. I saw there was an error in it. I came back to the reading group and said what the fix was and happened then to have the opportunity to present the fix to the original authors.

ZIERLER: And it didn't change the trajectory of what you were focused on otherwise?

ASIMOW: Right.

ZIERLER: Wow.

ASIMOW: It was ancillary geochemical learning. More fundamentally, the sort of main thread that led to my thesis started in a more formal reading group. We read these papers that were trying to parameterize polybaric basalt melting. We decided we should approach this problem thermodynamically. We brought in Marc Hirschmann and the MELTS code. I started hacking at the code. Once I got it to the point where I could run the thermodynamic path that we thought was relevant, I very quickly discovered that it behaves differently from our intuition. Where our intuition is coming from thinking about pressure and temperature as the independent variables the way people usually do, but during the mantle melting problem underneath mid-ocean ridges, pressure and temperature are not the independent variables. And we are not the first ones to say this. It actually goes back to the work of a petrologist at Berkeley in the 1950s named John Verhoogen. Verhoogen said, "This is a constant entropy process" and gained considerable insight from that, but the modeling tools that were available to Verhoogen in the fifties didn't let him work out all the implications of this idea.

ZIERLER: These were computational limitations?

ASIMOW: Data limitations as well as computational limitations. The idea of taking this thermodynamic framework for thinking about igneous processes that Verhoogen pointed the way towards was picked up by his colleague and coauthor at Berkeley about 20 years later, Ian Carmichael, who had this remarkable insight and then spate of productivity where he said, "We can do igneous petrology from a thermodynamic modeling perspective if we had these kinds of basic data. So, let's go and get them." He said, "Well, we need heat capacities of components and silicate liquid," and he got a student, Jonathan Stebbins, who within a few years was doing that better than anybody else. "And we need densities of components and silicate liquids." And he got a student, Rebecca Lange, who within years was doing that better than anybody else. "And we need compressibilities from ultrasonic velocities in silicate liquids." And he got a student, Mark Rivers, who in a few years was doing that better than anyone else. "And we need a model into which to assimilate all of this data and make predictions." And he got a student, Mark Ghiorso, who within a few years was doing that better than anybody else. And it was just this burst of this Carmichael group of putting together all of the pieces of quality data and understanding that by the 1980s and the 1990s led to this thermodynamic model that I'm still using that Mark Ghiorso has rightfully gotten most of the credit for, but it's rooted in his PhD thesis with Carmichael and the modeling framework that they developed. So, Verhoogen I credit with the insight that you should think of mantle melting as an isentropic process.

ZIERLER: As opposed to what?

ASIMOW: Isothermal or isenthalpic. There was actually an argument in the seventies over whether enthalpy or entropy are the right quantity in which to do this problem, and most people came down on the side of entropy. There are still some who argue for enthalpy. The point is, while entropy is a really useful quantity, it's also a very tricky one. It's not very intuitive and we don't have an entropy dial we can set on an experimental apparatus to control the entropy during an experiment. We have a temperature dial we can set to control temperature during an experiment, but that's not how it works in nature. In nature, when you have no heat flow and the process is reversible, the second law of thermodynamics tells us that the entropy is constant. In that situation, where you're not in equilibrium with an external heat bath that regulates the temperature, the temperature will do whatever it wants. If it wants to heat up, it will heat up, and if it wants to cool down, it will cool down. If you impose a temperature, you are deciding how the system is going to behave, and you're controlling it artificially. But all our laboratory experiments are at controlled temperature. So, you develop this somewhat difficult discontinuity where you can't really do the right experiment in the laboratory to simulate the natural process. Instead, you have to use the experiments in the laboratory to calibrate the thermodynamic model, and then you can use the thermodynamic model to describe the natural process.

So, petrologists doing experiments, looking at the way rocks melt and drawing their results in pressure-temperature space, and then drawing a reasonable path through pressure-temperature space that the rocks might follow, come up with one way of predicting how and where the rocks are going to melt. Once we had in hand a thermodynamic model where we could instead follow a path through pressure-entropy space and let the temperature be controlled by the internal thermodynamics of the system, we found that it was different in a couple of very basic ways. Our initial reaction, because we'd read these papers that derived an understanding of what should happen from pressure-temperature space—our first reaction to the results of the model was that "This can't be right." That was Ed's reaction. So, I ran the model again. It definitely did what I saw it do the first time. Then, we had this really, as it turned out, critical session at Starbucks where, on the back of a napkin, Ed remembered what he had learned from Thompson about how pressure-entropy diagrams look in simple systems. We sketched it out and we saw that a simple system would behave just the way I was seeing the complex model behave.

So, we wrote a paper where we said, "Look, this is how it behaves in a one-component system in pressure-entropy space. You can draw the complete phase diagram. You can analyze it rigorously. You can understand everything that happens, and clearly, when you get to a solid-solid phase transition that consumes entropy, the entropy is no longer available to create melt, and you will freeze the system, not melt the system." Then, we were able to do it in a two-component system, which is one extra dimension on the diagram, so they're a little bit more complicated but you can still work it out in complete detail and show everything that happens, and the behavior is there in the two-component system. Then we see the same behavior in this complicated numerical model of the ten-component system, but now we believe it because we understand it in the simple system by analogy and we can explain it and it's a thermodynamically correct argument. That was a very good paper because everybody who took the time to read it saw the problem in a completely new way and had their eyes opened and understood that this is the right way to think about the problem and it leads to a different conclusion than the intuitive way to think about the problem, once you recalibrate your intuition.

That was the essence of everything that developed into my thesis over five chapters of, "If we model this process thermodynamically, with both the complex model that is calibrated to try to do the full problem, but also looking back to simple systems whenever possible to see if the key behaviors are there, where we can really understand them and explain them completely, then we can gain some insight. My thesis—I don't remember exactly how many chapters, but the first chapter was this first look at what happens when you are conserving entropy and you hit a reaction in the solid phase assemblages and the fact that it's the opposite of what people have thought. The second chapter was originally a talk that I prepared Ed to give at the Royal Society of London that analyzed the question of, "When you're decompressing a parcel of mantle underneath a volcano and it's following a constant entropy path and it starts melting, how quickly will it melt, and how much melt will it produce over a given decompression interval?" This is another thing that everybody thought they knew, but they had been trying to implement this sort of thermodynamic approach but in very approximate ways that led everybody to consider that the rate of melting should be constant (in some models) or that the rate of melting should be very fast initially and then slow down (in some other models). They're both wrong; it should be very slow initially and speed up. And we spent a whole paper explaining all the reasons why.

ZIERLER: So, this upended theory.

ASIMOW: Yes. There were no experiments because it's not a process that you can simulate experimentally. So, there was a theory. There were simplified versions of the theory. There were attempts at a more complicated version of the theory that treated the experimental data wrong, or again, made mathematical errors. This is when I first encountered another very senior scientist who did a lot of important work that I kept butting heads against. His name is Dan McKenzie. He's been a professor at Cambridge for his whole career. He did a lot of the really important early work in the theory of plate tectonics as a geophysicist, and then he started moving into geochemistry, which can be a dangerous thing for geophysicists to do.

ZIERLER: [laughs]

ASIMOW: He wrote a series of very influential papers in the 1980s where first he worked out the first version of the theory of extraction of partial melt, of melt from partially molten rocks. Dave Stevenson also looked at that problem. They had slightly differing approaches in the eighties. That was the first experimental project that I was working on in graduate school, was kind of following up on McKenzie's way of thinking about that problem and doing the experiments to calibrate the parameters. But then McKenzie also developed a theory for adiabatic or isentropic decompression melting, and he wrote his equation for deriving the melting rate in a way that, in this paper we published in 1997, we realized was mathematically incorrect. The multivariable calculus was attractive but wrong.

Basically, if you have a function of many variables, you can write the total derivative—the rate of change of that function—as a sum over the partial derivatives of that function with respect to all of these independent variables and the derivatives of those independent variables. And that is true, but the variables have to be independent. McKenzie wrote the change in the entropy as a function of changes in pressure, temperature, and melt fraction. The problem is that the melt fraction is a function of pressure and temperature, and so that statement was wrong, and wrong in a fairly subtle way. And it took me until 2018 to explain this to McKenzie—get him to sit down and listen and understand what we were saying about his math.

ZIERLER: But you got him there eventually?

ASIMOW: I did, yeah.

ZIERLER: Wow.

ASIMOW: But also, because he's a good mathematician and a good physicist but not necessarily a good geochemist, the way he parameterized the data seemed to fit the data, but it missed an essential property of the data. If you plot from the beginning of melting, what we call the solidus, the minimum temperature at any pressure where a melt first appears, up to the end of melting, the liquidus, where the last solid disappears—many materials, the solidus and the liquidus are the same. If I heat up ice at zero degrees C, it will melt and it will melt completely to liquid at zero degrees C. Rocks don't do that because they're multicomponent, multiphase systems. They have a range of melting points at any given pressure between the solidus and the liquidus.

If you make a graph of experimental data, ranging from all solid at the temperature where melting begins, to all liquid at the temperature where melting ends, there's some continuous curve that connects them, going from (0, 0) to (1, 1). McKenzie looked at the available experimental data, which were mostly at pretty high melt fraction—there weren't any experiments in the eighties that got all the way down close to (0, 0)—and he said, "Well, this kind of looks like a cubic curve. It's concave down and then it's concave up, so I'll fit a cubic curve to it." Then he went and used that cubic curve, and the property of that cubic curve is that it was very steep near the origin. The actual behavior is that at about point (0.2, 0.2) on this plot that goes from (0, 0) to (1, 1), there is a kink in the curve. It is not smooth and differentiable. It rises to a kink, concave up, and then another segment concave up, and together, if you smooth through them, they look concave down, but only if you don't have the kink. So, if you fit a cubic polynomial, which is smooth, you get one functional form that goes through the data with some error, but if you know that there's supposed to be a kink there and you fit it with this other functional form, you would get a very different behavior right down near the origin where there wasn't any data. The fact that there should be a kink comes from insight that petrologists have about the way melting works that a geophysicist coming to the problem and just looking at the data and drawing curves through it wouldn't necessarily have.

The sort of mathematical disagreement about the right way to write down this calculus was one thing, but more than that, the thermodynamic model that we ran predicted a different behavior for this function of melting rate near the solidus, and we spent a lot of time convincing ourselves that actually this was right, and this was the way it should behave. The experiments have been very stubborn, even now 40 years later—or something—30 years later. The experiments have been very stubborn about confirming this behavior that our thermodynamic model says should be there, partly because the first version of the thermodynamic model exaggerated this effect due to some errors in the model or incomplete data sets in the model. The model was revised after my thesis around 2002, and it made this behavior a little bit more moderate, but still the same general effect is still there. So, there was the chapter on the solid state phase transition, and there was the chapter on the analysis of the melting rate. There was the chapter on testing some other assumptions or properties of McKenzie's models about the way that melts migrate.

Then there was the chapter where I tried to put it all together and run a complete model of, "If this is the mantle source composition and it upwells under ocean ridges, this is how much melt it will make and what composition of melt it will make. Then if it gets to the crust and fractionates, this is how it will evolve and what rocks you will make and what you can predict when you go out and pick it up on the sea floor." Put that all together into one big model. There's a version of it in my thesis in 1997, but the paper actually came out in 2001. This is what postdocs are for, generally, actually cleaning up the things in your thesis and getting them ready for publication. I did some of that to get it all ready. That paper ended up being published as part four in a series where Hirschmann was the first author on the first three parts, finishing this goal that we laid out, when Hirschmann came for his postdoc. "What does the MELTS model and this thermodynamic approach have to say about mantle melting?" turned out to be a lot more than one paper worth. This chapter four of my thesis ended up being one of that series of papers.

The body of work as whole was very original because it was the first application of this thermodynamic model that Mark Ghiorso and his mineralogy colleague Richard Sack built to do lots of things in igneous petrology, lots of things even that they didn't imagine that it could do, such that their interface for running the model didn't have all the capabilities we needed, which is why I needed the code so that I could get in and make the model do what I wanted it to do. It was really the first attempt to apply this model to this problem that is in some sense the most important problem in understanding igneous rocks on Earth because the whole sea floor is covered with mid-ocean basalt and that's 70% of the Earth's surface, and the Earth is always making this stuff and then recycling it back into the mantle and making more.

It was the first attempt to take this thermodynamic model and solve this problem, and it has on it the fingerprints of lots of important prior work that led up to this synthesis of what you could do with this model. Its intellectual parentage, I would say, goes back to Josiah Willard Gibbs and chemical thermodynamics, and to Norman Bowen and experimental petrology, and to John Verhoogen and this insight that this is an isentropic problem, and to Ian Carmichael and his mission to get the experimental data that you would need to actually implement this thermodynamic approach, and to Dan McKenzie who did a lot of the physical theory of what is going on with two-phase systems and migrating melts as well as the first attempt to really put together a quantitative model of how the mantle would melt and what compositions would come out. And Charlie Langmuir—we'll get to this—was one of my postdoc advisors, who in the 1980s with his student Emily Klein, compiled all of the chemical data from the mid-ocean ridge basalt classes and processed it in such a way that you could see through the noise and the secondary processes and develop a theory about what controls the variation among all the different segments of the mid-ocean ridge. Ultimately is what I was able to test with my model is, "Can I reproduce the correlations that Langmuir observed?" Mark Ghiorso and Richard Sack and their assembling this actual working model that took all of this thermodynamic data that allowed you to make predictions in a reasonable timescale. And Thompson and his way of thinking about phase diagrams, especially phase diagrams with non-traditional independent variables, like entropy. And Ed and his awareness of all of these things that were out there in the literature to point to me so that I could put them together. And Marc Hirschmann who was only a few years my senior but was very influential in helping me learn what this model could do and how to use it and collaborating on this whole project.

So, I had in my thesis presentation a slide that was titled something like, "The giants on whose shoulders I am standing," that had a pyramid of cartoonish, shirtless giants holding a big club with really big ones at the bottom and some standing on their shoulders and some standing on their shoulders and me standing on the top. But these are the scientists to whom I give credit for laying the intellectual foundation for me to put together this synthesis that I spat out into the world in my thesis.

ZIERLER: Besides Ed Stolper having the insight to put together all of these disparate pieces and focus your attention on it, how related was that to what he was doing and his own research at the time?

ASIMOW: Ed has very much worked for his career in a mode of bringing in excellent students or staff members and guiding them to master some area of science and produce interesting results. And so, his work for so long, since he was an assistant professor, has been so tied up with mentoring students and postdocs to do interesting things that it's actually hard for me to say what Ed is working on at any given time, rather than what Ed's group is working on. Not to take anything away from Ed; he is a master of all of these areas of petrology and meteoritics and geology.

ZIERLER: You're speaking to his devotion as a mentor.

ASIMOW: That, too. But when you ask, "How does this relate to Ed's work?"—it's actually hard for me to answer, because Ed's work is meteoritics in collaboration with his staff member John Beckett. And it's experimental petrology in collaboration with his staff member Mike Baker. And its infrared spectroscopy in the behavior of water and CO₂ in igneous rocks and melts in collaboration with a series of students and his longtime staff member Sally Newman. And it's thermodynamic calculations with his postdoc Marc Hirschmann, and his student, me. He doesn't write that many first author papers—quite few—because he works really well at identifying talent and mentoring talent and creating things in collaboration with junior scientists.

ZIERLER: Those are skills that make for a great administrator as well. [laughs]

ASIMOW: Yes, right. And you can only do so much yourself. This is why our model [laughs] of doing science in academic institutions is pretty successful. It's a force multiplier that allows—someone with ideas and the ability to inspire others to follow up on those ideas can end up producing a lot of science that they would not be able to produce working in isolation. So, yes, I have great admiration for Ed and his knowledge of many areas of science and especially for his ability to inspire and mentor young scientists, which is why there are so many students and postdocs of Stolper out there, running their own research groups now and carrying on his influence.

ZIERLER: Who else was on your committee?

ASIMOW: Dave Stevenson, who was there from the beginning because I started working on this experiment. Peter Wyllie, whose name has not come up yet, but Peter is an experimental petrologist who did a lot of important early work on melting of volatile-rich rocks—CO₂-bearing rocks and water-bearing rocks. He, himself, had one of these moments where early in his career he proved something that Norman Bowen, kind of the father of igneous petrology, something Bowen had said was wrong. So, he burst onto the scene in a big way with one of these disproofs of a dogma back in the early 1960s. So, Peter came here. He was hired from the outside to be chairman in this division. We've only done that once. Every other chairman has been hired from the inside, but after the Wasserburg chairmanship fell apart in disarray they brought somebody in. So, Peter Wyllie came from Penn State bringing his experimental apparatus with him and setting up a lab on the third floor of Arms. When I arrived on the faculty in 1999, Peter handed me the keys to the lab and said, "I don't want to have anything to do with it anymore." [laughs]

ZIERLER: [laughs]

ASIMOW: Peter was on my committee. He was a very big fan of our work and our new ways of looking at these problems, and I learned a lot of phase diagrams and experimental methods from Peter, but he wasn't really at the heart of what we were doing in terms of bringing this thermodynamic reasoning. That wasn't Peter's specialty. But just yesterday a graduate student had just turned in their thesis—she was just saying, "I turned in my thesis", and so this had me remembering when I turned in my thesis. In those days, you got it printed and bound and you handed a hunk of paper to the members of your committee two weeks before your exam. Of course, that's not how it works anymore. Now you get a PDF. But I got my thesis printed and bound—I'm looking for my thesis as opposed to all these other theses. I should have a copy of it somewhere on my shelf, you would think. Anyway, you can see a range on my shelf of what PhD theses look like. So, I handed it to Peter, and he said, "Oh, it's a nice thin one."

ZIERLER: [laughs]

ASIMOW: And then he opened it up and he said, "Ugh. It's double-sided." [laughs]

ZIERLER: [laughs]

ASIMOW: Peter retired in about 1999, about when I started and then took over his lab. He's still alive. He's still a professor, Emeritus. He's not been coming in very much lately, I think. His mind has been slipping of late, but in his retirement, he had ambitions to write books and keep learning and try to appreciate the new ways of thinking about these problems. He came and he sat through my freshman class just to see how I was teaching it.

ZIERLER: And very little or no interaction with Tom Ahrens as a graduate student?

ASIMOW: That's right. Not on my committee, not involved in the work that I was doing. He was in geophysics and planetary science, and this is a geology thesis with geochemical implications. I'm actually trying to remember who else was on my committee. There should have been a fourth member.

ZIERLER: Anything interesting from the oral defense that might spark that memory?

ASIMOW: [laughs]

ZIERLER: Any curveballs?

ASIMOW: No, defenses are misnamed these days. At least here. We are not a very adversarial community, and if the advisor has done their job and prepared their student, it is a discussion. Because the student should be the expert on the subject, not just amongst the committee but in the world—and I find this is generally true—the thesis defense is essentially a presentation and not so much a defense unless something has gone quite wrong. Ah, the other member of the committee was Mike Gurnis.

ZIERLER: Oh, wow, okay.

ASIMOW: With whom I still collaborate.

ZIERLER: He must have just arrived at that point.

ASIMOW: I think he'd been here a few years. I don't know exactly when he came from Michigan. Well, that's interesting—

ZIERLER: Was that from the computational angle to have Mike on the committee?

ASIMOW: Yes. Yeah, I think that made sense. Okay, and the chair of my committee who was my academic advisor was Geoff Blake, who also was kind of randomly assigned to be my academic advisor when I was thought of as a geochemistry student and somehow remained my academic advisor when I decided to be a geology student even though he's not in the geology option. [laughs]

ZIERLER: And is that SOP for that not to have been Ed?

ASIMOW: Yes, absolutely. This is key. In our division, every student has an academic advisor who is not the thesis advisor, and the committee chair is the academic advisor.

ZIERLER: This is to prevent blind spots, essentially?

ASIMOW: Yeah. This is so there's somebody else paying attention who can manage conflict that arises between a student and a thesis advisor, and then at the thesis defense, it is to avoid the person chairing the committee being too close to the work. So, yeah, actually my committee was Blake, Stolper, Wyllie, Gurnis. Interesting. I did not collaborate with Gurnis during graduate school, but years later after I joined the faculty, we advised a student on a joint project trying to combine thermodynamics and geodynamics—a student named Laura Hebert. And we are currently jointly advising a postdoc, again trying to do this same idea of combining thermodynamic calculation and geodynamic calculation. The geodynamics tells you how things move around, and the thermodynamics tells you what happens as they move around, and hopefully you can run a model that is not so computationally intensive that it doesn't go anywhere.

ZIERLER: At any point in your graduate career, in the later years especially, was there any noise about you returning as a faculty member? Did anybody intimate anything to that effect?

ASIMOW: No, not that I can recall.

ZIERLER: That would not have influenced where you wanted to go for your postdoc having an idea that you'd come back.

ASIMOW: Right. No, I think that they held their cards pretty close to their chests until they were able to get an offer through, and it must have been a difficult process because there wasn't really a search going on, as such, and we don't like to hire our own students. It's frowned upon. I never applied or gave a job talk other than my thesis defense. The faculty must have just sat down and said, "This is one of the most exceptional students we've seen. We need him back, and yeah, he does work that's similar to what Ed does, but he'll do something different, and let's just bring him in." What we could call a target of opportunity hire—when you see somebody extraordinary, the culture at Caltech is, "Forget your strategic plan. Forget whether the provost said you have a search open. Just get this person." Every now and then we do that.

ZIERLER: So, there was no open line for you. They really made one.

ASIMOW: Yeah. At the same time, my hire made sense in the context of what was going on during Stolper's chairmanship, which was a complete overturn of the geochemistry faculty. Bob Sharp hired a geochemistry faculty in the 1950s. By the 1990s they all retired, and it was time for a big burst of new hiring, and I ended up being part of that burst. So, we try not to draw a direct line, like, "This person retired, we need someone in their field," but Sam Epstein and Hugh Taylor and Gerry Wasserburg and Lee Silver and Peter Wyllie all retired. And John Eiler and I and Jess Adkins and Dianne Newman and a bunch of new geochemists were hired kind of in a cluster or a big burst. That was one of the repopulation things that Ed did while he was chairman. The other was to create the geobiology option and set it off, which involved both young hires, like Dianne Newman and Victoria Orphan and, eventually, Jared Leadbetter, and Alex Sessions, but also something we do pretty rarely, which is a senior hire, which was John Grotzinger across from MIT. So, yes, when I was finishing up and looking at postdocs, no, I don't think I had an idea that a movement was afoot to get me back. So, shall we move on to the postdoc search process?

ZIERLER: Yeah. What mentor advice did you get about best postdocs for you, if any?

ASIMOW: I don't know if this was mentor advice or I figured it out for myself, but there's kind of two different sorts of postdocs. There are soft money postdocs. Somebody writes a research grant. They include in their research grant salary for a postdoc, and then they go and try to find a postdoc to do the thing that they said they would do in the grant. And then there are fellowships, or hard money postdocs. There are institutions that have enough endowment sitting around that they can, every year, hire a postdoc, and they're hiring the person to do whatever that person does best, rather than matching a person to a project that has been funded. Hard money postdocs are better.

ZIERLER: Particularly if you have ambitions to improve the thesis research.

ASIMOW: If you know what you want to do. This is the problem with postdocs. Postdocs spend half their time publishing their thesis and half their time looking for a job.

ZIERLER: Yeah.

ASIMOW: [laughs] You would like them to do something else in between. Not all postdocs do. I don't necessarily love the idea of postdocs from the point of view of being a faculty member and mentoring them. They're a little hard to manage. But from the point of view of being a postdoc, yes, it's nice to have time to finish up the unfinished work from graduate school. It is nice to have the intellectual freedom to define what you think is important to work on next.

ZIERLER: That's only applicable in the hard money—

ASIMOW: Exactly. So long as the institution provides you the resources that you need—experimental, computation, whatever—to do the work, and that there are mentors there that are interested in what you're doing and qualified to contribute to it and help you continue to learn. You don't want to just go somewhere and get salary support to be completely alone and have to make up everything from scratch. That's not useful. The other thing about hard money postdocs is there's a calendar. [laughs] They post an ad. You apply. They make an offer. There's a cycle. It's more reliable, whereas soft money postdocs, whenever someone happens to have money, they might go looking for somebody, and they're harder to find, and they're less reliable.

ZIERLER: What about on the personal side? You're a family man at this point. What are the considerations there? Is there a two-body problem?

ASIMOW: No, because I got married in 1993, in my third year of graduate school. We had a son in 1996 in my fifth year of graduate school. My first wife, Jenny Factor, is a poet and had also trained as a Montessori teacher and was not really tied down to any particular place or job or time and didn't especially want to come back to California after college but did because I was here and then was happy to leave. So, no, I didn't feel especially constrained by moving with Jenny and Lev at that time. Maybe I should have been, but—so, I applied for the Miller Fellowship at Berkeley which is a three-year hard money position. I was nominated for the Junior Fellowship in the Society of Fellows at Harvard, which is sort of a postdoc. It's not exactly comparable to other things.

ZIERLER: The Miller Fellowship is associated with what school at Berkeley? That's bigger than geology.

ASIMOW: Oh, yeah. That's campus wide. It's a big program. I applied for the Carnegie postdoc at what's now Carnegie Science, but was then the Geophysical Lab, or Department of Terrestrial Magnetism, or both. That's in D.C. And I applied for the Lamont Fellowship at Lamont-Doherty Earth Observatory of Columbia. I did not get an offer from Harvard for the Junior Fellowship, and I did not get a Miller Fellowship. I don't remember whether I got an offer from Carnegie but given the directions that I wanted to go in, Lamont made the most sense. At that time, I was doing computations. I hadn't really gotten my hands on any real rocks to measure myself and work out what they meant and test my models against them, and I had moved away from experiments a bit. And so, with a fellowship at Lamont, I could work with Charlie Langmuir, who is an ocean-going petrologist. He goes out and he dredges rocks off the sea floor, and he brings them home and he analyzes them, and I wanted to learn to do that. And Dave Walker, who's an experimental petrologist, and who had been influential a generation earlier in Ed's early career—I wanted to learn experimental methods from Walker.

ZIERLER: Had you known either of them, or just by reputation?

ASIMOW: Just by reputation. Also there was a young computational geodynamicist who had been a student of McKenzie, Marc Spiegelman, and I wanted to continue—or at that point make a first attempt—to do the kinds of things I later did with Gurnis, of integrating thermodynamic calculations with fluid dynamic calculations. I wanted to work with all three of them, and with the Lamont Fellowship, I could do that. The postdoc was a really good time scientifically. I got my thesis papers out without it consuming all of my time. After six months that I'd been there, I got an offer to come back to Caltech. I said, "Great. Hold that for 18 months. I'm going to finish my two-year postdoc here." Caltech is very patient about giving junior faculty hires time to finish their postdoc and get some work done before we drop teaching and committee work and all this stuff on them. So, having my thesis out of the way, knowing what I was going to do next, then a postdoc is just two years to do your own work. And it's fantastic.

Postdoctoral Focus on Thermodynamic Modeling

ZIERLER: What were the loose ends in the thesis? What did you feel like you needed to clean up?

ASIMOW: There were two chapters that were not yet published that ended up being three papers that came out in 1999, 2000, and 2001, or something like that. I graduated in 1997, so it took a while to get those out the door. They needed polishing. Writing a paper with Ed can be a slow and iterative process. He reads very closely and very carefully and doesn't let anything past, so you really have to cross every "t" and dot every "i" before you can publish a paper with Ed. I admire that greatly; I don't think I'm nearly as careful. But then I started several new things. I started doing multi-anvil experiments, which is why when I started here, I built a multi-anvil device.

Charlie handed me a data set of rocks that they had picked up at that point, seven or eight years earlier on a cruise to the mid-Atlantic ridge, and because one student left and one postdoc left, the data had never really been organized and nothing had been written about it. So, I started systematizing those data which happened to be from the segment of the mid-Atlantic ridge near the Azores archipelago, which is a geochemical anomaly that contributes a lot of extra water to the source. That is why I started working on generalizing my approach to mantle melting, which I'd previously not considered the influence of water, to consider the influence of water so that I could do something with these rocks from the Azores region. That led to, first of all, a Nature paper that Langmuir and I wrote on conceptually understanding the influence of mantle water on mid-ocean ridge melting. That brought together several new pieces that were sitting out there kind of waiting to be integrated. One was the thermodynamic modeling approach that I had developed and its generalization to account for the presence of water. The other was Langmuir's model of similar processes that could be tweaked to at least give comparable results to show that the two models agree. The other is George Rossman's work.

George Rossman, starting with his student Dave Bell, triggered a revolution in how we think about what water is doing in the Earth's mantle. We know that there are hydrous minerals. When you write out their formula, they have H₂O molecules in them, or they have hydroxyl groups in them. Then there's lots of minerals that are nominally anhydrous. You write out their formula; there's no hydrogen in the formula. What George showed is, all the anhydrous minerals have some water as a trace constituent, and he spent much of his career trying to quantify how much water there is. But the way water behaves, if it's present in the mantle as a trace constituent in all the minerals, it's fundamentally different from the way it behaves if it's a major constituent of a very minor hydrous mineral. So, if you have, say, 200 parts per million water, it's either 200 parts per million in all the minerals, or it's 5% of a mineral which is then a really, really small fraction of the rock. When it's 5% in a mineral that's a really small fraction of the rock, when you start melting it, that mineral melts and then it's gone, and now there's no more influence of water, whereas if it's distributed through all the minerals, it slowly leaks out and it affects the whole melting process.

I came up with a way to describe that behavior, influenced by George's insight of what the water is actually doing there. That led to this Nature paper which gives this very counterintuitive result that when you add water to the mantle melting system, it promotes melting, and so it increases the total amount of melt that you get, but extending this idea that I mentioned earlier that the onset of melting is very slow and it speeds up as you go, the water makes it even slower and it makes for this very large volume that melts just a little bit. And so, the average extent of melting, which controls the amount of trace elements in the oceanic crust, the average extent of melting goes down even though the total amount of melting goes up because you're melting a much larger volume of rock. And nobody understood that. That was the simple point that was worth saying in Nature. A Nature paper is a good calling card for a young scientist. I wish it weren't true that these couple of journals are so influential, but having that paper was a good thing.

ZIERLER: The idea there being that publishing in Nature transcends the specificity of your discipline, that there's something more important to convey.

ASIMOW: Yeah.

ZIERLER: Which was what? Why did it make the cut for Nature?

ASIMOW: Because it combined a couple of new ideas that were permeating the literature and showed what their implications were in ways that nobody had thought of yet. And still, if people write a paper that has something to do with water and mid-ocean ridges, that's the paper they cite—Asimow and Langmuir—just because it was simple and to the point and it explained what's going on.

ZIERLER: Did you end up working more closely with Langmuir than Walker, than you had originally anticipated?

ASIMOW: Yeah. Walker and I didn't publish anything. I learned to do experiments in his lab. I played bridge in his office a lot, but we didn't actually finish anything.

ZIERLER: Personality? Just science? What was it?

ASIMOW: What was most new and exciting and could be accomplished in a reasonable amount of time. So then, just as Charlie handed me this data set of mid-ocean ridge basalts that I used as an excuse to figure out how to deal with water in the mantle, he also handed me a data set on abyssal peridotites, which are the rocks that you find in a few places on the sea floor that are the residues that are left behind after the oceanic crust is pulled out. They're what we call depleted peridotites that are a complimentary way to study the melting process. Start with fertile mantle, it comes up under midocean ridges. We partially melt it. We extract basalt, and we leave some stuff behind, but the stuff that we leave behind, due to accidents of tectonics and major faults and fracture zones, occasionally gets exposed on the sea floor where you can pick it up, and they provide a very different way of looking at the melting process that's sensitive to the details of the melting in a different way and allows you to see things that you can't see from looking at the liquid. We have a simple understanding of why that should be true and why we should look at the abyssal peridotites to try to learn about the melting process.

The previous holder of the postdoc position that I was holding, Yaoling Niu, had started working on these peridotites and compiled all the data and had left, leaving this unfinished compilation. I started looking at it and I realized he had done all sorts of dodgy things with it, and it needed to be redone and reprocessed. I did that, and when I looked then at this data set compiled and with the holes filled in my way that I felt was more supportable, I noticed something very interesting, which is from a trace element perspective, these rocks look like residues of fractional melting. Meaning, as you're melting the rocks, the melt is being pulled out and it's pulling out the trace elements with it and decreasing their concentration very quickly. Everybody was saying—this was part of what McKenzie was responding to with all of his work on melt migration—was that it's a fractional melting process in the mantle and part of the evidence for that is the trace elements in the abyssal peridotites. But when you develop the ability to model the major elements, which is more difficult than modeling the trace elements—but this is one of the things my model could do—when you look at the composition of the abyssal peridotites, they do not look like residues of fractional melting. In fact, they look like residues of batch melting, where the liquids are continuing to equilibrate with the solids throughout the melting process. So, how can it be both? There was at that time no synthesis, no model that could explain all the evidence from these rocks.

So, I wrote a single-author paper while I was a postdoc, published in Earth and Planetary Science Letters, which is a good journal, widely read, titled, "A model that reconciles major- and trace-element data from abyssal peridotites". And basically, the trick is very simple. You do some fractional melting, and you do some batch melting. [laughs] And the trace elements are sensitive to the fractional part and the major elements are sensitive to the batch part. So, Charlie just sort of said, "Here, Yaoling left this thing behind. See what you can do with it." And I saw what I could do with it, and I wrote this paper, and Charlie didn't feel the need to put his fingerprints on it, and so it was my work. That was another successful paper and a good outcome of the postdoc time. The other thing that came out of that postdoc time is that Charlie came to appreciate my ability to systematize data sets, and so a few years later when he wrote a proposal for a research cruise to go out and pick up a bunch of rocks, he invited me to participate, like at the PI level, even though I'd never been to sea before.

ZIERLER: So, your whole time at Lamont you didn't go out to sea?

ASIMOW: Right, no, I didn't end up going to sea until the fall of 2004, five years after I came back here. I had a lot of conversations with Marc Spiegelman, the fluid dynamicist, but we never actually got anything going in terms of joint work.

ZIERLER: This would be obviously a bit far afield for you, but I'm very interested in how as an oceanographic institution Lamont was really at the leading edge of plate tectonics where Caltech really missed the boat on that one. [laughs] Did you get that sense coming from GPS? Did you get that appreciation in some way about why a place like Lamont would have been a leader in the plate tectonic revolution?

ASIMOW: Not that much. I mean, you pretty much said it, that the secrets of the world turn out to be revealed on the ocean floor, and if you're not in the habit of exploring the ocean floor, you would miss it. That just wasn't the kind of work that Caltech was doing, but that was the kind of work that Lamont was doing, and so they were learning a lot of things. But a lot of the fundamental information that is out there on the sea floor had already been mined and systematized. No, my experience with my postdoc was that compared to the Division of Geological and Planetary Sciences here, which is now about 40 faculty and when I was a graduate school student it was probably closer to 30—80-some graduate students and, in those day, 50-some and now maybe 100-some postdocs, and just a handful of undergrads—this is a size of community that, at least while I was in graduate school, I was able to pay attention to the whole thing and go to the planetary seminars and go to the geology seminars and go to the geophysics seminars and have a sense of all of Earth science, at least all the Earth science that was being done at Caltech. And then, I went as a postdoc to Lamont where there are hundreds and hundreds and hundreds of Earth scientists, and it's too much. So, I rarely left the geochemistry building except for a few excursions to the geophysics building to talk to Spiegelman. I didn't go to the oceanography building, and I didn't go to the atmospheric science building, and I didn't go to seminars in those areas of science. My focus ended up really narrowing due to the size of the institution and in some sense, to me, the unwieldiness of it.

ZIERLER: There's an irony there. The bigger the place, the narrower your focus.

ASIMOW: Yeah. So, it was a good time, and I really value the two years that I spent there, and I learned a lot, and I wrote a couple of papers that turned out to be really useful for my career, but they didn't make me an offer to stay. After your postdoc there, there's something called the Storke-Doherty Lectureship that you could move into, but I wasn't that interested. The other thing that happened while I was there is, just about the time that Caltech sent me an offer, Harvard was searching in petrology because, as they do, they'd repeatedly denied tenure to all the junior faculty in this area. I had been an undergrad there, and I knew the people there, and Rick O'Connell, who of course was a Caltech alum and had been the second reader on my bachelor's thesis, called me up and said, "Will you apply?" And I said, "No. [laughs] I have no interest in being a junior faculty member at Harvard. It's not a supportive and friendly place to go. I know that Caltech is a supportive and friendly place to go, and I would rather go there." So, I declined the opportunity to actually apply for the job, just because it didn't seem like it would be any fun.

ZIERLER: Did you spend time on Columbia's campus at all?

ASIMOW: Almost none.

ZIERLER: So it really is that removed?

ASIMOW: Yeah. The undergrads mostly live down in Morningside Heights. The graduate students typically go back and forth, many of them live downtown, take their classes downtown, commute to Lamont to do research. The postdocs and especially the researchers that are not also professors in the Department of Earth and Environmental Science, they live near Lamont and they have no particular reason to go to the city except to see a show. Some of them choose to live in the city just because that's the lifestyle they want. I was more interested in a sort of suburban existence at that point, with a young kid, and wanted parkland nearby. So, we lived in Palisades and rarely went to the city and almost never for work, just because—hey it's New York City—until the last six months that I was there. This is now Spring of 1999, when Jenny and I separated. Our approach to that was, we rented an apartment in Manhattan not far from Columbia, and Lev, our little toddler, lived in Palisades in the house and Jenny and I went back and forth.

ZIERLER: Creative solution.

ASIMOW: Rather than each of us having our own place and the kid going back and forth. So, the last six months, halftime I was living in an apartment near Columbia, but even so, I was then getting in the car and driving out to Palisades every day for work. I wasn't going out to the Columbia campus that much. If you're newly single, New York City is not a bad place to be.

ZIERLER: Sure. You said it was six months when Caltech reached out. So, six months seems like they were really holding back. They would have made the offer sooner, but it's almost like they needed to give you a little breathing room before they did.

ASIMOW: Or that's just how long it takes to get an idea, shop it around the faculty, get letters, get a package written, get it voted on by the faculty, get it voted on by the IACC, get it voted on by the trustees.

ZIERLER: And so this was just an offer. This was not an offer to apply.

ASIMOW: Right.

ZIERLER: And as you said, no job talk, nothing like that?

ASIMOW: Exactly. When my students and postdocs ask me for advice in how to apply for jobs—

ZIERLER: [laughs] "Get an offer."

ASIMOW: [laughs] I don't necessarily have all that much—

ZIERLER: Is your sense—was Ed driving that, or is it really a collective effort?

ASIMOW: I think Ed being chairman at the time and having been my advisor, must have done his best to drive from the backseat. I'm sure he wanted this to happen, but if he'd led it, it would seem inappropriate. So, I don't know exactly how he pulled it off or who was pushing for it or how it worked. Appropriately, these things have been, and remained, hidden from me. Obviously, he was supportive and wanted it to happen, but I suspect he made it happen by influencing others to bring it forward.

ZIERLER: I wonder also if there was any concern of how closely aligned your research was with Ed, where Ed's career was going, ultimately that he would become less involved in the research?

ASIMOW: Well, yeah, there was that. He was chairman and I don't think it was clear at that point that he was then going to be provost or acting president or anything, but while our fields are clearly related, and it's been lovely to have each other to talk to all these years, we have not collaborated that much. We've done different things. So, once I knew I was coming back, I started talking to Tom Ahrens, actually. Once Tom knew that I was coming back, he saw this long-term plan to get his lab to outlive him by inviting me to take it over. I built my own experimental lab and thought I would collaborate with Peter, but he really was done, and the work that I was doing with rocks that I had picked up while at Columbia, that didn't have anything to do with Ed. It was some years before we actually collaborated on anything. And so, it worked out fine. Yes, we're both here, but I am not, and I don't think anyone would say I have been, redundant.

ZIERLER: Looking back, what was the value in holding off, in following through with your postdoc, not taking the Caltech offer immediately?

ASIMOW: Several. One was finishing the things that I started as a postdoc and getting them published and having the time to dig in and really do a good job on that stuff. One was time to actually write some proposals so that when I arrived here, I wasn't just starting fresh with my startup money. I actually already had some proposals in the pipeline for collaborative work with Tom Ahrens and for things that I would do with the equipment that I was building with my startup money. It's just time to mature and get some work done and soak up a different set of colleagues and collaborators and a different culture. It's not good for someone to spend their whole career in one place. And I'm pretty close to that, but no, I really appreciated having that time to work and breathe and do research and grow and just be somewhere else.

Returning to Caltech With a Rich Research Agenda

ZIERLER: Last question for today, and it flows from the previous question: how did that extended time at Lamont inform the kind of professor you wanted to be in your return to Caltech, the lab that you wanted to build, the experiments you wanted to pursue, your persona in the field, all of the above?

ASIMOW: The equipment that I added to Peter Wyllie's lab is the design of multi-anvil device that Dave Walker invented and that Dave Walker's former machinist who went into business built for me. So, certainly what I brought with me in terms of experimental technique, I specifically learned there at Columbia from Dave Walker. The really systematic process of curating a collection of rocks and getting the most information out of it and the idea of trying to measure everything you can measure on the same sample so that your data are multidimensional and rich, I learned that from Charlie Langmuir. What was practical and what was not practical in merging thermodynamic and geodynamic calculation, I made a lot of progress in understanding that through conversations with Marc Spiegelman—although we didn't actually do it; I ended up doing it some years later here, with Gurnis. But I think those conversations were important in setting the groundwork for that.

At the time I was there, Langmuir was very busy founding a journal, which I'm actually now one of the editors of—Geochemistry, Geophysics, Geosystems—we just called it G-cubed. Getting divorced. Having lots of projects going on. And he was not all that accessible to his students and postdocs. It was hard to get a meeting with him. You could turn in a manuscript to him, and it would sit for a long time, and I definitely saw that as a counterexample of how I wanted to be a group leader and mentor. 25 years later, I find myself with a lot of the same behaviors and pathologies of being over-committed and having too much going on, and not actually being able to turn around a manuscript when somebody gives it to me. But certainly, I had the ambition to be much more available and responsive and quick about things for at least as long as I could get away with it. And I guess I also, because I had the freedom as a postdoc to do everything, to do experiments and calculations and analyze real rocks and move all those things along, I learned that I liked working like that, and I was going to keep doing it. And so I have through my whole career refused to pigeonhole myself as an experimentalist or a computationalist or a field geologist. I will do all of those things because they are all useful and they are all fun.

ZIERLER: You knew coming back to Caltech, GPS would be a perfect place to do that? No surprise there?

ASIMOW: Yeah.

ZIERLER: We'll pick up next time when you return to Caltech.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Monday, May 15th, 2023. It is great to be back with Professor Paul Asimow. Paul, once again, thank you for having me.

ASIMOW: You're welcome. Good morning.

ZIERLER: We're going to reverse time a little bit. There's one topic we should cover before we get back into the chronological narrative—your musical career at Caltech, as a graduate student. We talked about your time at Harvard, all of your involvement in music there. When you came to Caltech as a graduate student, what musical opportunities were there for you to pursue?

ASIMOW: At that point, I had just come from really my whole social life and most of my spare time as an undergraduate being dedicated to the Harvard University Band, and I was entirely a band musician at heart at that point. So, when I learned there was a concert band, I went straight for that. At that point, I was a good flute player and piccolo player and a not-very-good tuba player.

ZIERLER: Tuba, if I recall, you picked up sort of on a lark, just to see if you could do it, when you were walking down to play? You weren't trained or anything like that.

ASIMOW: Right, never had a lesson, and the marching band needed tubas. I think I made the mistake of auditioning for Bill Bing first on tuba and tiring out my lip, and then on flute, and maybe not sounding as good as I might. I don't know.

ZIERLER: Who is Bill Bing?

ASIMOW: Ah, okay! Caltech has had a music program for a long time. It has varied in quality over the years and has bounced back and forth a couple times between the HHS Division and Student Affairs. But in the early 1970s, a trumpet player named Bill Bing was hired to direct the Concert Band and the Jazz Band, and did so for 40 years. His wife, Delores Bing, who was a cello player, also organized for those 40 years the Chamber Music program; may have founded the Chamber Music program as far as I know.

ZIERLER: Was the partnership with Occidental there at the beginning, or that came later, or even preceded them?

ASIMOW: I don't know how that began, or when it began. When I arrived in 1991, it was definitely the Caltech-Occidental Concert Band, a joint group, which was slightly awkward because Oxy is on semesters, and we're on quarters, and so the schedules don't quite match up. And, the commute can be a little bit of a barrier. But it was helpful to us to fill some seats in the Concert Band with Oxy students, and it was very helpful to them because there was a string orchestra there but no real performance opportunities for wind players.

ZIERLER: Would you play there, or they always came here?

ASIMOW: We would play there. This is an important angle, because Caltech does not have a decent concert ball.

ZIERLER: Beckman doesn't cut it?

ASIMOW: Beckman stinks. Beckman is a lecture hall. It is absolutely useless for music. The stage is not big enough for the full concert band. It used to be; the concert band was smaller and could fit on the stage. There's no green room space because the building is a circle, and so there's nowhere to put it. And, there's no way to extend the stage. First of all, public events won't give up any seats. Secondly, you can't light it or capture the sound in front of the curtain wall without building a truss, and that would wreck the architectural look of the interior. We've tried, and there is no way to rescue Beckman as a concert hall.

ZIERLER: How are the acoustics?

ASIMOW: Lousy.

ZIERLER: It's a lost cause, entirely?

ASIMOW: Right. You could digitize the acoustics. You can get an array of microphones and send it to a laptop and send it back out and just say, "Make it sound like the Concertgebouw," or "Make it sound like Symphony Hall," or, "Make it sound like Avery Fisher Hall." You can do that. But only if you can pick up the sound, and that requires the mics, and so—no, Beckman is no good. Ramo is okay, but it only seats 400, and it's nothing special. Thorne Hall at Occidental is spectacular.

ZIERLER: Ah!

ASIMOW: It is a great space, acoustically.

ZIERLER: Purpose-built?

ASIMOW: Yes. It has plenty of seating capacity, and plenty of room on the stage, and plenty of backstage space. The problem is, it's at Oxy, which is in the middle of nowhere. Nobody can find it. There's no parking. You have to walk up and down hills at night. So it has challenges, for an audience, but part of the collaboration between Caltech and Oxy was that one of our three concerts per year, we would perform in Thorne Hall and rehearse in Thorne Hall. And if we wanted to record, we would record in Thorne Hall. That was a valuable resource. Much later, that relationship fell apart for a number of reasons involving politics in the Oxy Music Department and their wish to stand on their own feet and have their own music program and not have their students come and participate in ours instead, which is too bad. But at that point, it was definitely a joint operation, which meant something on the order of ten Oxy students a year would be in the concert band.

The Bings were really central to keeping performing and visual arts going at Caltech all the way through the 1970s, 1980s, 1990s, aughts, and offering a really valuable extracurricular opportunity to generations of Caltech students, many of whom are very talented musicians. The size of the school is such that programs like music have this beautiful spirit of amateurism without lack of quality, and community involvement in that there is room in the Orchestra and in the Concert Band for not just the undergraduates, and not just the music majors, but all the undergrads that want to play, and the graduate students, and the postdocs, and the faculty, and the JPL community, and the alumni, and whoever. So it's a really interesting mixed group, and really a valuable getaway, I think, for a lot of the students. Bill was a good trumpet player, and an okay conductor, and just a really generous spirit, and ran a group that was fun to be in, that people wanted to be in.

ZIERLER: Are either of the Bings still with us, do you know?

ASIMOW: Oh, yes, absolutely. They retired about eight years ago now, but Glenn Price, the new director of what is now the Caltech Wind Orchestra—he didn't like the name "Concert Band"; it wasn't proper enough for him—Glenn hired Bill back as the brass coach. Within the structure of the Concert Band, there's a music director, and then there's a woodwind coach, a brass coach, and a percussion coach. Bill is still playing in the group, filling in third trumpet parts where needed, and coaching the brass section. Delores is not active on campus as far as I know, but she's around; she comes to shows. The Chamber Music program was taken over by its current director, Maia Jasper White, again about eight years ago. That's a very interesting endeavor, also. I never played with the Chamber Music group, but each quarter, they take all comers, and have to sort them into trios and quartets and quintets of matched ability, and find them literature that is suitable, challenging but not impossible. You start out with a bunch of notecards with, "Oh, I have 42 violins and 6 violas; what am I going to do?" [laughs] It's an interesting process. Anyway, it was obvious to me the day I arrived here for graduate school that I was going to play in this concert band, so I went and auditioned for Bill.

ZIERLER: Did you offer both piccolo, flute, and tuba?

ASIMOW: I did. And he made the sound choice at that time to put me on flute.

ZIERLER: Did you own a tuba? Did you schlep a tuba out here?

ASIMOW: I did not at that time own a tuba, because in the Harvard Band I had just been playing sousaphones that belonged to the Band, and here, the Band owns three concert tubas. Many years later, when I was on the faculty and one year there was an excess of flutes and a dearth of tubas—and at that point I had much more experience as a tuba player, and I had played in the Columbia Concert Band—Bill asked me to go and play tuba. I borrowed one of the Band's tubas, which needed some work, so I took it to Robb Stewart's brass shop in Arcadia, which is a really fantastic brass shop, and there, hanging on the wall, in perfect condition, was a Miraphone F tuba. I think Miraphone is the best brand of tubas in the world, and I always wanted to own one, if I was going to own a tuba. I never meant to buy an F tuba, which is a little kind of half-sized tuba, or rather two-thirds size, exactly. But, there it was, and the price was right, so I bought it. I learned to play a new set of fingerings, this small tuba, and that has been my main instrument ever since.

ZIERLER: Oh, wow.

ASIMOW: But, no, at that point, I did not own a tuba. I joined the Concert Band as a flute player. At that point we rehearsed in the basement of Beckman Auditorium, which is not a terribly big room and not great acoustics, but it was available to us year-round. I made Bill aware of the fact that I knew how to conduct at least a marching band, and so, the first quarter I was here, as we were preparing that fall concert, we were rehearsing a silly little piece called "The Whistler And His Dog," a novelty piece by Arthur Pryor. It had what musicians call a very complicated road map. Like in order to fit the whole piece on one small piece of paper, there are lots of repeats and signs and codas and you have to jump from here to there, and there to here. Bill couldn't figure it out—where we were supposed to go next—and so I raised my hand and said, "Oh, you're supposed to go here, here, here, here." He just handed me the stick and said, "You do it."

ZIERLER: [laughs]

ASIMOW: [laughs] And so, I conducted that piece on my first concert here, in the Fall of 1991. Then Bill gave me this incredible opportunity, three times a year for six years, to lead whatever piece I wanted with the Concert Band, and so I became the regular standing associate conductor as well as playing in the group. That's a really rare opportunity for an amateur, to have a group of musicians that are willing to sit there and watch you wave your arms at them. It's one of the things that I love about Caltech is, had I gone anywhere else, any proper university that has got a music program and a surfeit of students that want to play in the top-level groups, I wouldn't have been able to conduct. I'm not that good, I'm not professional, I have no real qualifications. But I love it, and here there's room for that. That's true of theatre, and that's true of athletics, and it's true of performing and visual arts, and it's true of all these things on campus—that there is a lot of talent, maybe without formal qualifications, and things that people like to do but aren't going to make a career out of, and there's room for people to do them. It's one of my favorite things about Caltech. I've been very loyal to this group all along. By the time I was graduating, I think Bill gave me an opportunity to conduct a whole concert and also to do some arranging.

ZIERLER: I was going to ask, was that your entrée into musical composition, the conducting?

ASIMOW: No, I've never really been a composer.

ZIERLER: But you have done arrangements.

ASIMOW: I've done arrangements, but that's different. That's working with existing material and shaping it to fit the size and the ability of the group that you are playing with and trying to make it sound balanced. It's very different from composition, easier. I don't remember if we got into my grandmother and my family history in music—

ZIERLER: A little bit.

ASIMOW: —six sessions ago, but my grandmother was a Yiddish folk musician, and she left—or she sang all of these Yiddish songs and played them on the piano, and my uncle recorded them, recorded her playing them, and I've transcribed them and translated them as well as I can, and I have that.

ZIERLER: What was the original recording device? What did he use?

ASIMOW: It was a VHS camera.

ZIERLER: Oh, so it was more recent.

ASIMOW: This was in the late eighties or early nineties. And I made a start on composing a concert band piece based on the songs, and the themes from the songs that my grandmother used to sing, but it was wildly ambitious. I planned for it to be a quadruple fugue, which formally requires not only finding a way for each melody to simultaneously play contrapuntally in four different voices, but eventually for all of the melodies that you use to be played simultaneously and work together contrapuntally. It's the kind of thing that Bach would just improvise in front of the king of Prussia for fun, right, [laughs] but—so anyway, I didn't ever finish that. At one point, the software that I was using got obsoleted by a change in operating system. I think I have a hard copy of the start that I made on that piece, but I'm not—then I started having children and things, and getting busy at work, and haven't gotten around to finishing it. Someday, I will finish it, possibly by scaling back the mathematical sophistication of what I'm planning to do with it [laughs], and just write the music.

So, no, composition has never really been my thing, but I've done a lot of arranging. It's part of the responsibility of the student conductor of the Harvard Band to arrange music, so each week during football season, the drillmaster would say, "We're going to play this tune at the show next week. We don't have it. Make it." The conductor would have a few days to whip up something that might sound good. Again, I got ambitious, and somewhere around my fifth or sixth year of graduate school—I've always had a fondness for the music of Charles Ives, and I decided to do a setting of just the last movement of Ives' second symphony for concert band, and I did, and we recorded it, actually. Every now and then Bill would do a recording project and we'd put out a CD. So there is in fact a recording of the Caltech-Oxy Concert Band playing my arrangement of Ives'—the finale of "Ives' Second Symphony." It's a very difficult piece of music, a very difficult arrangement, but it was a good group; we pulled it off. Then, I graduated and went off to Columbia. I actually came back sometime during my postdoc to play in a concert for the 25th anniversary of Bill Bing being the Band director. Then I came back to join the faculty and of course immediately rejoined the Concert Band, again on flute or piccolo at that point.

ZIERLER: You've kept up with flute and piccolo over the years?

ASIMOW: I was, at that point, but then maybe my second or third year in the Band, I switched back to tuba, and I've pretty much stopped playing flute. Absolutely stopped playing piccolo because of my hearing. I have terrible hearing and playing piccolo does not help. It's really loud and it's really high and it's right here. That's probably what triggered my hearing loss originally, was playing piccolo, and then probably conducting the marching band without hearing protection. And, it runs in the family, to lose your hearing at some point. So, no, I don't play piccolo anymore. I can still play flute. I started it early enough, and trained it hard enough and practiced enough, that it's in muscle memory. I'm probably not as good as I once was, but I can pull the flute out of the case after a year and play it, and I know where all the notes are, and I can still hit the high notes, and it's fine. But no, I'm really pretty much exclusively a tuba player now. I kept playing in the group, as a faculty member, and it's good to have some faculty members in the group. One, it's kind of exciting for the students, to see professors in some setting other than lecture and lab.

Concert Band is an example of a good place for social interaction between students and faculty that may be a little easier than, you know, going to house dinners and having rolls thrown at you. Faculty have a certain amount of pull on campus, and so, as a member of the group, and then as a member of a kind of advisory committee that the vice president for Student Affairs put together under Professor Steve Frautschi to sort of watch over Performing and Visual Arts, and then as advisor to the committee that built the Hameetman Center on how to build a decent rehearsal space, with Steve and Mie Frautschi's money, then eventually as chair of the search committee for Bill Bing's replacement, I've been able to shepherd the music program in the way that a faculty member can, and a student really cannot. That has been, I think, a significant way that I have been able to contribute. But really it's just at a certain level for me, I want to play, and I want to have a place where I can play. As a tuba player, if you haven't got a band to play with, you haven't got anything. It's not like you're going to sit at home and play tuba solo. Although in 2020, I really missed the fact that there were no July 4th concerts. The San Marino Lacy Park thing didn't happen. It was the pandemic, so I couldn't play in the San Marino Community Band, and so on. So I just took an amp, and software that knows all the parts to all the Sousa marches, and you can turn them off one at a time, and my tuba, and I sat in my front yard and I played all the Sousa marches, for anyone who happened to walk by. [laughs]

ZIERLER: [laughs]

ASIMOW: So, occasionally I will play tuba without accompaniment! But, I kept playing in the group. I kept having the privilege, thanks to Bill, of conducting one piece per concert and choosing whatever I wanted to play. So I could embark on a three-year cycle of Franz von Suppé overtures if that's what I wanted to do. As I gained seniority with the group and kind of moved from the transient population of students that play for a few years and then leave, into the very long-term stable population of people, some of whom have been in the group for 40 years, I've made friends with a bunch of members, both the students that come and go and the long-term members. We've formed spinoff groups, so I also play in an eight-piece traditional jazz band with several members of the group.

ZIERLER: Tuba in a jazz band?

ASIMOW: Yeah, Dixieland band.

ZIERLER: Aha!

ASIMOW: Tuba is the traditional bass in that format.

ZIERLER: Right. I'm thinking like—what's it called—the Louisiana Restoration Hall?

ASIMOW: Yeah, Restoration Hall, New Orleans. Yeah, that's the style. That's really a lot of fun. Let me explain how that works. I'm not really a jazz guy. I played jazz flute in high school, but I was never really good at it, never really learned to improvise well, and then didn't play jazz at all for 20 years. The Dads' Band Plus One is the name of the group. All the tunes were arranged by Les Deutsch. If you haven't heard about Les Deutsch as a part of Caltech history, you should. You should interview him. He's class of 1974, I think, as an undergrad. He has three degrees in mathematics from Caltech, a master's and a PhD also. He has been the organist at every Caltech commencement since he was a sophomore. He has worked at JPL for 42 years and just retired, as the senior director of the Interplanetary Network Directorate, which is to say, he makes sure that JPL is in communication with all of its spacecraft all the time. I think it's accurate to say that he singlehandedly saved the Galileo mission by developing the error-correcting code that allowed it to downlink data without a high-gain antenna. But he's also an incredible natural musician, not only on organ but on everything else. He plays either piano or cornet in the Jazz Band. In the time I've been in the Concert Band, I've seen him play trumpet, and baritone horn, and clarinet, and saxophone, and piccolo, and tuba, and kind of everything except double-reeds, and piano whenever we need a pianist. And, he composes. The Band has recorded several of his pieces. Just this weekend, the Jazz Band played the piece that he wrote for his own retirement from JPL.

Les is a very good jazz musician, and is willing to facilitate making a jazz band sound like they are improvising by writing everything down for the musicians that don't know how to improvise. So, all the arrangements that The Dads' Band plays are written out by Les, although there's room for solos for the people that can improvise. When originally I started playing in that band, I just followed the chart. Over the years now, the last ten years or so that I've been in that group and also the last five years I've been playing in another jazz group—a banjo band that consists of approximately ten octogenarian banjo players and me on tuba [laughs] as the bass line—they play from the lead sheet, which is to say just the melody and the chords. There, I'm making up the bass line as I go along, and now I've been practicing doing that for five years, and then coming back to the Dads' Band, I'm now much more willing to get off the chart and make up what I think is a good bass line to go with the music. I have been able to do that because of Les and his ability to lead a band and help people become jazz players. He is a remarkable figure, not only because of his role as the organist at commencement, but also because of his role in the Jazz Band, in the Concert Band, in the musical life of the Institute, he's worth talking to.

ZIERLER: Okay!

ASIMOW: Eventually it came time for Bill and Delores to retire. We put together a big retirement concert for them. We actually rented Ambassador Auditorium, which is a fantastic space.

ZIERLER: Where is that?

ASIMOW: It's just on the other side of the 710 stub, between Orange Grove and the Freeway, at Green. It's on the campus of Ambassador College or the Worldwide Church of God. This basically religious organization—I'm not sure I want to call it a cult—had a very generous tithing policy that allowed them to acquire a bunch of land in Pasadena and build a college and build a truly first-class concert hall with like all the finest building materials, the best marbles and the best metals. It's beautiful. Then they changed their tithing policy and couldn't subsidize the operations of the concert hall, which was always a losing operation, and it's dark most of the time now. But it's still there, and it's really a nice auditorium. We played a concert there, the Jazz Band and the Wind Orchestra and the Chamber Music groups, for the Bings' retirement.

Then we were able to run a search for a new director. Also at that time, the Performing and Visual Arts group of lecturers—they're not tenure-track faculty, they're not in a division; they're part of Student Affairs—they didn't have any leadership. The role of being director of PVA was not desirable enough for any of them to want to do it. But the vice president for Student Affairs at the time, Joe Shepherd, authorized a search for a director of Performing and Visual Arts who would also be director of the Concert Band, so that it was a full-time job and not a temporary part-time lectureship, and we could look for somebody really good. We got a lot of applications, and one was just so far and away more qualified than anybody else, there was just no contest—this guy Glenn Price, whose previous job was director of Wind Studies at the Cincinnati College Conservatory of Music, which is a professional music school. Wanted to move to California, wanted to know people for more than the couple of years that master's students would spend cycling through the Conservatory, and applied for this job that seemed to me to be well below him. But the committee loved him. We brought him out to conduct the Band, as well as some other candidates, and they were like, "Well, obviously." So, he took the position, and he has taken the Band to a whole new level. He has changed it to the Wind Orchestra and he has taken it to a whole new level of professionalism and ambition of the programs that we play. Not necessarily more popular with audiences. Bill was very popular with audiences and ran a kind of mix of classical and pop music that really brought people in. But I think for the musicians, the Wind Orchestra under Glenn Price has been a more enriching and more educational experience. It was a very challenging transition for me, because I had been playing basically second tuba, because we had a ringer playing first tuba, a tuba student at the Colburn Music School downtown.

ZIERLER: What does "ringer" mean here?

ASIMOW: Professional. Like when you have an amateur group but you need to bring in some extra talent to make the group work, you hire a ringer. So, this basically tuba soloist, professional quality player, Gabriel Sears, was playing first tuba, so it didn't really matter that much what I played, because he was always right, and he was pretty loud. And, Bill Bing was not that demanding a conductor. Then Gabe applied for the conductor's job and did not get it, and so he left. He didn't want to play in the group anymore after not being hired to run it. So, suddenly I found myself playing first tuba with a conductor who hears everything, and knows [laughs] whether it's right or wrong!

ZIERLER: [laughs]

ASIMOW: That was a big step up for me in my playing, at that point.

ZIERLER: This was as a faculty member. This is more recent?

ASIMOW: Yeah, this is 2016. More recently, Allen Gross, the director of the Orchestra, which also used to be a Caltech-Oxy joint operation, and he was a tenured professor at Oxy and a lecturer here, he passed away, and we did a search for a new Orchestra director that was inconclusive. Didn't find anybody we really liked, and so Glenn said, "Well, I'll do it on an interim basis." Then the pandemic happened, and so four years later, Glenn is still the director of both the Concert Band and the Orchestra. He has a process in place to replace himself as Orchestra director, but it has not reached fruition yet.

ZIERLER: Has JPL—anybody who is interested there, do they come here, or do they have their own self-contained musical program?

ASIMOW: Nothing big. There may be small-scale groups that are organized around JPL, but they are welcome to play in the Orchestra and in the Concert Band and in the chamber music groups here on campus, and they often do. So, yes, a number of JPL people have been playing in the Wind Orchestra or the Orchestra for many years.

ZIERLER: Ballpark, how many committed faculty musicians are there at any given time?

ASIMOW: Two.

ZIERLER: Two. Who's the other?

ASIMOW: Right now, Austin Minnich, who is a Professor of Mechanical Engineering, who plays trombone in the Jazz Band. Oh—three. [laughs] The other is Julia Greer from Materials Science. But as a piano soloist, she's not going to spend a lot of time playing with groups. She may have done some chamber music with the students, but she's really a soloist. If the Orchestra is not willing to dedicate a concert to putting her upfront, she's like, "I'm not going to play."

ZIERLER: Historically, is that a small number now? Were there more faculty involved when you were a grad student?

ASIMOW: No, it's typical. Faculty are busy, there are many demands on their time, and only a few of them find room in their professional and personal lives to take advantage of what I think is this incredible resource, of being able to play music for life. This kind of music. So, yeah, there's usually a handful, but not much more than that. Niles Pierce played trumpet in both I think the Concert Band and the Jazz Band for a couple years when he was an assistant professor, and then he got busy. Warren Brown is very active and was in the Orchestra for many years as a French horn player. But it has never been a lot of people. I wanted to get all that on the record, because I really have treasured the ability, the opportunity, to play in this group, and the way that Bill Bing welcomed me into the group and gave me this opportunity not only to play but to conduct, and Glenn's tolerance [laughs] of my continuing [laughs] work with the group.

ZIERLER: Clearly it has enriched your Caltech life in ways that are immeasurable.

ASIMOW: Yes, absolutely.

ZIERLER: To close the loop, do you have insight onto the Oxy-Caltech breakup, how that came about?

ASIMOW: I didn't entirely understand it. The Oxy people felt very touchy about communicating with Glenn after being fairly comfortable communicating with Bill, and they really wanted to strike out on their own and have students focus on Oxy-centered activities. So there were just sort of a series of misunderstandings and miscommunications and political machinations at Oxy that eventually just led to a breakdown in the relationship and they said, "We're not going to participate anymore."

ZIERLER: Caltech has been basically okay since that? Has there been a loss from Caltech's perspective?

ASIMOW: No, because we can always fill seats with community people. If we don't have a bassoon player, we can find a bassoon player. No, the group is just as strong without the Oxy students as it was with them, except that we don't get to play in Thorne Hall anymore. But that means we don't have to drive over there anymore. With the construction of the Hameetman Center and the Frautschi Rehearsal Room, we solved the problem of having a place that is ours to practice that sounds good and that we don't have to clean up after every rehearsal and set up before every rehearsal. That's a big thing. When the Frautschi gift came in, and the Hameetman Center got off to a planning stage, I went to talk to the committee several times, and I said, "First, the acoustician; then the architect. [laughs] Don't do it the other way." There are so many lousy performance and rehearsal spaces where the acoustics were an afterthought. And they heard me, and that's a good space, and just because Glenn was busy doing something, I had the opportunity to conduct the first rehearsal in there, when it was built. That's a good thing; the rehearsal space problem is fixed. The performance space problem is not fixed, and this has been a long series of disappointments. There was a plan at one point to build a new 800-seat concert hall as part of a campus center back under President Baltimore.

ZIERLER: Where would that have gone?

ASIMOW: Maybe where Physical Plant is, kind of north of Browne Dining Hall, east of Jorgensen.

ZIERLER: Was Baltimore supportive of this?

ASIMOW: Yes, Baltimore was very interested in arts on campus. There was money, in the form of a gift from Ben Rosen, but after a fair amount of dithering and exchanges over what was the scope of the project, and what would be in it, and whether it was the best thing to do with the money, Stolper eventually redirected the Rosen gift to bioengineering. As often happens on campus, the demands of the science and technology and the divisions tend to come first, and Student Affairs and Performing and Visual Arts tend to be an afterthought. So, we almost got a concert hall, but didn't. It's still a challenge. There isn't really a proper theatre for TACIT to use that has backstage space and above-the-stage space for sets, so there's a limit to the ambition of the productions that they can put on. The Concert Band is really too big for Ramo; to have like a 100-piece concert band in a 400-seat hall is sort of unbalanced. [laughs] We ought to have a professional quality performance space on campus. We don't, and not clear that we ever will.

ZIERLER: The next campaign is coming up in a few years. Maybe something will get earmarked for that.

ASIMOW: Maybe. I doubt it. [laughs] It would be nice. There's also a long history of friction over the use of Ramo, between the HHS Division, which controls the building, and the Performing and Visual Arts, and public events offices, which use the auditorium. They just can't seem to get along, which is too bad. All right! I think that's it for music.

ZIERLER: Back to rocks?

Breadth and Depth for Junior Faculty Research

ASIMOW: Sure!

ZIERLER: [laughs] We left off last time—you were setting the stage for your research agenda, thinking about joining the faculty, what you would accomplish here. You emphasized your refusal, seemingly strategically, to be pigeonholed either into computation, lab experiments, or field geology. You wanted to do all of them. That raises the classic question that faces every junior faculty member: whether you are hyper-focused on the thing that you are best at and known at, because that's your ticket to tenure, or, you want to be broad and diverse and do lots of different things. Both models work at Caltech because of the amazing way that Caltech supports its junior faculty. But if you were self-conscious in not wanting to be pigeonholed, what concerns did you have about going for breadth over depth in those valuable pre-tenure years?

ASIMOW: I have seen this happen many times—that tracking committees at the midterm review of the junior faculty appointment always advise people to focus. Generally speaking, junior faculty ignore that advice and keep doing the things that they're doing, because they can see where they're going, and it usually works out well. I'm not sure anybody told me I should focus. I don't remember. But I've seen this advice given many times. The computational work was already off and running and mature and yielding results at a steady pace, and I knew it was good stuff, and I knew I was being recognized for it, and it was not hard to keep doing it. Experiments are challenging to get going. Especially if you're building anything new, that can take a lot of time before the equipment is working, you find a student that you can train to do it, you get some papers out, those papers get noticed. You really have to hit the ground running. I had the advantage of taking over a working lab and then inheriting another working lab, and so being able to get moving with experiments right out of the starting gate.

ZIERLER: Which of the two was Tom Ahrens'? Not the initial one; that came later?

ASIMOW: Initially I got Peter Wyllie's space, with working piston cylinder and gas pressure vessels, and I added the multi-anvil device. There was some spin-up time in getting the multi-anvil device installed and getting it working. I was able to hire a postdoc who evolved into a lab manager to get that thing running and keep it running. Tom Ahrens didn't retire until 2006, so there was a gradual transition where even before I arrived, I participated in one of Tom's proposals as a co-investigator. Then when I got here and had PI privileges, we wrote another set of proposals where I was co-principal investigator. Then a couple years later, it was time to renew some awards, and I stepped up to be principal investigator. Then by the time Tom retired, I was PI of all the awards. There was about a five- or six-year transition period there, as I became more and more involved in the Shock Wave Lab.

ZIERLER: A counterfactual question—the multi-anvil interests, would that have been part of your research had you not gone to Lamont, do you think, or was there something so fundamental about your time at Lamont that it steered you in that direction?

ASIMOW: The capability of the multi-anvil device is to do experimental petrology at higher pressure than the piston cylinder can reach. The thermodynamic models that I was using to model melting are basically calibrated on ambient pressure and gas pressure and piston cylinder experiments, and so there are very few experimental constraints beyond 2 GPa, maybe 3 GPa, where a GPa is 10,000 atmospheres. So, 3 GPa, 30,000 atmospheres, is a depth in the Earth of about 90 or 100 kilometers. Anything that happens below that, we can't model very well, in part because the functional forms that we're using don't extrapolate that well, and in part because we don't have much data to support the calibration. It was clear to me that if I wanted to be able to model melting at a higher pressure, which is what happens when the Earth is hotter, either at anomalously hot places like Hawaii or Iceland, or in the early Earth when the whole Earth was hotter, because it has been cooling over time, we would need to be able to model melting at higher pressure. And, if we need to model melting at higher pressure we need experimental constraints on melting at higher pressure.

The multi-anvil device was a logical place for me to move to, so that I could contribute data to the calibration of the models that I use. I felt—and actually now that you bring it up, I remember this feeling—that simply as a user of experimental data, I was a little bit of a parasite, like I wasn't contributing to the calibration database; I was simply exploiting the data that were there. I wanted to contribute, and also be able therefore to choose exactly how to do the experiments and what compositions to work on, and what pressure and temperature ranges to work on. So, yes, I wanted to build the database and not just use it, and one of the clear gaps in the database was that it fell off the deep end at high pressure. So, the multi-anvil device was a logical place to go. It's one of the reasons that I went to Columbia is we didn't have multi-anvil capability here and nobody here knew how to do it. I wanted to go learn how to do it so that I could eventually build that capacity in my own lab. Now it turns out that what Dave Walker is known for really is simplifying the multi-anvil device. When he started learning it, the traditional way, he thought it was really fussy and complicated and difficult and slow, and I think also he had personality conflicts with the person he learned it from at Stony Brook, a scientist named Tibor Gasparik. And so, he turned his brilliance to simplifying the construction of the device and the operation of the device, so you could do more experiments more quickly. I learned the method from him, the simplified quick and a little bit dirty method.

ZIERLER: What does "dirty" mean here?

ASIMOW: It's not as precise, and it doesn't go to as high a pressure as the original method.

ZIERLER: But it's a reasonable tradeoff given the other benefits.

ASIMOW: Yeah. A number of labs still use the Walker method, but once I had this lab and needed to operate it and had startup money, I hired a postdoc who had trained at the Bayreuth Geoinstitut in Germany in traditional multi-anvil technology, and he came here, and he's like, "I'm not doing that Walker stuff. That's junk. We're doing it right." Pretty quickly, I took my hands off the multi-anvil device and stopped doing the experiments myself and let Jed Mosenfelder, who came as a postdoc, stayed too long to still be a postdoc—and so I had money to hire him as scientific staff. I think he stayed with me 12 or 13 years before moving on to be lab manager at Marc Hirschmann's lab at University of Minnesota. By the way, this is something that I keep doing. I hire postdocs and then they don't leave.

ZIERLER: [laughs]

ASIMOW: They become valuable to the operation. I offer them a long-term career as a staff scientist. They don't necessarily have the ambition to be faculty members. And so, this works well for both of us. I think this has happened four times, that someone has come as a postdoc in my group and stayed for a significant fraction of their career. Two of them are still here: my programmer who does all the computational and software engineering, Paula Antoshechkina, came as a postdoc and never left; Oleg Fatyanov, who came as a postdoc to work with Tom Ahrens and me in the Shock Wave Lab stayed for 15 years before going back to Russia; and Jinping Hu, who is my staff scientist in the Shock Wave Lab now, came as a postdoc, transitioned to staff scientist. You can only be a postdoc for three years, so this is one of my ways of recruiting expertise and then getting long-term professional development to keep complicated experimental and computational jobs going, is promote—I don't know if it's a promotion or not, but postdocs to staff positions, which as long as you can keep raising the money, people can keep doing it forever.

Increasing Involvement in Computational Geology

ZIERLER: When you were thinking about continuing the computational work—right around this time I know, in the Seismo Lab for example, Mike Gurnis, Jeroen Tromp comes here, because there's now a new age of high-powered computation for geophysics. It's adjacent, but was that world part of what was exciting to you, the new capabilities of computers, and what they could do in geology generally?

ASIMOW: Yes. Just the increasing power of an individual workstation, where a laptop now is more powerful than a workstation was 20 years ago, has made the relatively small-scale calculations that underlie most of what I do much more efficient. A calculation that used to take 20 minutes now takes 10 seconds, and that's handy. Originally, actually, compiling the MELTS code on a SPARCstation 2 took like four hours, and now it takes five seconds or whatever. But I didn't have at that time very many really large-scale computing ambitions that would require an enormous cluster. We did, in collaboration with Gurnis, try to do something pretty expensive, which is do a geodynamic flow calculation, where you're following some large part of the mantle and moving material around, and at each grid point and at each time step, you're trying to use the thermodynamic code to calculate the physical state, whether it's molten, how molten is it, what are the densities of the phases. Something that is very desirable to do, but it's very difficult. Because when you're doing small-scale thermodynamic calculations, if the calculation fails now and then it's not a big deal; you go and you fiddle with it until you get an answer. But if you're doing millions of them, they have to all work, all the time, every time. So, most of that project was dedicated to finding fixes for the failures in the model. Also at that time the codes that we had, the thermodynamic code and the geodynamic code, didn't really talk to each other internally at code level. So one would write out files, the other one would read in the files; write out files, the other one would read in the files. That's slow and inefficient and limits your ability to parallelize the code and really take advantage of the big computer. So, we did some of that, and we had a student, Laura Hebert, who wrote a successful thesis doing that kind of work and went on to do a postdoc in that kind of work. But I wasn't really involved in designing the first generation of the large cluster that Tromp led the construction of. I was just a user once it was here.

ZIERLER: What kinds of things did you use it for? What was valuable to you?

ASIMOW: I used it for that attempt to merge geodynamics and thermodynamics in Laura Hebert's work. Then, over the last, I don't know, 15 years now, I've started dabbling in density functional theory and molecular dynamics, and expensive nanoscale calculations, as opposed to expensive geological scale calculations. Thanks to the Nobel Prize winning work of the computational chemists like Walter Kohn, we have density functional theory which is an almost—almost—exact recasting of the Schrodinger equation that is practically solvable for many electron problems, whereas from the pure physics point of view, it becomes very difficult to exactly solve the Schrodinger equation for a system that is of any interest much larger than a hydrogen atom. Computational chemists can do anything these days, with some approximations. But the more atoms you need in your calculation, the more expensive it gets, and if you're studying liquids, as I do, they're not periodic, so you can't just represent them with a small unit cell full of atoms and then fill space and say you've calculated everything. You have to have a lot of atoms, and their behavior is time-dependent at fairly long time scales. If you watch a solid for long enough for all the atoms to vibrate a couple of times, you've learned everything and you can just extrapolate that through all of time. But in a liquid, the atoms are wandering around and diffusing, and especially at low temperature, you may have to watch it for—milliseconds, seconds—hours [laughs]—to actually capture all the behavior. That makes liquids challenging for these methods, but liquids are what I'm interested in.

So, especially in collaboration with Bill Goddard from Chemistry, whose specialty really is not doing the quantum mechanics—using just enough quantum mechanical calculation to tune an empirical function that predicts the forces between the atoms, and then using that empirical function to do the molecular dynamics and follow lots of atoms for lots of time without having to do the quantum mechanical calculation all the time. That's how Bill has succeeded in all the things that he does. It's a natural way to study the problems that I want to study. Nevertheless, those calculations require a fair amount of computing power, and so, I have had several students who have focused on either density functional theory for solids or small liquid systems, or empirical molecular dynamics for larger liquid systems. That's a fair fraction of my activity these days, because there is a limit to what we can do with experiments. There are conditions that we cannot get to. There are things that we cannot measure. The computational chemistry, the atomic scale or quantum scale computational chemistry, lets us fill in the gaps or figure out what we don't know. It doesn't quite in my view stand on its own yet; we still need the experiments. The computational chemistry can't put the experiments out of business, because there are approximations in the computations. Some of those approximations are convergent. That is to say, the bigger your computer is and the more money you're willing to spend on computational cycles, the closer the calculations approach truth. But some of them are not convergent. It doesn't matter how big your computer is; the calculations are just wrong. Someday, somebody will figure out an exact solution to the electron exchange correlation potential, which is the missing piece of density functional theory, and then it might be true that the computations will put experiments out of business because you can compute anything exactly. We're not there yet.

ZIERLER: But it's still a simulation.

ASIMOW: It's still a simulation. It's called an ab initio simulation if you're doing the quantum mechanics, meaning it doesn't depend on experimental input; it predicts everything just from first principles. But it doesn't predict everything right because we don't have an exact solution to the equations. I recently had a student that worked with me and with Bill Goddard that—her work is a nice model for the way I approach these problems. She used a small set of ab initio molecular dynamics calculations, where you actually solve the density functional theory to get the atomic trajectories. Used those as a basis for tuning an empirical force field, so that we could do larger scale calculations with more atoms for more time and get better precision—less noise and less scatter in the simulations. We studied those results to find simple functional forms to which we could fit sparse and imprecise data from the shock wave experiments. We can only do so many experiments, and there are uncertainties in the experiments. If you try to fit them to very complicated functional forms with lots of parameters, you end up overfitting. You end up fitting the noise rather than the signal. Or, you just don't have enough constraints to fit the parameters at all. So we need simple functional forms that have very few parameters that we can constrain from the experimental database. We use the simulations, look at their systematics, try to abstract simplified but robust functional forms from them, and then we fit that to the experimental data, so at that point we essentially throw away the simulations. The fit to the data are no longer the same as the simulation because all the parameters are refit. But the functional forms we use were inspired by the internally consistent set of simulations.

I find this to be a constructive way forward to optimally use sparse experimental data to extrapolate to conditions where I don't have experiments, and to optimally use simulations that aren't right but they're nevertheless instructive and they're internally consistent in their own little world. Which kind of harkens back to what Ed and I were doing years ago, where we know MELTS isn't right, but it's thermodynamically rigorous, and the systematics are robust. So even if you're offset from experimental reality, you can still look at how things depend on each other, and gain insights, which you can then hopefully port to a model or an experimental database which is accurate, but understand what's going on in between the experimental points using the insights you gained from the theory. That's how I use a combination of experiments and theory to gradually make progress, gain insight into the relations and the underlying systematics, gain accurate constraints but sparsely distributed, and put them all together. That's one of the things I'm using big computers for these days, is quantum simulations.

Meanwhile, we are ready to have another go at large-scale combined geodynamic and thermodynamic calculations, because Paula, my programmer extraordinaire who has been with me now for almost 20 years, has created an interface where large-scale codes for geodynamical calculation, if they're written in Python or MATLAB, can directly access MELTS calculations without having to write out a bunch of files and read them back in, which is much more efficient in terms of time and memory allocation and can more gracefully handle failures. It's time to do that again. Gurnis and I have a postdoc now, Qian Yuan, who wants to do this kind of thing, and we've written a proposal to actually do it. This will be the first time in about 15 years that we have really taken on this kind of coupling to do a big joint problem. That will be a pretty expensive calculation, but the way parallel computing has evolved, we don't have the GPS cluster anymore; we merged it into the high-performance cluster at the center of campus. For this, it turns out to be better to run it on an NSF cluster where you don't have to pay for the computer time at all if you have NSF funding.

ZIERLER: One of the other big transitions when you joined the faculty is the internet and connectivity. How did that affect your research in terms of access to data, sharing data, not having to go to a library if you want to look something up?

ASIMOW: Hard to say, because I didn't do that much work in the pre-internet era. Certainly it enormously facilitates communication with coauthors and the building of collaborations, to not have to go see people in person.

ZIERLER: But there isn't a worldwide data network for you to tap into or contribute to, in your field?

ASIMOW: [laughs]

ZIERLER: That would be facilitated by the internet.

ASIMOW: Yes, there is. This is a whole discussion about what is—what is data [laughs]—and how do you make repositories, how do you convince people to put stuff in repositories, and how to do so in a way that it's actually useful.

ZIERLER: And the whole question of what's proprietary.

ASIMOW: Yes. Big discussion. Some fields, there are universally agreed-upon formats for data, and all the data goes into the repositories and everybody knows how to get it. Seismologists can just download seismograms from any seismometer in the world these days, and—well, I'm sure there's some that are not shared, but many, many, many [laughs] seismometers—and get going on the data right away, and it's just velocity of the seismometer versus time, in an agreed-upon digital format, and everybody knows what to do. Geochemical data have taken longer to get to the level of usability where there are large databases and where you know what the information in them means, and you can use it. I look with actual skepticism on a lot of the work that people do with these databases. Once you create a database and you put 100,000 rocks in it, it's very tempting to download all 100,000 rocks and try to look for the systematics of all rocks. We have here amongst the petrology faculty, loosely speaking—Stolper's group, my group, Farley's group, Eiler's group, Rossman's group—a petrology reading group every Friday. We get together and read a paper from the recent literature and we talk about it. We read a bunch of these kind of large database papers with people collecting vast numbers of samples, and this led to me formulate what has become known within the context of this group as Asimow's Second Law. Asimow's First Law was formulated by my father who was trying to get bikes off of a bike rack. It's that, "If the hook on a bungee cord can catch on something, it will."

ZIERLER: [laughs]

ASIMOW: Asimow's Second Law is that, "In any publication, the amount of thought that goes in per sample is inversely proportional to the number of samples." [laughs]

ZIERLER: [laughs] That's great. [laughs]

ASIMOW: The really good papers are the ones that manage to beat Asimow's Law and put more thought per sample than is typical. Anyway, so yeah, there are papers that have lots and lots of lots of data, and don't understand what any of it means because they haven't had the time to stop and look at the individual data points and assess whether they're accurate and whether they mean what they say they mean. Even more challenging is to make a database for experiments in petrology, because there is so much metadata that has to go along with the data for you to understand whether the experiment is good, and whether it reached equilibrium, and what it means, and which phases are present, and how they were analyzed, and what are the uncertainties. It's a difficult database problem to even describe a format into which you can put that information and then get it out, without having to go back and read the paper. Mark Ghiorso, the creator of MELTS, with Marc Hirschmann and Tim Grow, who is a petrologist at MIT, built such a thing called the Library of Experimental Phase Relations, or LEPR, and wanted it to be a standard where everybody who was writing experimental petrology papers would upload their data to LEPR as they published. It was a little bit ahead of the curve in terms of open science mandates from funding agencies, which typically now require you to do stuff like this. If you're going to use government money and you create data, you have to put it in a public repository. So, nobody really got into the habit of actually putting their information in LEPR. They had this big burst when they created it of putting legacy data in, all the data that were available up until 2005 or something, but nobody has been maintaining it.

When we contemplate calibrating new models or extensions to MELTS, LEPR is the logical repository from which we should draw the experimental database that we're going to use for the calibration, and Paula has put a great deal of effort into making this pipeline work, where we can pull information from LEPR and use it in a calibration, but it has also fallen to Paula and to our students to actually put the information in LEPR if the experiments have been done in the last 15 years, because nobody else is doing it. These kinds of things could be done better, but they take work, and that means pretty much if funding agencies and editors are not mandating that you need to put your data somewhere that is accessible, people don't. I think we're looking at an ongoing culture shift where people are accepting that this is what you have to do, and we'll start doing it, but data management plans from most of the funding agencies have only recently started to get serious. The White House Office of Science and Technology Policy has this year put out a memo that says, "We're serious about this, and there will be changes in behavior." But database science in my field has not yet really lived up to its promise. The experimental databases are not universal and portable enough to use without a huge amount of legwork, and the analytical databases are handy but have tended to be used in ways that are not all that rigorous. The other thing that is coming down the pike is applying machine learning to these databases, which means even less thought per sample from a human perspective. [laughs] Some of that will be good, and some of it will be junk. We'll see.

ZIERLER: The stories that I've heard from junior faculty, as I alluded before, about Caltech's amazing way of supporting its newest faculty members, there's a feeling of shock when they're asked, "What do you need to get your lab up and running?" and it's just like, "We'll give you what you need. What do you need?"

ASIMOW: Yeah!

ZIERLER: Which is jarring, in the sense that there isn't so much of a boundary that you know you're working in to say, "Okay, within this, this is what I really want." For you, inheriting Wyllie's lab, with only the major addition of the multi-anvil device, did you sidestep that intellectual process of wondering what you needed, or did you go all-in on this one device because you knew how much resources could be directed your way?

ASIMOW: I think I was a relatively cheap hire, compared to several of my colleagues that started around the same time that built very large new labs with all new stuff. I didn't negotiate very hard because I didn't want all that much. Also, I'm not sure I really grasped the scale of what I could ask for. But I was negotiating with Ed Stolper, who had been my thesis advisor [laughs] and was then chairman when I was hired, which changed the nature of the negotiation. Also, strategically perhaps, I'm in the unfortunate position of, it is obvious that I love Caltech. It is obvious that I am deeply loyal to the institution. It is obvious that I am never going to leave [laughs] and that I was going to come here even if they didn't make a particularly good offer. It's not a good standing from which to negotiate [laughs] aggressively! So, no, the startup negotiation was not especially aggressive. I figured out what I wanted, I asked for it, I got it. I probably could have asked for more, but whatever.

ZIERLER: Was it the fact that it was only the multi-anvil device—the other devices in the lab, they were good as is? You didn't need to do upgrades? You didn't need to add to them?

ASIMOW: Yeah, they were okay. I'm still using one of them, 23 years later. The other one was leaky and I junked it, and made extra room in the lab. What I was going to say is that the thing that is distinctive about Caltech in this regard—I have come to realize there are two things. One, there's a lot of resources available. The general budget and the endowment support spending enough money to allow people to do what they need to do. The other thing is the priority is in the right place, that when we do have resources, we direct it to the junior faculty. I was shocked, taken aback, some years later, when I got tenure, and Charlie Langmuir, who had been my postdoc advisor at Columbia and had then moved as a senior hire to Harvard, he said, "What are you going to do with your tenure bonus?" My reaction was [laughs],"What is a tenure bonus?"

ZIERLER: [laughs]

ASIMOW: Once I understood what it was, I'm like, "Why would you do that? If you have money, don't give it to the tenured faculty; give it to junior faculty, so that they'll get tenure!" It's part of our system that I know exists in this Division and I suspect across the Institute, that when we hire junior faculty, we hire them with the intent to give them everything that they need to succeed and become tenured faculty. That's our job, as senior faculty, is to mentor and cultivate the next generation. I get the sense that at other institutions, that's not so true. You hire junior faculty on a trial basis, and if they don't succeed you throw them away and hire new junior faculty. We don't do that. As a result, we're very careful, maybe too careful in our searching. We can be really slow to hire anybody because we want to make sure somebody's a superstar before we get into the position of maybe having to deny tenure to them someday. But once we do commit to someone, we really commit. I certainly value that. I certainly experienced that as a junior faculty member. I got everything I wanted. And, I felt like I was not on trial like they were hoping I would fail, or wondering whether I would fail; they were there to cultivate and nurture and mentor me and see that I succeeded.

Now that I'm on the other side, I think this is my job, to the extent that I get to direct resources—which is not that much because I'm not the chair or the director of any institute or anything like that. But when we have, for example, the prize postdocs and the option postdocs, where we have one year of support for a postdoc, anybody can mentor the postdoc but if it comes down to a tie in terms of the quality of the candidate and the quality of the proposal between somebody who is going to work with a junior faculty member and somebody who is going to work with a senior faculty member, the junior faculty member wins. That's what that money is for. It's to help people get going. Speaking of which, the hard money postdocs—I mentioned this before in the context of applying for postdocs and what kind of postdoc you want—from the point of view of a faculty member, the fact that Caltech has funding for lots of hard money postdocs is really useful. Because I very rarely think, "Oh, okay, I'm going to write a postdoc salary into my grant to do this particular thing, and then I'm going to get the money six months after I write the grant, and then I'm going to try to hire somebody to do that." I would much rather have somebody talented apply for one of our prize postdocs, get a year of hard money, then they're here and we can talk and say, "What do you want to do? That's a good idea. Let's write a proposal to fund your second and third year." That's a much better model, and it's only possible because we have the Texaco fellowship and the Earl fellowship and the option postdocs and the Barr Foundation fellowship and all of these sources of funding that allow us to bring in a postdoc before we've written the grant to fund the postdoc. It's better.

ZIERLER: The multi-anvil device, was that sort of an island without Wyllie's lab? In other words, when you look at Wyllie's lab, did it need the multi-anvil device to complete it, in terms of its intellectual purview, or you would have brought that in no matter whose lab you inherited?

ASIMOW: Peter's emphasis was on crustal petrology, things that happen at depth in the Earth but relatively shallow by my standards. He didn't need to extend his experiments beyond about, say, 3 GPa, because that just wasn't the kind of problems he was working on. I wanted to work on deeper mantle problems; I needed the multi-anvil device. At the same time, I also work on low-pressure problems, so I like having access to the full range of capabilities from one atmosphere up to multi-anvil pressures. If I hadn't taken over Peter's lab, in addition to buying and installing a multi-anvil device, I probably also would have bought and installed a piston-cylinder device and a rapid quench cold seal apparatus for 0.1, 0.2 GPa kind of pressures. Then I've been able to take advantage of being on the same floor as Ed Stolper and his lab, to not have to build my own one-atmosphere gas mixing furnaces, which are very useful for things that don't require the application of pressure but just high temperature, accurately knowing temperature, and controlled chemical environments. Because John Beckett and Mike Baker have kept that lab in tip-top shape for all these years and allowed me to walk in and use it whenever I want. The third floor of Arms here, with the Stolper labs, the Rossman labs, and my labs, somebody owns every room, but it's all effectively shared space. We all go in and out of each other's rooms all the time. At one point, all the Stolper tools were painted with blue and yellow stripes, and all the Wyllie tools were painted with green and yellow stripes, so that things would eventually make their way back to the right room.

ZIERLER: Wait, what are your colors?

ASIMOW: I never really made up a color.

ZIERLER: [laughs]

ASIMOW: The advantage of this is that I've been here long enough, I know where everything is, and I can hack together an [laughs] apparatus, to MacGyver essentially anything that needs doing. The disadvantage is, I can't do anything without going in and out of six different rooms. [laughs]

ZIERLER: [laughs] That's great.

ASIMOW: But yeah, this shared facility is extremely useful for accomplishing lots of jobs and being able to make up a new experiment without too much planning, because there are so many spare parts sitting around.

ZIERLER: The last topic we'll cover today—we talked about computation, we talked about instrumentation and lab work. When you got hired as a faculty member here, what opportunities were there in fieldwork, in being a field geologist? How did you want to pursue that right out of the gate?

ASIMOW: Didn't have any plans to do that right out of the gate. I was hired as assistant professor of Geology and Geochemistry, because my degree is in geology, from here [laughs], so it made sense. But, all my research agenda was focused either on computations or experiments, or going to sea and actually picking up glass from the mid-ocean ridge.

ZIERLER: You continued that work, from here.

ASIMOW: I started that relationship with Langmuir at Columbia, and a few years after I got here, I was invited to participate in a research cruise and do that.

ZIERLER: This was summers, mostly?

ASIMOW: No, the cruise that I went on was in the fall, in 2004, and it was just a one-off thing. I did that once. It was really interesting, a really different lifestyle to be out at sea for 36 days and not have to commute to work, and not have to get your kids to school, and not have to cook your own food, and just do your shift, get enough sleep. It was a really interesting different kind of lifestyle and I enjoyed it for that month, but I haven't gone back to do it again. Fieldwork was a thing that I did, apart from that one cruise, really just for teaching purposes, to inspire students to appreciate the Earth and what you can learn by going out and looking at things. I didn't really do any field-based research for a lot of years. Then a couple of things happened. First collaborators started coming to me who had done fieldwork in some place in the world and had interesting samples but either needed my expertise to model what those data meant or needed the analytical facilities that we have here and ready access to, to analyze the rocks they brought back and generate the data, which could then be modeled. So, every now and then, somebody will write to me and say, "Can you help? This is my research project." Most of the time I have to say no, but sometimes I say yes.

Maybe 20 years ago now, a PhD student in Greece named Ioannis Baziotis, asked for help modeling his rocks from Greece, and they were interesting rocks, and he had at least made a start, and I was able to help him, and that has turned into a 20-year friendship and professional relationship now. He finished that work. He finished his degree in Greece. There were no professional opportunities in Greece. It was one of their periodic economic crises at the time. He applied for a postdoc with Larry Taylor at the University of Tennessee Knoxville doing meteoritics. Actually Taylor was mostly into meteorites but he was also working on igneous rocks from Earth and he needed a postdoc to do that. I wrote a very strong letter, and Larry Taylor called me up and said, "What's with this Greek guy?" I said, "He's good. Hire him." And he did. That actually helped Baziotis move into meteoritics which is most of what he does now. That has been a very fruitful collaboration and friendship, and again, it started when he had the temerity to email me and say, "I'm trying to do these MELTS calculations and they're not working. Can you help?"

Accidental Expertise in Egyptian Geology

In 2014, an Egyptian geologist, Mokhles Azer, wrote and said, "I've got money from the U.S. Agency for International Development to do a postdoctoral visit to the U.S. Would you host me?" Turns out, by the way, that this is still an ongoing echo of Camp David; we send more money to Egypt than we otherwise would. It sponsors things like professional exchanges of scholars. Azer came here, and turned out his spoken English was abominable and we couldn't communicate in person all, so I just said, "All right. You brought these rocks, let's analyze them, and then take the data home and analyze it, work it up and write the first draft of a paper, and we'll communicate in writing." That has worked really well. We have like 30 papers now.

ZIERLER: Wow!

ASIMOW: So I have become one of the foremost experts on the geology of the Arabian-Nubian Shield, which outcrops in the Eastern Desert of Egypt between the Nile and the Red Sea, and also on the other side in Saudi Arabia, just because Azer does all this fieldwork, he picks up all these rocks, he sends them to me, and I analyze them, and he writes up the first draft of the paper, and then I edit it and put in some modeling, and we publish it. They aren't all the greatest papers, but that whole thing got going just because I said yes to this offer to host him. I haven't been to Egypt yet. I was going to go in 2020. Haven't spun around to doing that again. But from this experience, I started to get this feeling like, "Okay, I'm working with all these field geologists, I'm analyzing all these rocks in the laboratory; I should go! And get my boots on the ground, and see these places, and see what I'm missing by just waiting for somebody to send me rocks."

In 2017, I guess, I happened to mention to a postdoc here, Forrest Horton, that I had looked out the window of an airplane while flying over Baffin Island in Arctic Canada and seen a perfectly circular lake that might be an impact crater. He said, "That's cool. Let's go." So we wrote actually a grant to National Geographic, which is not one of my usual funding agencies by any means, but they thought this seemed cool, to get a helicopter and go out to this site, on a headland between a couple of fjords in Baffin Island, and see if it's an impact crater or not. Meanwhile, Forrest got hired as an assistant scientist at Woods Hole, and as part of his startup package there, he got more money for them to extend the expedition. Because within helicopter range from the site of this putative impact crater is an outcrop of rocks that are really famous amongst geochemists because they appear to have the purest sample of geochemistry that we associate with the lower mantle of the Earth. Of all the rocks on Earth, these basalts on Baffin Island appear to be the purest samples of lower mantle. That's kind of cool.

We had enough helicopter time for eight days, four to go see this impact crater, and four to sample these basalts. Forrest, and Joe Biasi, a grad student here, and I, went up there in 2018, during the very short summer season between when the snow melts and when it starts snowing again. We got to the impact crater site, and it was obvious within hours that there was nothing to see; it was just a round lake. [laughs] Complete waste of time. Beautiful place; not an impact crater. But then we had seven and a half days to really do a good job sampling these geochemically interesting basalts. Everybody else who had ever gone there arrived by boat and had to walk all the way up the hill and carry the rocks all the way back down so they mostly just picked up rocks from the bottom of the cliffs, out of place. We had a helicopter so we could put down on the top of every hill, and fill our backpacks with samples, stratigraphically controlled, shielded from cosmic rays, really nice sample collection. We're still working on that. It was while sitting out on this island looking across the Labrador Sea towards Greenland as the icebergs go by, with our Inuit man with his rifle looking out for polar bears, that I remembered, really, why [laughs] I became a geologist in the first place. I'm like, "This is the life. I would love to do more of this." And get out of the lab as much as I can.

Another of these students that every now and then somebody writes to you and says, "I need help"—there was a PhD student in Cameroon, in west central Africa, Jonas Takodjou Wambo, who wrote to me and said, "I have this rare opportunity. Most of southern Cameroon is covered by meters of soil. It's very deeply weathered. You can't see the bedrock. But they're building a dam, and they've excavated all the soil away and exposed the bedrock, for now. Then they're going to build the dam and they're going to flood it, and it's going to be gone. These are the rocks there, and this is what we can see, but I will need help to analyze the rocks in order to make sense of this outcrop." I thought it seemed like a really worthy project, so I started collaborating with him. Again, he sent me the rocks, we analyzed them here, I sent back the data. Then there was this tragedy where, because they were also looking for gold, bandits came in and took everything from their lab, and their homes, all their hard drives, all their computers. But I had backups of everything here, so I was able to rescue his thesis. Then he finished. Also in Cameroon, everything is connections and not talent, and he couldn't get a job, and we had these hard money postdocs, and the person that we offered the geochemistry postdoc to turned it down, so we were kind of off schedule, and I swooped in and I said, "Okay, this is unusual, but I would like to hire this postdoc from Cameroon to come here." My colleagues said, "That sounds like a good thing," so we did. His project started with field work in Cameroon, so I said, "I'm going. [laughs] I want to see the place. I want to participate." It made the expedition much more complicated and expensive to take a white guy, a white vegan guy, out into the far outback of Cameroon. We had to have armed guards from the army. We had to have a cook from the capital. We had to have professional drivers. But that was a really cool expedition, and we picked up a bunch of rocks. Jonas is here, and we're working on them now. I would love to do more of this kind of stuff, either in collaboration with geologists around the world, or just because we think of a place that would be cool to go. Field geology is—fun, but it's also hard, to take the observations that you can make, just with eyes or with a drone or by picking up rocks, and learn something really new and original. You at some level can have a much bigger impact by doing theory or by doing experiments that in principle apply to any terrain in the world, than you can by working on one particular terrain, unless you choose your places to go, very carefully, to be the best example of something. But I have the time and leisure to do all these things, so that is my goal.

ZIERLER: Last question for today. As a junior faculty member, you were focused on computation and lab experiments, not yet on field geology. It does raise the question, does that mean that you were working on samples from other field missions, or were there aspects of your research that didn't require samples at all that were divorced from the physicality of finding rocks and analyzing them?

ASIMOW: Yes, at first mostly that. The thermodynamic calculations are rooted in experiments, and they can be used to interpret rocks, but they can also be used to interpret processes that are pretty far divorced from the rocks. If we're trying to understand things like the Moon-forming impact and the melting of the whole mantle and the crystallization of the magma ocean, and these very large scale, very long ago processes for which there aren't any samples, part of doing the theory is figure out, does the theory eventually make a prediction that is specific enough that there might still be evidence of it on the Earth to go and pick up? Maybe no, and it might be less satisfying if the theory is never really testable. But you have to have the theory to figure out what the tests might be, before you can do the tests. A lot of the work that I was doing let's say after—after I published everything that I started while I was a postdoc, dealing with mid-ocean ridge basalts, and before I started working on the rocks from Greece and Egypt and Africa—in between, that ten-year period or so there, it's very much separated from any actual rocks, because it was mostly about the deep mantle, and the deep mantle is inaccessible, except by geophysical measurements, which is very different from picking up rocks.

ZIERLER: On that note, next time we'll pick up in the narrative when you came up for tenure, and what case you made at that point, what your contributions were. Then, the process of being more involved in Tom Ahrens' lab and ultimately taking it over. We'll pick up on those two. If they're interrelated, we'll cover that as well.

ASIMOW: We should also get to the non-research stuff that I have done, in terms of committees that I've been involved in—student housing; freshman admissions; Diversity, Equity, and Inclusion in the GPS Division. A lot of my time and effort goes into things that have affected and will affect the history of the Institute that aren't exactly research.

ZIERLER: I wonder if, just thinking chronologically, if a lot of those administrative interests and responsibilities came after tenure? Or you even did some of those things as an assistant professor?

ASIMOW: We try to spare our assistant professors overwhelming administrative work, but we do sit on some committees both in the Division and in the Institute and may gain some leadership and some influence, as long as it's not taking too much of your time.

ZIERLER: Okay, research and administration, next time. Very good!

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Tuesday, May 23rd, 2023. It's great to be back with Professor Paul Asimow. Paul, once again, thank you for having me in your office.

ASIMOW: You're welcome. Thank you for listening!

Taking Over the Shockwave Lab

ZIERLER: We're going to pick up today in the turn of the century—sounds like a time ago—late 1990s, early 2000s. Tell me about your increasing interactions and involvement with Tom Ahrens, ultimately leading to essentially you taking over his lab. First, tell me about Tom and his research, what he represented in the field.

ASIMOW: Tom started at Caltech in I think 1966, coming from Stanford Research Lab, and he really was one of the first people in the United States that had the idea that explosives or ballistics or guns could generate strong enough shocks to help us understand planetary impacts and the properties of materials at high pressure, for geophysics.

ZIERLER: This was a truly original idea from him?

ASIMOW: It was happening in Russia. In addition to the Russian military establishment blowing things up for military purposes, there were physicists in Russia studying the properties of shocks to understand material properties and to some extent planetary materials. But Tom was really a pioneer in planetary surface science and using experimental shock waves to understand impact craters, and then somewhat later in using shock waves also to study the properties of geophysical materials to understand planetary interiors. Tom was a professor of Geophysics and Planetary Science. His first lab was at the old Seismo Lab facility in the San Rafael Hills. When South Mudd was built in 1974, the sub-basement was basically dedicated to making a space for Tom, and the original two-stage light gas gun, his workhorse instrument, was very large and ran basically the whole length of the south wing of the building. It was later miniaturized to a certain extent. Now it runs about two thirds the length of the building! [laughs] Tom was an amazingly productive scientist. He wrote hundreds and hundreds of papers with many coauthors on many subjects ranging from impact cratering to the geophysics of planetary interiors to more materials science sort of topics like using shock waves to consolidate powders into solid materials, discovering new phases that occur at high pressure. He trained a generation of students and postdocs, many of whom went off to other universities or to the national labs, which all have—not all; Sandia and Los Alamos and Livermore study shock waves.

ZIERLER: Those are the weapons labs, not coincidentally.

ASIMOW: For weapons reasons, but, the weapons labs know that a lot of talent is interested in pure science problems also, and finds ways for them to continue to work on those subjects. I've had a long-term collaboration, once I inherited the lab, with Lawrence Livermore National Lab, and there are people—I'm not doing anything classified; if I were, they probably wouldn't tell me—but we're working on Earth science problems because that's what I want to do, and they like to collaborate on that.

ZIERLER: If we can go back to the original point you made—

ASIMOW: We will.

ZIERLER: —which was really interesting, about—first of all, the Russians and the sixties—is this all made possible because of Sputnik, about basically turning space into a laboratory? Is that sort of the foundation point of having this idea that simulated explosions on Earth might tell us about collisions in space?

ASIMOW: I can't draw a through-line from Sputnik to that. Already from standing here on the Earth looking up through a telescope, you can see that the Moon is peppered with impact craters, and that from studying impact craters on Earth, like Meteor Crater in Arizona—Gene Shoemaker had already worked out that things hit the Earth and generate transient high pressures and generate high pressure minerals and damage the rocks, and somehow we have to figure out, if we see a certain size hole in the ground, can we reconstruct, how big was the thing that made it and how fast was it moving. There's a hard scaling problem from what you can do in the laboratory at micron, millimeter, centimeter, maybe meter scale if you're ambitious, up to 100-meter, 100-kilometer scale, like we see on planetary surfaces. That's a hard problem. So, yes, the whole space program and planetary exploration program, one of the things you see when you go to other planets is that they're always running into each other, so there's a connection. But rocketry and ballistics developed along rather separate courses, as far as I know. People like von Kármán, who were trying to get intact things off the ground, and people like Tom who were [laughs] blowing things up for the glory of science; I don't know that they really had much overlap.

ZIERLER: What was Tom's training?

ASIMOW: Physics, I think. I don't know that he ever had any actual training in Earth science. I think he stumbled into that as an application of what he could do with his knowledge of physics and his military training. He was in the Army in the sixties.

ZIERLER: Ah! I figured there must have been that connection.

ASIMOW: I didn't work with Tom when I was in graduate school. I was doing other things. But, at some point, I encountered the idea that the thermodynamic path that a material follows during a shock wave experiment is start at ambient pressure and temperature, undergo a very rapid step in pressure, temperature, density, internal energy, to some high pressure and high temperature state, along a family of states we call the Hugoniot, which are the series of states you can get a material to with increasingly strong shocks. Although a material does not actually go up the Hugoniot; it goes up a straight line in pressure-volume space called the Rayleigh line, to a point on the Hugoniot. It spends some amount of time there in the shock state, and then, because we're shocking finite size things, which have edges that are in contact with vacuum or atmosphere, it's not going to stay compressed forever; it's going to release. A wave is going to come in from the free surface and allow the material to expand again back to ambient pressure. Shock waves are irreversible compression steps, whereas the release wave is essentially a regular acoustic wave. It's not hypersonic relative to the material it's traveling into. It's not a jump in physical properties. It is approximately an isentropic release path coming down towards low pressure, low temperature, low density, at approximately constant entropy. That caught my attention, because what I had been studying for my thesis and a lot of my work on understanding melting in the mantle was constant entropy decompression. Constant entropy for a very different reason, the reason being we're talking about enormous masses of rock, hundreds of kilometers in scale, moving at centimeters per year, which is too fast for heat flow to matter. Now we're talking about millimeters of material, decompressing at kilometers per second, but again it's too fast for heat flow so it's still an adiabatic change of state, but approximately reversible. Experiments that could actually test what the thermodynamic models were saying should be happening during mantle decompression were very hard to come by, because conventional static experiments control temperature; they don't control entropy. So there isn't a good way to do an isentropic or adiabatic decompression. So, I just casually asked Tom, could we use the release from the shock state as a way to test my theories about melting along constant entropy paths?

ZIERLER: This was during graduate school you asked this question, or as a faculty member?

ASIMOW: This was just about the time I graduated. It might have even been in response to a question after my thesis defense. It was right there. Because independently, we were both aware of and had methods for calculating this idea of isentropic release of rocks across the melting path, across the melting curve. But that was the seed that Tom needed [laughs] to solve his problem, which was that he was coming to the end of his very successful career, he had this big lab, and he didn't want it to end with his retirement. He wanted to leave a legacy of ongoing research in shock wave experiments in geophysics and planetary science. The best way to do that would be to find a young member of the faculty interested in collaborating and eventually taking over the lab.

ZIERLER: What was his answer to your question?

ASIMOW: "Yes. Potentially we could do that. Let's write a proposal to do it." So, while I was a postdoc, I started participating in Tom's proposal writing exercises, initially at kind of the lowest level, which is co-investigator. A proposal has a principal investigator, co-principal investigators, and co-investigators. The co-investigator is not a very big commitment. But we wrote a proposal. I think it was funded. So, when I got here and started up as a faculty member, I started attending the regular lab group meetings of Tom's group. We also early on—I mean, really in my first year—we started co-advising an excellent student, a geophysics student named Sheng-Nian Luo, who really was a good physicist, and very ambitious, and very energetic, and did a lot of things. By the time he graduated, there were half a dozen interesting papers. So there was this first idea that we could study isentropic decompression and maybe get some understanding of the analogous but much slower process in the mantle. That didn't work particularly well because of kinetics. Slow isentropic decompression in the mantle follows an equilibrium path. Rapid isentropic decompression from a shock state in the laboratory is very likely to follow a path that is limited by reaction rates and kinetics, and not the equilibrium path. Under some circumstances, there's something to that idea. It wasn't in the end a great idea, but it's what started the whole thing.

What really built into something successful in those early years was in my other lab here, where I took over Peter Wyllie's space, I installed a multi-anvil device which can reach very high pressure. One of the problems with shock waves for doing deep Earth geophysics is it's easy to get high pressure—comparatively easy; you launch a fast projectile—but when you hit things hard, they get very hot, hotter than the temperature in the Earth at the equivalent pressure. So you're always having to make a correction to the data that you measure in the laboratory to what you think it says about similar pressures but substantially lower temperatures. But there are ways to modify shock compression experiments to access lower-temperature states. Also there's ways to modify them to access higher-temperature states, which we'll get into later. The best way to do it is to do most of the work of compression before the shock. One way to do that is synthesize dense minerals, the minerals that occur at high pressure in the interior of the Earth, recover them to ambient conditions—room temperature, room pressure. They are metastable; they would love to convert back to the low pressure phase, but they don't have time at room temperature. And so, in my static high-pressure lab, I can make quality specimens of high pressure minerals, then I can slice them to the right shape, load them into the shock wave gun, and impact them, and access conditions that are otherwise very hard to get to.

We started doing that. We started with the silica system; quartz is the stable phase at ambient pressure. If you compress quartz to a certain pressure it converts to a denser mineral phase called coesite. We can easily make lots of coesite in the piston-cylinder apparatus. More challenging, because it requires substantially higher pressure, is stishovite. Stishovite has a very interesting history. It was one of the first predicted and then experimentally synthesized and then discovered in nature high-pressure minerals. This comes back, like many things, to Thompson. There was a famous geophysicist at Harvard named Francis Birch, and Birch wrote some really influential papers about trying to figure out the interior structure of the Earth with very early seismic data and theory, basically. In one of his papers from the fifties, he says, "I thank James B. Thompson for pointing out the possibility of rutile structured silica." Thompson just understood enough about mineral structure and coordination environments that he reasoned that SiO2—where you have a silicon plus-four cation that's surrounded by four oxygens—if you squeezed it enough could adopt the same structure as TiO2, titanium dioxide, where titanium four-plus has six nearest oxygen neighbors and therefore is a much denser structure. At ambient pressure, silicon doesn't fit in the rutile structure, but he reasoned that if you squeeze it, it would. Then, in the early 1960s, Sergey Stishov, with a high-pressure apparatus in Russia, synthesized this material, rutile structured silica, and then very shortly thereafter, Shoemaker and Chao found it in the debris from the Meteor Crater impact in Arizona, and named it stishovite, after Stishov who first synthesized it. Then it became a mineral, because it occurs in nature, and we don't call it rutile structured silica anymore; we call it stishovite. This has since then happened many times with materials that we knew existed but they weren't minerals because there were no natural specimens, and then somebody finds a natural specimen and we name it and it becomes a mineral. Stishovite is harder to make, but we made it, and we shocked it, and with Tom and with Luo, we published several papers on the high-pressure properties of silica at low temperature obtained by shocking coesite and stishovite. Those were good papers, and it was fun to do them, and it combined what I could do here in the static high-pressure lab with what Tom could do in the Shock Wave Lab.

How to Measure Temperature in the Deep Earth

ZIERLER: A background question—your sensitivity to the anomaly of the deep Earth temperature, that it would not be the same, it would not match in the laboratory, how do we know the temperature at a given place in the Earth? How do we figure that out?

ASIMOW: We have several ways. This is the question that I pose to prospective students when I'm giving tours of the Lab to pre-frosh that are on campus, to try to explain, at the most fundamental level, what you can do with a shock wave experiment. How do we know the temperature of the center of the Earth? It turns out, from seismic observations and cosmochemical concerns and various lines of reasoning, we know that the Earth has a core, we know that the core is dominantly made of iron, we know that the outer core is liquid, and we know that the inner core is solid. From those facts alone, we know that the boundary between the outer core and the inner core must sit on the melting curve, or close to the melting curve, of iron, at the relevant pressure. The relevant pressure at 5,150 kilometers deep, the boundary between the inner and outer cores, is 3.3 million atmospheres, 330 gigapascals in my preferred units. If we can measure the melting temperature of iron at 330 gigapascals, we know the temperature at that depth, and once you have one sort of tie point, you can work down to the center of the Earth by adding adiabatic compression of the inner core solid. You can work up to the core-mantle boundary by adding adiabatic expansion of the outer core fluid, so you can get the temperature on the core side at the top of the core. Meanwhile, from seismic velocity of the mantle and the fact that the mantle is solid, we can constrain the temperature of the mantle and work down, and compute how big is the temperature contrast across the core-mantle boundary. So it comes from seismology, making observations of where it's solid, where it's liquid, and what are the wave speeds, and then it's all calibrated using high-pressure experiments, especially shock wave experiments, so that we can tie those observations of sound speed or melting points to pressure-temperature conditions.

The shock wave experiments have been really influential. They have always been able to get to higher pressure than static experiments at any given time. The ability to measure the melting curve of iron under core conditions was done first with shock wave experiments, and then the static methods like the diamond anvil cell eventually caught up. Unfortunately, the first generation of papers that measured the melting curve of iron by shock wave experiments, one of them was bad, and people still put that data point on their figures, [laughs] and so it makes it look like there's more scatter, more uncertainty in our knowledge of this property than there really is, if you simply cross out that one data point and say, "Okay, this was a first try. This was bad." I wish people would stop putting that data point on their figures. The combination of geophysics and mineral physics allows us to constrain the temperature in the Earth, and it allows us to—also, kind of from first principles, compression in the Earth, once you get below the lithosphere, is adiabatic, whereas shock wave experiments are irreversible. They deposit extra irreversible work during the rapid compression and that's necessarily going to make them hotter.

ZIERLER: This line of inquiry is what would explain why Tom Ahrens would be a standing member of the Seismo Lab? He was not an earthquake scientist but what he was doing was really of great value to seismology? Or he was really using seismology and that was of great value to his work? Or it was really a two-way street?

ASIMOW: Absolutely two-way. Seismologists can only measure wave speed. If they're happy with just reporting wave speed, then that's fine, but if they would like to further interpret their wave speed in terms of the composition and thermodynamic state of the deep interior, they need mineral physicists to do the experiments to reproduce the wave speeds that they are seeing and tie it back to particular materials under particular conditions. That's one of the main missions of the science of mineral physics, which to a significant extent was developed here in the Seismo Lab by Don Anderson, his students like Bob Liebermann, as well as Tom. So, yeah, they needed each other.

ZIERLER: The question that you initially posed to Tom, was that the gun that you would use for this? Is that what he had that would answer the question?

ASIMOW: Yeah.

ZIERLER: Tell me about the gun. What did it look like? What does it look like? How did he build it?

ASIMOW: [laughs] The lab has four guns. Two of them are what we call single-stage propellant guns, and two of them are light gas guns, two-stage guns. A single-stage propellant gun is pretty much what it sounds like. It's a metal tube of a certain length with a place at one end where you can load and detonate gunpowder, and a place at the other end where you can put a target that you want to run a projectile into.

ZIERLER: So, "gun" really is the right term for what this thing is?

ASIMOW: Yeah. Tom's early guns were recycled military hardware, basically cannons of one type or another. The breech end of one of the guns that is currently in the Lab is in fact the breech of a World War II Naval deck cannon. The rest of it at this point—it was custom built for scientific applications. A single-stage gun is very simple to operate. All you need is some gunpowder [laughs] and some safety protocols and a projectile. They are limited in the speeds that they can reach, simply because of the properties of the way gunpowder burns and transfers momentum to a projectile. It is very hard to get a projectile going much faster than 2,500 meters per second by simply burning gunpowder. Now, 2,500 meters per second will get you pretty high pressure on impact. If you launch a hard metal projectile, it will get you 50 or 60 GPa, so any upper mantle pressure and some distance into the lower mantle. There's lots to do in that pressure range. Over the 40, 50 years lifetime of what we call the 40-millimeter gun, which is the big single-stage gun—done something like 1,200 experiments, to study the properties of materials at high pressure but not that high.

We also have a 20-millimeter single-stage gun which we predominantly use for recovery experiments, which is to say, we put the sample in a chamber, we launch a projectile at the chamber, which drives a shock wave through the chamber but doesn't break it, and then we can take the chamber to the machine shop and slice it open and see what's left inside. We use that, and Tom did a lot of these experiments too—over 1,000—to study shock metamorphism of meteorites and impact target rocks, and also to synthesize novel materials. Basically to be able to study at leisure what you did with the shock wave, after the shock wave. On the bigger guns, we don't recover anything—everything is blown away—and so it's real-time observations of the shock propagating through the sample that we make.

For the really high velocities, if you want to study the lower mantle or the core—and remember we were talking about constraining the temperature of the core, which means melting iron at very high pressure—you have to get the projectile going faster than two and a half kilometers per second. You need three, four, five, six, seven, maybe even eight kilometers per second. That requires—or at least that can be done with—a two-stage gun. The idea of a two-stage gun is the combustion products that you get from burning gunpowder are full of heavy molecules which give you a relatively slow sound speed in the gas, which gives you relatively inefficient coupling of momentum from the compressed gas to a solid projectile. The opposite end of the spectrum is hydrogen. Hydrogen is the lightest gas; it has the highest sound speed at a given pressure. As it expands, it is very efficient at having lots of waves reflecting across the mass of expanding gas, each one of which gives a little kick to the projectile. So, if you can get hydrogen to high pressure, you can use it to launch a projectile very fast. The way we do that is we get a two-stage gun. In the second stage of the gun is a projectile sitting in vacuum waiting to be launched. Between the two chambers of the gun, there is a valve, a single-use rupture disk that has been machined to break at a certain pressure. Upstream of the rupture disk is what we call the pump tube, which is prefilled with some amount of hydrogen gas. Upstream of the hydrogen gas is a piston, which will compress the hydrogen gas when it travels. Upstream of the piston is the main gunpowder charge. We use a lot of gunpowder, something like a kilogram, because the piston is pretty heavy and we want to get it going pretty fast. The energy that eventually is going to launch the projectile starts out as chemical energy in the gunpowder, we burn the gunpowder, convert it to kinetic energy in the piston, the piston compresses the hydrogen gas, converts it into elastic energy basically, and when the rupture disc breaks, then the hydrogen gas expands and launches the second-stage projectile, and it can get up to 7,500 meters per second and we can get really high-pressure impacts. I don't know the early history of light gas guns, who invented them, who was the first to use them for this purpose, but—

ZIERLER: This would have been a generation prior to Tom, or he would have been part of that founding generation?

ASIMOW: Don't know. In terms of applying this instrument to what Tom was doing with it, he was the first generation. So there was a—there is, still—a company in Ohio, Physics Applications International, that builds light gas guns for scientific research purposes. When the big lab in the sub-basement of South Mudd was built, Tom bought a two-stage light gas gun from Physics Applications International. The original gun was very big. The pump tube that compressed the hydrogen was almost a foot in diameter and probably 15 meters long. At some point, they redesigned it. They worked with an engineer named Mo Shahinpoor, who came up with an equivalent performance design of the pump tube that is only three inches in diameter and six meters long, so it got a lot smaller and a lot cheaper. You don't need as much hydrogen, you don't need as much plastic in the piston, you don't need as many men to load the thing, because it doesn't weigh as much and it takes up less space. That conversion of the light gas gun happened before I got here, maybe in the eighties sometime. You also need a lot of ancillary equipment to do something useful with these projectiles once they get going. You have to know how fast they're going. You have to be able to observe the impact with high-speed cameras or detectors of some kind.

There's a very useful instrument called a streak camera, which basically originally was a big hoop of film with a very rapidly spinning mirror in the middle, and the mirror is spun with like a jet of compressed air and a fan, a turbine, that gets it going at some thousands of RPM. The lab is dark. When the shock wave is about to happen, you set off a bright flash that reflects off the back of the sample, off the spinning mirror, and records a streak on the hoop of film, that when you unroll the hoop of film, time, along the film, and position across the sample, across the film, allows you to see a recording of what happened. Analog streak cameras can go pretty fast, millimeters of film per microsecond of time. If you want to go even faster, if you need millimeters per nanosecond, you can't spin a mirror fast enough, so you have to switch to what's called an image converter streak camera that has a very narrow slit in the lens, so at any given time there's just one line of light. It converts it from light into an electron beam, and then the electron beam can be swept with a varying voltage plate before it strikes a phosphor and is converted back into light. Then the originally film and now CCD records that light on the phosphor screen. Again you get position down the film—or, time—down the film, and position across. But you can go way faster. Tom bought an image converter streak camera maybe around 1990, and then they kind of stopped making this model of camera, and everything got miniaturized. There are still streak cameras, but ours is sort of the last one operating of this generation of very large-format streak cameras that have a very long imaging tube that allow us to record for a pretty long time, at a given streak rate.

ZIERLER: This is an analog camera?

ASIMOW: It was originally an analog camera. It recorded on film. Originally, wet film, and we had a darkroom, so after an experiment, you would take the film cartridge, go to the darkroom, develop the negative, print it, and then the next day you'd know whether the experiment worked. Then, we realized you could do it on Polaroid film; didn't need for most purposes the darkroom at all. With Polaroid film, you find out five minutes after the experiment whether the experiment worked. But then Polaroid stopped making film, and after a few years, it was all expired. There was this period where we were rushing around trying to find boxes of unexpired Polaroid film, and experimenting with Fuji instant film and things like this—it was a crazy period—before we finally said, "Okay, we need to get a digital camera."

ZIERLER: When did charge-coupled devices enter the scene?

ASIMOW: In our case, I made the conversion of the streak camera from Polaroid film to a CCD back when I had to [laughs], when you could no longer get Polaroid film. That was probably, I don't know, 2008, something like that, so by the time I was in charge of the lab.

ZIERLER: In astronomy, they adopt CCDs for the night survey telescopes a decade earlier. This happens in the nineties. Was that—?

ASIMOW: They had more money to play with than we do.

ZIERLER: My question is, was your adoption coming from the astronomers? Is that where you appreciated the value of the CCDs?

ASIMOW: No. Everybody everywhere in photography was converting to digital. Film was clearly on its way out. You couldn't get it anymore. I just needed to wait until I could get a big enough CCD to take advantage of the very large imaging tube in my streak camera without giving away resolution. So I needed to wait until CCDs that I could afford got big enough to give me enough pixels along the streak direction to make it worthwhile. I waited as long as I could [laughs], as CCDs got bigger and got cheaper, until it made sense to do that conversion.

ZIERLER: Another parallel story in astronomy is that when they adopted CCDs, there was a proliferation of data. There was just so much more data that was coming in. That's when they started to adopt AI, because you need to figure out how to deal with all this data. The same for you? Pardon the pun; was there now an explosion of data as a result of adopting the CCDs?

ASIMOW: No, no. The amount of data we generate is limited by the number of times we can shoot the gun. A record of the experiment on film versus a record of the experiment in a digital file is really very similar in terms of the amount of effort and work it takes to process and archive it. We're not open all the time just collecting photons; we're collecting photons for 100 nanoseconds. Whether we collect them on film or on the CCD, we're not going to be able to collect more photons.

ZIERLER: Generally, these are, relatively speaking, low-data experiments?

ASIMOW: Yeah. We're able to cut out the step of having to digitize the film in order to do image processing on it, because it's digital to begin with, so it's less work, not more.

ZIERLER: You mentioned taking a portion of this experiment to Wyllie's lab. Were you the intellectual bridge between Ahrens and Wyllie? Had they collaborated before you?

ASIMOW: No.

ZIERLER: What did you need from Wyllie's lab that wasn't achievable with Tom Ahrens?

ASIMOW: There was a sort of connection, not with Wyllie but with Stolper. Starting in the 1980s, Tom and Ed Stolper began collaborating on using shock wave experiments to measure the properties of magma at high pressure. Tom had primarily been working on minerals, on solid materials, or on finding the melting points of those materials. But igneous petrologists, people who are interested in the behavior of molten rocks, the biggest shortcoming in our ability to model the behavior of melting at very high pressure is the physical properties of the liquid. It is harder to measure liquids than solids, because most of our knowledge of how solids compress comes from diffraction experiments, and liquids don't do that. Ed had an interest in the density of magma at high pressure, and whether, if you squeeze magma enough, it becomes denser than the coexisting liquids and drains downward, instead of draining upward and erupting as a volcano. He had kind of reached the limits, at that time, of what you could do studying this with static compression experiments.

Somehow, and I don't actually know how this idea was hatched and got off the ground, Tom and Ed realized that they could synthesize a glass of the composition they were interested in, they could get a piece of equipment from Lee Silver which he originally bought for melting zircons for geochronology and use it to heat the glass above the melting point in a capsule, and then drive a shock wave through the capsule and out again, watch the travel time, work out how much of the travel time was in the capsule and therefore how much was in the liquid, and use that to get at the properties of liquid at high pressure. Very ambitious experiment. It originally was the thesis research of a student named Sally Rigden, who wrote three papers in 1984, 1988, and 1989, using this method, on the 40-millimeter gun, so at relatively low pressure—five, ten, twenty. The highest pressure experiments were about 25 GPa. There was another student named Greg Miller who did similar work on another composition in the same sort of pressure range, to understand the origin of komatiites, which are these very enigmatic early terrestrial high temperature lavas. Another student, Linda Rowan, who did some of that work, again in the nineties.

That technique was there, but it had only been brought up to the range of pressures you could reach on the single-stage gun. So, one of the things that I wanted to do once I got here was take that technique to the big gun, so we could study the properties of liquids all the way to the bottom of the mantle. That has been the main thread of what I have done with the Shock Wave Lab all these years, is take that idea that came from Stolper and Ahrens, that they developed at relatively low pressure, port it to the big gun, and then explore a wide range of compositions, and eventually hopefully put together a comprehensive enough picture of densities of different silicate liquids at lower mantle conditions that we can solve the problem of, after the Moon-forming impact, when you melted the whole Earth and made a giant magma ocean, how did it evolve, how did it crystallize. The biggest gap in our ability to do that, I think, is the densities of liquids under those conditions. That's really the big thing that I have spent most of my effort on in the Shock Wave Lab, and it grew from this collaboration between Tom and Ed, where what Ed's lab was used for was just to make the glass, to start those experiments.

ZIERLER: I think this is a really important point, as you've alluded. When Tom realized that he would be winding down his career and he asked you essentially to take over, the nature of the request was not that you would serve in a caretaker position until the next Tom Ahrens came along; it's that you were really so closely involved in this research that this was not a caretaker role; you would inherit the lab and this would be central to your entire research agenda.

ASIMOW: Yeah, absolutely. It's such a cool lab, and it's such a unique facility, that it didn't take that much persuasion. If you put a bowl of chocolate out on the table [laughs] somebody's gonna pick it up and eat it.

ZIERLER: Did that mean that you had two labs, or you just had one lab with two components? Did you maintain two separate cohorts of graduate students, or just administratively how did that work during this transition?

ASIMOW: I still have two labs. I have had two labs all this time, one here in Arms, one in the sub-basement of South Mudd. They do operate more or less independently, with some crossover. If there's a project that requires synthesizing something to take over to the Shock Wave Lab and shock, then one person might be working in both labs, but most of the time, what's going on here and what's going on there, in the two labs, is distinct. Students are typically working on one or the other. I haven't actually had that many students that have done standard petrological experiments for their theses. There have been some. The person that crossed the line most often was Jed Mosenfelder. [laughs] I have this pattern of hiring a postdoc and finding them so valuable to my operation—

ZIERLER: They stay.

ASIMOW: —and them being so comfortable here and getting such good work done and not wanting to leave, that they stay. You can only be a postdoc for three years, so after three years, they convert to a staff position. I've done this four times, at least. My first postdoc was Jed Mosenfelder, who had learned the multi-anvil technique at Bayreuth and came to make my multi-anvil lab work, and quickly said, "The way you're doing it is all wrong. I'm going to do it my way." One of the things that Jed could do was synthesize these high-pressure minerals that we could take over to the Shock Wave Lab. The other thing that Jed was interested in was water in minerals, which is kind of the main thing that I did with the static high-pressure lab for several years—taking George's discovery that regular mantle minerals have water in them, and trying to work out how that changes at high pressure, and how do you absolutely calibrate the amount of water that's in those minerals, and that whole endeavor. Jed worked on both those things—the shock wave experiments, and the water in minerals. Jed is first author on a couple of papers where we synthesized high-pressure phases either in my lab or by going back to Bayreuth, where they have a bigger press, and then taking them over to the Shock Wave Lab and blowing them up. That's where the two labs met most closely, was through Luo's thesis and Jed's work on silica and magnesium silicates, on synthesizing high-pressure phrases and then characterizing them by shock.

Controlled Explosions and Safety Precautions

ZIERLER: I wonder if you can talk about how you avoid sleepless nights with safety considerations, given what this lab is and all of the nightmare scenarios that could result in a shot gone wrong.

ASIMOW: Right. It comes down to hiring technical staff that take their lives seriously [laughs] and are deliberate and careful and thoughtful, who understand why the procedure is written the way it is, and who are willing to follow it. I trust my staff to be careful, because they're the ones who are actually in the lab [laughs], firing the experiments. When something goes wrong, something small usually, we sit and we do a review, and we think, "What did we do wrong? What can we do better? How can we update the procedure?" The Shock Wave Lab runs on checklists. There's a checklist for every shot that has all the steps, and if you do them all in the right order, and do them all properly, we can count on the equipment to function the way it's supposed to and detonate when it's supposed to, and not detonate when it's not supposed to. Also, there's no personnel in the Lab when the gun is being fired. We have a bunker with steel blast doors and rotating red lights in the hallway that say, "Don't go in. The lab is not safe." I think we have a successful culture of safety, where we avoid being rushed, we avoid shortcuts, and I feel like I can count on the people that are there, especially the technicians, to both self-monitor their own behavior and to monitor postdocs, students, visitors, that are in the lab, and make sure everybody is following the procedures. That has worked for us, so far. There have been some minor incidents; there have not been any significant injuries or loss of property, and we try to keep it that way.

ZIERLER: Who are the regulatory bodies that monitor the protocols both locally at Caltech, and is there Pasadena, L.A., California, federal oversight also? Who needs to be involved in making sure that all of this goes as well as it does?

ASIMOW: Most locally, Caltech Environmental Health and Safety has authority over all lab safety operations on campus. They need to verify that we have a standard operating procedure and that it is consistent with occupational safety and health rules, and that our chemical hygiene is appropriate and that our radiological hygiene is appropriate. We have x-rays in the lab, so that gets inspected regularly. Gunpowder, smokeless gunpowder, is basically unregulated in the United States, thanks to the Second Amendment, and so for the most part, we can do whatever we want with it. Pasadena Fire Department also has authority to inspect and guarantee safety of operations on campus, and so we have to convince them that our gunpowder is appropriately stored, and that we're not violating the fire code in any way. Beyond that, there's nobody. Except Tom had an explosives license. There are some things that we use high explosives for and not gunpowder. The difference between gunpowder and a high explosive is the rate at which it burns. Gunpowder by design burns slowly enough to launch a bullet rather than blow up your gun. High explosives burn much faster; they are designed to blow up your gun and not accelerate a projectile. They are therefore more dangerous, and they are much more tightly regulated. And so, when there was an explosives license, the Bureau of Alcohol, Tobacco, and Firearms had authority to regulate what we were doing with it, how we were storing it, how we were logging it. I didn't need the explosives license for anything I was doing or planned to do, so after I took over the lab, I terminated the license, which involved a closing inspection by ATF agents who had to come out and verify that our logs added up—the amount we bought and the amount we disposed of added to zero. Actually at that point we found some unpleasant surprises in the storage room, like we moved a box and there was a pipe bomb behind it; literally, a piece of pipe with caps threaded on both ends and two wires sticking out. At that point, nobody remembered what it was, or why it was there, or what it was for. So, Safety was like, "Could you do something with that before the Feds come to inspect?" [laughs]

ZIERLER: [laughs]

ASIMOW: Behind a shield, we opened it up, and there was just a small detonator inside. It was just for a shaped charge experiment. Tom was doing experiments basically in sandboxes, where you would blow up a charge and see what kind of crater you got at the top depending on the shape of the charge. So, yeah, high explosives are tightly regulated for very good reason. We're not doing anything with them. And so if Caltech Safety and Pasadena Fire are happy, I don't need to answer to anybody else.

ZIERLER: Like OSHA, for example, they're not a player?

ASIMOW: Oh, I suppose so, but—

ZIERLER: It doesn't ever rise to that issue?

ASIMOW: Yeah. OSHA doesn't go and inspect workplaces and laboratories. They make regulations, but I don't know who enforces them or how that works.

ZIERLER: For all the time I've spent in the building, I've been waiting to hear or feel a boom, and I haven't. Is that because it's happening off hours? Is that because there's amazing shockproof and soundproofing in there? Is it a combination of the two?

ASIMOW: It's because the explosion is contained inside the gun. We don't move a lot of air, deliberately, outside the gun, and so you don't hear very much. So, yeah, we detonate two kilograms of gunpowder, and from the control room, which is just separated from the lab by a foot of concrete, it sounds like "thud, clunka, clunka, clunka"—after the debris hits the plates hanging in the catch tank. It's not very loud. Jennifer Jackson's lab is one floor up in South Mudd. She has an optics table and a spectrometer, and there was some concern that every time we fired the gun we would knock all of her optics out of alignment. So, we had the seismologists deploy a digital seismometer [laughs], portable seismometer in her lab space when it was being prepared, while we fired the gun.

ZIERLER: [laughs] This is like the most GPS story ever. [laughs]

ASIMOW: Yeah. And my understanding is it registered as a magnitude minus-two earthquake—

ZIERLER: [laughs]

ASIMOW: —which is totally below the noise floor. If you can't stand up to magnitude minus-two earthquakes, you better not [laughs] be in California, because they're happening all the time. So, no, the explosion is contained. The gun can recoil—it's all on rollers—and it's not very loud as long as everything goes right. We did have one incident where the breech plug was not screwed in all the way, and the vent holes were slightly open, and burning gunpowder residue escaped, and that was very loud. That was loud enough that people came down from the floor above to make sure we were still there. And there are six burn marks radially around the breech where that happened.

ZIERLER: A good reminder for safety protocol.

ASIMOW: A good reminder for safety protocol, and good reminder of the importance of comprehensive knowledge transfer from one generation of technicians to the next. Like, the little bit of information that "this is how far you thread in the breech plug"—that was lost, briefly.

ZIERLER: A seeming asymmetry here—the explosion is contained, it's not that loud, it does not create a huge shock—and yet, the explosions are still capable of producing higher temperatures than what you're trying to match to the deep interior of the Earth. Can you square that circle for me?

ASIMOW: The amount of material that reaches the very high pressure and high temperature is very small. It's a centimeter or so in diameter, and a few millimeters thick, and it's only at that condition for 100 nanoseconds or so. So, it's a very small sample of the conditions, a very small and short-lived sample of the deep Earth interior conditions, which is in turn is contained within a rigid steel box.

ZIERLER: Maybe now we should turn to when you decided to come up for tenure.

ASIMOW: I didn't decide. [laughs]

ZIERLER: You were asked.

ASIMOW: The clock expired, right? When you are hired as an assistant professor, you are hired for a four-year term as assistant professor. After three years, there is a review so that they can tell you, with a year's warning, whether you get to stay another three or not. Then there's a tenure decision within seven, which means—actually, within six, because again, if they're going to deny tenure, they give you a year's notice. The tenure clock is such that you need an answer, yes or no, by the time you've been here six years.

ZIERLER: I meant, though, you could have come up earlier if you wanted to?

ASIMOW: Yes, you can ask for acceleration. It's pretty rare. I can remember one case where somebody did. We looked at their case and we said, "You don't want to do that. Come back in a year," and it was all fine. Sometimes the tenure clock gets delayed. Birth or adoption of a child gets you a year. COVID got the current generation of assistant faculty a year. So, my colleague Claire Bucholz across the hall has not come up for tenure yet, but she has been here a long time, because she has had three children and COVID. But I had children before starting as a professor and after getting tenure, but not between, so my clock was just the standard six years. So yes, I came up for tenure not by choice but because it was time.

ZIERLER: Tell me about the tenure process in GPS. Do you give a talk? Is it an opportunity to reflect on all that you've done? Do you look to the future? Just mechanistically, what does that look like?

ASIMOW: Because the whole faculty of the Division vote on tenure cases, regardless of which option they are coming from—and that's a very important part of the culture of the Division; we act as a faculty as a whole on all these hiring and tenure, promotion decisions. But, faculty in options that I'm not in might not know very much about me or what I do, so the best way to give them an opportunity to do something other than read the file to form a personal opinion, if they haven't had a chance to meet me, is for me to give a division seminar. That is one of the things we use the division seminar for, is sometime in the last year before coming up for tenure, an associate professor will typically give a division seminar. Then, a committee is formed. The tenure review committee is related to, and usually closely overlapping in membership with, our tracking committee. Every assistant professor gets a tracking committee that meets with them at least once a year through their junior faculty appointment, just to track and give advice and know what's going on, and so there hopefully aren't any surprises. About six months before an answer is needed, the chairman asks somebody to chair a tenure review committee. It's typically the person who has been chairing the tracking committee. You get a committee together, they meet and they plan, and figure out who to ask for letters, and they give the chairman a fairly long list of people, longer than ideally is needed. The chairman sends out some very large number of letter requests. We usually have like ten letters or something in our tenure packages, both from people who know personally and have worked with the candidate, as well as outside experts in the field, to get a sense of their reputation beyond their immediate social circle.

The tenure committee also commits to really engaging with the science and reading a bunch of the papers and discussing them and understanding not just what the letter writers tell them, but for themselves, what is the significance of the work. The candidate turns in a couple of documents—a summary of their own assessment of their research to guide what they think is important and which papers they would really like the committee to focus on, as well as a forward-looking plan for, if you get tenure, what are you going to do with the rest of your life. And, a teaching statement—"This is what I've been teaching, this is how I've been teaching, this is what I think I'm good at and what I think I'm bad at." We now require diversity statements for assistant professor hires. I don't know that we've added that as a requirement to a tenure case, for you to say what you've done for diversity, equity, and inclusion in the Division, but I suspect, if we haven't, we soon will, just because we're trying to build that in at every stage of our process, to make sure that we're aware of diversity concerns throughout our academic work cycle.

ZIERLER: The teaching statement, by necessity, must be somewhat blunted because there are not many undergraduates closely involved in GPS?

ASIMOW: We also have graduate students, and we teach them classes. We make them take a fairly large number of classes in their first two years. So, yeah, we all teach. We don't teach a lot of people in most of our classes, but nevertheless, we are deeply concerned that we are doing it well, and not wasting people's time or conforming to stereotypes of people who know how to do research but don't know how to teach. I think the GPS Division values the quality of its teaching. Even though we're not teaching very many people, we try hard to teach them well. So, ideally, you do a big push to get a bunch of papers finished, and ideally get a couple of students through to their degree and get them out the door, and accomplish a body of work that feels like, "Okay, this is what I can do, this is a good demonstration of the fact that I have a good nose for problems, I know how to formulate a plan to solve those problems, I am efficient at getting from the idea to the proposal to the research to the paper, and getting it out the door, I am reasonably good at mentoring students and postdocs and making sure that they succeed and go on to good places in their careers." And, "This is a demonstration of what I can do, and you just have to trust that I'm going to keep doing it." That's what a good tenure package says.

Reducing all that to one sentence, the rule, the guideline—and as far as I know, Ed Stolper formulated it this way and promulgated it—the criterion for getting tenure at Caltech is you must change the way people think about an important problem in science. Simple as that. We don't count papers. We don't—"Oh, you have to have five papers or you're not going to get tenure." It's not like that. One supremely influential masterpiece of a paper could be enough; a hundred lousy papers would not be enough. We have the time and deliberation and consideration to be qualitative about our judgments, rather than at least my sense of certainly in other countries and at some large university systems that have had to streamline everything to a process that can be turned—the crank can be turned quickly—it seems like it's much more numerical: "You need this many papers," and nobody has time to read them and see whether they're any good.

ZIERLER: In articulating your accomplishments, the shock wave work, you were full enough in on that, that this was part of the messaging of what you had accomplished, or that was more provisional?

ASIMOW: It was early. It took a while to really bring a lot of the threads of what was going on in the Shock Wave Lab to fruition. The Luo papers on silica—those were like 2002 and 2004—and 2003—those were out in time. But that was joint work with Tom. There were no first-author papers there, for me. The computational stuff that I was doing with the MELTS model and growing out of bringing the MELTS model into contact with real rocks that happened while I was a postdoc, that was more mature and led to papers during my assistant professorship that were much more widely noticed and more influential, in igneous petrology. A paper on how you account for the behavior of water in the mantle. The paper basically putting together in full form the work that I had started for my thesis. Those were first author papers; those were all me and all mine. At this point, as much as possible, I was not collaborating with Ed, and Ed was not an author on some of those papers, just to establish my independence as the expert on how you do this kind of calculation and what it means.

ZIERLER: This is to get to the larger concern for junior faculty— don't overly collaborate because you want to demonstrate that you can stand on your own two feet.

ASIMOW: Yes. The tenure case rested primarily on demonstrated accomplishment in thermodynamic modeling of upper mantle melting and in preliminary demonstrated accomplishment in making the two labs work and getting things done with them. The most influential paper that I've written—influential papers—to come out of the Shock Wave Lab were too late for the tenure case. They were like 2007, 2009. 2010 papers. But that was okay.

ZIERLER: It was also not the basis upon which you were hired here. The whole shock wave could have not existed—

ASIMOW: Exactly.

ZIERLER: —and you had a corpus of work that you were prepared to make the case for.

ASIMOW: True.

ZIERLER: It was sort of like that was all value added, to some degree.

ASIMOW: Yeah. Nobody has, and nobody would, say anything explicit about what my tenure review process was like, and that's how it should be. But from tea leaves and hints, I sort of get the sense that, as with my hiring, it was still a little bit about promise, people's faith that I would do great things and continue at a steady pace to do great things for my whole career, rather than as much about accomplishment, what had been done at that point, as maybe would have been ideal as maybe people would have liked to see.

ZIERLER: I'll ask a really hard question. You're well prepared to answer it because you didn't want to go to Harvard precisely on this. If in some alternate universe you extracted your work here and you came up for tenure at Harvard, would you have been one of the 15% that crossed the Rubicon? What do you think?

ASIMOW: No, probably not. Yeah—probably not.

ZIERLER: Because Caltech values the long view in nurturing an academic career, they could see where it's going? They could be—generous isn't the right word, but they can have a longer view, essentially?

ASIMOW: I think so, yeah. Here, we view it as a personal failing if one of our assistant professors doesn't thrive, and I don't think other institutions feel that way.

ZIERLER: To go back to Ed Stolper's pithy statement about just paradigm-shifting, do you feel like you had done that circa 2004, 2005? Had you changed the way people thought about the science?

ASIMOW: Yes.

ZIERLER: If that's the case, and Ed's a Harvard product himself, just to push you a little bit, maybe you would have gotten tenure at Harvard.

ASIMOW: Okay!

ZIERLER: Because you change the field; you don't change the institution.

ASIMOW: I don't know if that's Harvard standard, though. That's Caltech's standard.

ZIERLER: Ah! [laughs] It's not enough for Harvard to change the way people think about science! [laughs] That's interesting. Did you give the division seminar?

ASIMOW: I don't remember. Probably yes. I think I've given one.

ZIERLER: Clearly it wasn't a big deal, then. I mean, if it doesn't loom in your memory.

ASIMOW: Yeah. There are records. [laughs]

ZIERLER: The good news is delivered casually? You see Ed in the hall and he says "Congratulations"? Or what is it like?

ASIMOW: [laughs] Yeah, basically. But then there's a suitable celebration. They arrange a dinner for you and your spouse at the Athenaeum and mark the occasion. The process—the committee asks the chairman to go out for letters, they get the letters, they read the papers, they write a report, the report goes to the full senior GPS faculty, the full GPS faculty votes, that then goes under the sort of aegis of the chairman to the IACC, where all the division chairs and the provost and the president vote on the tenure cases brought to them by the chair from each division. Then it goes to the trustees, and once the trustee meeting has happened and the news comes back to the chair that it's official, then the chair will come and say, "Okay. Congratulations. You have been promoted." I'm sure this is one of the better moments in the life of a division chair, is being able to deliver that news. [laughs] It's one of the important responsibilities of the division chair is to hopefully get a strong case with a unanimous consensus from their faculty and then even with that, being able to bring it to the IACC and explain, to people from all different fields, why this work is important and why this person ought to be at Caltech for their whole career. I have heard Fiona Harrison, the chair of PMA, complain that one of the things she has to do as chair of PMA is bring forward tenure cases for pure mathematicians—

ZIERLER: And who knows what they do!

ASIMOW: [laughs] Basically cannot be explained [laughs] to anybody else!

ZIERLER: [laughs] That's funny. Yeah, that's really not an issue in GPS. The faculty are closely aligned, where you really can get deep into understanding what your colleagues are doing.

ASIMOW: Yeah. I also think it's not that hard to explain to any physicist or chemist or engineer or biologist what it is that we do. I go to commencement every year, because I play in the brass, and one of the forms of entertainment at the commencement ceremony is reading all the PhD thesis titles. They're all in there. I develop a sense of the culture of how you write a thesis title, and as far as I can tell, thesis titles in Earth sciences are written to be understood [laughs], and thesis titles in other sciences are not [laughs].

ZIERLER: [laughs] You mean understood by the layman.

ASIMOW: Yes.

ZIERLER: Anybody can figure out what you're talking about.

ASIMOW: Right.

ZIERLER: This is a purely administrative, Institute-wide question, but I think you're one of the last generation to get tenure with the associate title before Caltech did away with that and went straight from assistant to full. What are your thoughts, benefits, and pitfalls, of either system?

ASIMOW: It was clearly a step forward to save ourselves the trouble and our letter writers the trouble of having that extra step of promotion to associate—or rather of promotion from associate with tenure to full professor. It comes a few years after tenure; your letter writers are like, "Why are you asking me again?" And, it was kind of subject to abuse by—my sense—by the chair of a division. That someone has tenure, they're an associate professor; if you favor them, you bring them up for promotion, and if you don't, you let them languish. Because there wasn't really as formal a clock of when you're supposed to be brought up for promotion to full professor. I don't think the chair should need that extra stick to motivate tenured associate professors to continue to work hard and produce, so that they can be promoted to full professor.

ZIERLER: Do you think that that's unique to Caltech, because if the expectation here is that faculty are world-leading researchers, is that the kind of scholar, is that the kind of personality, that doesn't need that extra bit of motivation to get promoted from associate to full, where that might be the case at a state school, for example?

ASIMOW: We have a much better motivation, which involves much less administrative overhead, which is the awarding of chaired, endowed professorships. There aren't enough chairs to go around, and so, there are a lot of professors that are just "professor." Getting an endowed professorship is actually a significant item of value that is more than just a badge that your title has changed from associate professor to professor. The deal is—maybe other chairs are different—the deal with the McMillan Chair is, when I was just "professor," if I write an external grant proposal and it includes some of my salary—which I don't need to do; I get a 12-month salary from Caltech, and I get paid the same amount whether I bring in my salary or not—if I bring in some of my salary, as an assistant professor I would then get 25% of that back in a green money discretionary account to spend on whatever I want. Discretionary money is great. Awesome. It's the most valuable resource. You don't have to justify in advance what you're going to spend it on; you just have an idea, or a student comes to you, and you say, "Okay, sure, I have some money for that." It's the best. But 25%—what you actually have to do to get that quarter is you need to bring in a dollar of your salary on a full overhead-bearing grant, plus benefits, so it actually costs about $1.85 or so to get that quarter, with the result that when the Institute said to me that I could not charge laundry for my technicians' lab coats to any federal grant because they were working on more than one grant, and they didn't think I could prove which grant was getting their laundry dirty—

ZIERLER: [laughs]

ASIMOW: —they said, "No, the only money you can spend on lab coat laundry is your discretionary account," and I said, "You just put a 750% overhead rate on laundry, and that's insane." I actually picked that fight with the Sponsored Research Office and I won it. But once you get a chair, now because your salary is being paid from the endowment and not from the general budget, Caltech can be more generous. With a chair, if I write a dollar of my salary into a research grant, I get 90% of it, in my discretionary account. I can bank it. I can save it. I can even, when it's enough, get a little carved-out share of the endowment that is just mine, and gain returns equivalent to the return on the whole endowment. That's the incentive to get a chair, and that's much more real and much more valuable than whether you're an associate professor or a professor.

ZIERLER: That's not a badge; that's allowing you to do better science more easily.

ASIMOW: Yes. You still have to go out and raise your salary [laughs], but they make it very much worth your while to do so.

ZIERLER: In our next conversation, we'll talk about some of the administrative responsibilities and interests that you can pursue with tenure—diversity, things like that. Last topic for today to touch on is I'm very interested as I mentioned in how professors respond to both the freedom and the responsibility of having tenure, what that means in terms of branching out, being more adventurous, doing things that are not in your sort of very hyper-defined wheelhouse as a junior faculty member. Is that to say, in the way that the shock wave work was sort of transitional, this was a way that you can articulate, "I'm in the middle of this now, and great things will happen if I get tenure to continue on that"? Where would you put in the narrative what would eventually come out of the fieldwork, rock collecting in places like Greece and Africa? Does that only get articulated, do you only start to establish that, once you take a breather, you have tenure, you can think about next steps? Or is that sort of like always in the background and you're thinking to yourself, "If and when I get tenure, I'm going for this"? What's the timing of that as an intellectual trajectory?

ASIMOW: No. I was busy with computations and experiments in two different labs, and I had all the work that I needed to keep me occupied with things on the computer or in the lab, and I didn't really think about conceiving a field program or going to the field while I was an assistant professor. It wasn't by choice; it wasn't like, "Okay, I don't have time, and it's not going to yield a return quickly enough to be worth my while." I wasn't making those calculations. It just, at that time, that part of my interest, that way of doing science, it was just fallow. It was just sitting there. It wasn't yelling very loud, and it wasn't an itch that I needed to scratch.

ZIERLER: Even though—and this is a very funny point—you got into this business because you loved nature, you loved going out into the field. Was that ever bothersome to you, as an assistant faculty member, that you weren't out there, or you weren't traversing the Earth doing all of this amazing collecting? Or did you have the long game, that eventually you'd get there?

ASIMOW: I wasn't thinking about it. Later—looking back—like sitting on a rock looking out over the icebergs on Baffin Island, I'm like, "Oh, yeah." [laughs] It all came rushing back to me, that that was what I had originally had in mind when I envisioned this field. But, no, for a few years at least, it just sat there. It wasn't crying. I wasn't missing it. I wasn't consciously or strategically choosing not to go to the field. It just wasn't what I was doing.

ZIERLER: You had more than enough to keep you busy, didn't even have time to think about it, maybe.

ASIMOW: Yeah. And so most of the field-related projects that I have gotten involved in more recently have arisen through collaboration. Geologists who have a field area that interests them or have done the fieldwork and picked up rocks and need help processing them, analyzing them, modeling them, interpreting them, have come to me because of my modeling expertise, or because of my access to analytical resources. For many years, I was content to say, "Okay, send me the rocks and I will work with you on them." Again, only recently, my answer has been, "I need to see the field area. Let's go." Hopefully I will be able to do more in that mode going forward. So, yes, what tenure really gives you is time. I can conceive a project that I know is going to take ten years to lead to a paper, and that's fine. You can't do that as an assistant professor. Assuming you are thinking strategically and feeling the pressure and trying to optimize what you do to get tenure, you have to think, "What can I do that will show results within six years from when the clock starts?" Five and a half really, because your letter writers have to know about it. That limits the range of things that you can conceive of, and the range of things you can do.

There are projects that are good for a graduate student because they can be accomplished in the time span of one PhD. There are projects that are good for postdocs because they can be accomplished in a year or two. There are projects that are good for an assistant professor, which conveniently is roughly also the same time span as one PhD, so you can get a student out the door and show both that you can mentor and that you can conceive and execute a project and publish it. Then there are things that just take time, either because you have to build a whole new apparatus, or you're going to have to go to the same field repeatedly to collect enough data, or in my case, just because I'm distracted by doing so many things that each thing moves along at a slow pace. Once you have tenure, that's fine. You have time. Ideally, there's enough balls in the air that some of them are being caught at any given time, but you can throw one really high and wait for it to come down, and that's okay. This is a good thing, because a lot of blue-sky projects, a lot of original interesting work, from the idea to the final execution, is going to take time. We want that kind of work to get done. So that, to me, is the reason to have tenure.

The original motivation for tenure, academic freedom, is so the university can't tell you what you should be working on and what you should say and regulate your speech and your behavior. But in science, most of us are not saying controversial things that are going to make anybody want to fire us. What we're doing is either producing results that are obviously interesting now, or maybe doing things that may lead to interesting results someday. Cultivating an environment where you can do that kind of work that may lead to an interesting result someday, that's where the good stuff comes from, and so that's why it makes sense even in the context of science and engineering, where academic freedom isn't really the issue—in a way, it is; it's academic freedom not to do controversial things but to do things that seem dumb to everyone else.

ZIERLER: You explained quite well I think that you had too much going on to have time to miss the fieldwork during your junior professor days. Did you feel there were missing pieces of the puzzle, that if you survey all of your work—the deep mantle, with shock wave—not going out into the field, was that a detracting point for your research, not going out there yourself? Or did you see this really as a new line of inquiry, as a new branch in your research agenda?

ASIMOW: More the latter. A lot of the experimental and computational work is sufficiently generalized that its impact comes from being able to apply it to any field area, rather than applying it to a particular field area. You can't do enough fieldwork to [laughs] generalize by doing it all yourself. You need to depend on the accumulated fieldwork of many generations of geologists who have collected data from lots of places so that there is some general target to apply your model to. By the time I was working on the origin of mid-ocean ridge basalts, people had been dredging mid-ocean ridge basalts for 40 years and compiling those data and looking at the systematics. I wouldn't have made that big an impact by going and dredging my own. I did that, in 2004, and I never actually wrote a paper about anything that came out of that cruise. I'm coauthor on a couple things. I did have one idea that emerged from the work on that cruise that I gave a meeting abstract about, but I was missing a piece, and so I didn't finish the paper. Ten years went by, and then I was sent a paper to review that said exactly what I was going to say, with the missing piece. It was a collaboration between a seismologist and a petrologist. But this has led to one of my dicta, which is that "The statute of limitations on a good idea is ten years."

ZIERLER: [laughs]

ASIMOW: If you don't write it, someone else will write it for you. [laughs] It was an interesting review to write, because my review was basically, "Yeah. I was gonna say that." [laughs]

ZIERLER: There must be some satisfaction there, even if it's not your idea.

ASIMOW: Yes, especially because the first author had been an undergrad here, and a SURF student in Ed's group.

ZIERLER: In our next talk, it's a big planet, we're going to pick up on where you decide to go. There's lots of choices you have—what's most important, what's most interesting. The last question for today, just to close out—it's very sad I never got to meet Tom Ahrens—what's his legacy? For people that should know but didn't know his contributions, what would you want to tell them?

ASIMOW: The idea that dynamic compression, which is to say shock waves, form an essential complement to the other methods that we have of understanding the properties of rocks and minerals and planets at high pressure—that really is something that Tom developed and cultivated and taught a generation of students to appreciate. He was really the main link between the world of shock wave research, which mostly takes place at national labs, and mostly takes place in an engineering or military context, and the world of geophysics and planetary science. Tom was the one that brought them together.

There was a—there is, still—a biannual meeting of a branch of the American Physical Society called Shock Compression of Condensed Matter, which always has a session on geophysics and planetary science, and it's pretty much Tom and people that worked with Tom that populate that whole session of that meeting that represents this intersection between this area of physics and engineering and this area of Earth science. Tom made the bridge, built it out over a full career, and left it stable enough that even without him, the bridge is still there, and there is still an appreciation of what this range of techniques can do, and why it's complementary to what the much larger communities on either side of the bridge are doing. That's one legacy is the intellectual link between these disparate fields of science. Another is the large number of people that he influenced and trained who have gone out to leadership positions in mineral physics, in petrology, in Earth and planetary science. The other is the lab itself. It's a really good facility. It has been worthwhile and not that difficult to keep it running for 16 years now, beyond Tom's retirement, because it was a well-built lab that was an ambitious enough thing to do that not that many other universities have attempted it. Also, he left me with a running start, with not only the equipment but with very dedicated and experienced technicians that got me going until I knew enough that I could hire the next technician, when the people that had worked with Tom retired. Everything has now turned over. There's nobody in the lab that worked with Tom except me. But I never would have had the wherewithal to build such a lab or understand how to do it right and get it running, and Tom knew that. So, he gave me a good start.

ZIERLER: It was a turnkey operation that allowed you to take it to the next level for you.

ASIMOW: Yeah. Well put.

ZIERLER: On that note, we'll pick up next time on, where on Earth does Professor Asimow go for his field research?

ASIMOW: [laughs] Okay!

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Thursday, June 1st, 2023. It is great to be back with Professor Paul Asimow. Paul, once again, thanks for joining me.

ASIMOW: You're welcome.

ZIERLER: Today, what I want to do is first ask some overall questions as they relate to your decision post-tenure to move into field research. Maybe to set the stage, we were talking last time that you were so focused on the laboratory side of things you weren't even thinking about the pull of field research. It was only when you got out were you reminded why you got into this in the first place. But more substantively, intellectually, in making that move into field research, were there parts of your laboratory research agenda that needed to be completed in the field? Was that two sides of a proverbial coin, where there's an overall research agenda, and the laboratory research really was the precursor or the foundation of what would come next, or is it really separate tracks, different endeavors, different pursuits?

ASIMOW: The laboratory stuff and the fieldwork are very separate pursuits. Most of the lab work that I'm doing is related to the very deep Earth, the very early Earth, things that are not easily accessible in the rock record in the field at the surface of the Earth. On the other hand, the computational work, which is the other component of what I was doing, other than being out in the field, I was creating tools and putting them out there for other people to use, both to understand general processes, but also to look at their particular rocks from some particular place and see if they could understand what processes created those rocks with the help of the modeling tools that I was creating. But I wasn't really using the models very much myself; I was putting them out there. So there is a thread there, in that frequently when I go and get some rocks or somebody sends me some rocks and I turn them into data, I will then take my modeling tools that I'm fairly expert at using, and apply them. I think it's a more interesting project for me at least if I can do that. So, there is a connection between the computational and theory work and the software development and the applications to particular places.

But in terms of why this kind of did wait or had to wait until a little later in my career, at least for me, it's relatively easy to make a broad impact by creating a tool and putting it out there for everybody to use. That attracts lots of citations and everybody notices, and you have an impact on the whole field. Or, by doing a well-chosen experiment to illustrate a general process or to measure some physical property of materials that you can find everywhere you go. It's much harder to know that a given field project is going to have any impact beyond the immediate field area. Most don't. Most of the time, you either go to someplace and it turns out to be typical, and so it's another example of a phenomenon that people already pretty well understood, or, it's such a freakishly unique place that it's only important unto itself [laughs] and doesn't tell you about anyplace else. The relative handful of regional studies that discover something new and general, that it's going to change the way people think about other places, those are rare, and they are kind of serendipitous, usually. Usually it's because you're lucky. Unless you're really smart and intentional, you don't really know when you go out on a mission of discovery whether you're going to discover anything that is going to be interesting enough to have an impact. And so, it's a little risky as a thing for an early career researcher to do. I could say that I had the foresight to understand that [laughs]; I'm not sure I did. But looking back, I think there's some logic to that.

Calculating Risk for Fruitful Fieldwork

ZIERLER: Is it risky in a generational sense? In other words, because you were able to make an impact on the field by building tools and computation—these technologies are obviously not available in previous generations—are you saying that there's a certain risk there, relative to your generation because of the availability of these tools, and it would be foolhardy not to lean into that aspect of it?

ASIMOW: Not exactly. In each generation, it is true that many of the most influential scientists are not the ones doing the bulk of the work but the ones that are facilitating everybody else being able to do the bulk of the work. The genomics revolution involved lots of people sequencing a lot of genetic data; it was all facilitated by the people that developed the gene sequencing machines, who then didn't have to go sequence all the data themselves. They put the tool out there for everybody. In my generation, thermodynamic modeling tools reached the point of being useful for interpreting complex natural rock suites, so it was a very strategic thing to do to glom onto the thermodynamic modeling project and do what I could to make it accessible and accurate and useful to people.

But in earlier generations, it was drawing simplified phase diagrams that could be used to interpret complex rocks up to a point. In earlier generations than that, it was some of the very early experimental work that showed just the basic way that things work, that set up paradigms in which people could then interpret their particular data. The mode in which I am working now, frequently, is some collaborator goes to a field region because it's accessible to them, or because they have money, or because they think there might be some interesting economic resource there, they pick up a bunch of rocks, they send them to me, I analyze them, we look at the data, and I either just write a descriptive paper that says, "This is what we found here," or say, "Oh, okay, I can model this process in a way that nobody has modeled before," come up with some rules and some guidelines and some intuition that somebody might be able to apply to another similar region somewhere else. I prefer it if I find a nugget in the paper that I can build into something like that. I try to do that in all of the papers, but sometimes there just isn't anything, and I don't know in advance which ones are going to be which.

ZIERLER: If there was a bit of hedge in your answer in saying that these are largely separate pursuits—the fieldwork and the lab work and the computational route—if there is any overlap, is there an example of something feeling provisional to you in the laboratory or on the computer, for which you gotta get out on the field and it's going to complete the story?

ASIMOW: In a sense, all of it. As an Earth scientist, as a geologist, I firmly believe that the truth is there [laughs] on the ground, and in the ground, to be picked up. That's where the problems come from, the puzzles—from observation, and then trying to explain the observations. Then you come back into the laboratory or into the computer or onto the back of an envelope and come up with some framework for interpreting those observations. Then like all hypotheses, they need to be further tested, to see if you can reject them, and the way you test them further is go back out to the field and apply them to new places.

ZIERLER: Is that to say that toggling the interplay between experiment and theory for the first part of your faculty career was to some degree incomplete, absent the fieldwork?

ASIMOW: Yeah. I occasionally said aloud to people, "I feel like a parasite." Like, "I'm analyzing other people's data and I'm not generating my own." I felt that. That's one of the reasons that I went to Lamont as a postdoc to get out to sea, to get some real rocks and some experience dealing with them. Many hours ago in this interview series, I mentioned Dan McKenzie, a Cambridge professor, influential geophysicist who later became an annoying geochemist, as one of my inspirations, one of my [laughs] nemeses, one of the people that I set much of my work either in opposition to or following from. He explicitly said this. Before mounting a series of campaigns to go and do fieldwork in Iceland, he said, "When the theory reaches a dead end, it is time to go back to the field." I don't know that the theory has reached a dead end, that I have a comprehensive enough closed-form view of what you can do with theory, but that's what Dan felt—that he had reached the end of what he could do with the available data and needed to go out and get more data.

ZIERLER: We talked in some detail last time about what you articulated in the tenure process, your contributions. What about in terms of articulating a forward-looking plan? During that process, is this where you sort of put the word out that if you are to get tenure, if you stay, this is where you're headed next? Do your colleagues have an awareness that the process is complete, and now it's time to get out there? Or is it more gradual even to yourself perhaps?

ASIMOW: The process wasn't complete, at the time when I came up for tenure. The shock wave experiments hadn't really reached fruition; the most significant paper that I feel that I wrote came out in 2010, and I was up for tenure in 2005, 2004. I guess the main computational tools were in place at that point and the main theoretical ideas that I developed from them. It was really the shock wave experiments that I hadn't been doing it long enough for it really to show results at that point. I didn't really make this shift into doing a lot of collaboration with a lot of field geologists, much less any field expeditions of my own, until more like 2014. I'm sure I did write a forward-looking plan in my tenure package for what I planned to do, and I'm sure what it said is, "I'm going to do a bunch more of these shock wave experiments and get to the point where I have something comprehensive and new and interesting to say about the densities of silicate melts in the lower mantle." Because that's what I was doing. My colleagues accepted that that was apparently where I was going. That's the thing about tenure, is whatever you say in your tenure statement about what you're going to do is totally non-binding. [laughs] You do either whatever short-term or long-term research you feel like doing and can get supported.

ZIERLER: You articulate a plan and everybody understands that it's subject to any number of changes.

ASIMOW: Yeah.

ZIERLER: The chronology is, you don't really start thinking about field geology, field research, until 2013, 2014?

ASIMOW: Yeah, 2014 is when Mokhles Azer, who is a geologist from the National Research Center in Cairo, in Egypt, sent me an email saying, "I have funding from the U.S. Agency for International Development for a postdoctoral mission somewhere. I'd like to come spend it at Caltech." My response was basically, "You have your own money. That sounds good. Let's do it." He came for a few months in 2016, I think. At the time, his spoken English was really rudimentary, and we could not communicate in person. We had done fine setting up the trip and planning for what we were going to do, by email, and he got here, and in person it was not [laughs] constructive. Instead of trying to really work together on ideas at that point, I said, "Let's just get some data. Let's operate the machines, which we can do. You'll take the data home, write a first draft of the paper, and we'll communicate in writing until the paper is done. Let's make that our mode of operation." That has worked great. We have 30 papers now, seven years later, about various aspects of the geology of Egypt and Saudi Arabia. Wasn't anything I ever planned to do. It's a very interesting place. It's a very good example of how continental crust was built, roundabout 600 or 700 million years ago. It has been a very fruitful collaboration, where he's on the ground getting the rocks, I have the tools to analyze the rocks, he's efficient enough to assemble all the data and put together a first draft of the paper, I'm a good enough writer in English that I can polish the paper and make it presentable. And, when there's something I can sink my teeth into in the data to add some modeling weight and make it a more general, more influential paper, I add that, and it goes out the door. So, I just stumbled into writing 30 papers about Egypt, because of Camp David. Egyptian scientists still get more money than others from the U.S. Agency for International Development, because the U.S.—

ZIERLER: Oh, wow.

ASIMOW: —has been sending money there to reward Anwar Sadat for making peace with Israel 35 years ago, 45 years ago. [laughs]

ZIERLER: Wow. That's nice to know it doesn't all go to tanks.

ASIMOW: [laughs] I think not! That's how the whole Egypt thing happened. I answered a cold call, basically. Someone called me up and said, "Can I come visit?" and I said, "Sure!" This has worked a few times. Sometimes it's more like a student writes to me, early maybe in their PhD career somewhere abroad, for help with modeling or for help with analysis. If they have an interesting problem and they seem like they have it together, I might say yes. I've done that a few times, and I've ended up with some very lengthy relationships. So, I have also a bunch of papers about the geology of Greece. Then, that Greek student that I started working with moved, partly through a postdoc that I helped him get, into working on meteorites, and so now we have lots of collaborations about meteorites as well as rocks from Greece, and he has been a fruitful collaborator over the years. I have this postdoc right now from Cameroon, where likewise, he wrote to me when he was a PhD student in Cameroon for help with this project. That also has proven to be fruitful, and I spun it into an opportunity to actually get out and go to Africa and pick up some rocks.

ZIERLER: I want to return to what sounds to me like a Catch-22 that you've identified in field geology. It's either that a finding is so hyper-specific that it doesn't really tell us much more than what we learn at that particular site, or, it's sort of more of the same; it's typical. Is that to say then that the holy grail of field geology is extrapolatability, finding something that is both truly unique and tells us something more about the immediate finding? Is that the goal?

ASIMOW: Yeah. The goal, I would say—in my mind, since the advent of plate tectonics as a unifying, physically based theory for how the Earth works as a dynamical system, the holy grail is finding the most archetypal example of some general phenomenon, where it's well preserved, it's well exposed, you can see all the relations, you can work out how things are connected in this place, and make a plausible case that all these other examples are more fragmentary or more metamorphosed or not as complete, but what you learned by looking at the complete example helps you to understand and fill in the gaps in those other places. That's the best place to go, is something that is an example of a very widespread phenomenon through space and time, and it's the best such place because you can get the clearest picture of it.

ZIERLER: But to clarify, there's no such thing as a failed field geology mission, right? There is what to learn—

ASIMOW: Oh, sure there is! [laughs] There are some quite spectacular failures! [laughs]

ZIERLER: Assuming that you find samples and you can analyze them—

ASIMOW: My colleague Mike Lamb almost had such a failed experience. They had five weeks in Alaska and they spent four of them in COVID isolation. [laughs]

ZIERLER: I mean, not barring administrative, epidemiological—the other stuff.

ASIMOW: [laughs]

ZIERLER: Just when it's you and the rocks, and you find rocks, and you analyze them. What I meant was, if you get to that point, if it's mission accomplished in terms of getting to the rocks and analyzing the rocks, there is value in assessing if this is typical, or if it's unique to this area. That's what I mean.

ASIMOW: Right. One of the harshest responses that you can get from a journal editor is, "This would be more appropriate for a regional journal." Meaning, "Why would anybody who's not working on this area want to read this paper?"

ZIERLER: It's a big planet, right? What are the intuitions that you can rely on—resources are tight, time is tight, you want to spend your resources in the area that is likeliest to produce that holy grail. How do you make those calls? How do you increase those chances of finding something noteworthy?

ASIMOW: I don't know. I'm not sure I have that skill, what we call a nose for good problems, which is why I've kind of let myself stumble from place to place according to potential collaborators who brought forward things that they want to work on. I've never sat down really from scratch and said, "Okay, if I could go anywhere, where would I go?" One such place that I would go would be Baffin Island. I went there for a different reason and kind of realized halfway through the process of planning it that, oh, this is really a good place to go for igneous petrology and not just for crater hunting. That was serendipitous. In general, unless you're just completely fishing, there has to be some reconnaissance information. Somebody has been there before and seen some promising things, but either didn't have the time to focus at the scale where you can really unpack a problem, or, didn't have the analytical tools because they were working there a long time ago, or didn't sample it as well as they might, or didn't run all the analyses that you might run, or didn't have the capability to really attack the problem. So, reconnaissance scale field geology is extremely useful for somebody going out and identifying in general what's out there. At one level, it makes it the basic job to fix the inadequate map that is available, but if you didn't have the inadequate map, you wouldn't know that it was worth going there to fix it.

ZIERLER: When you say you don't have a good nose for these things, is that a humble way of saying that nobody really does? Or can you point to like, "Bob Sharp; he knew where to go!"?

ASIMOW: [laughs]

ZIERLER: How does that work?

ASIMOW: Some people do choose with intentionality places to go that are going to pay off and are going to be influential. Absolutely. There is a professor at UC Santa Barbara named Brad Hacker, and another petrologist that I know, Peter Kelemen, who is at Lamont now, although he was at Woods Hole when I was at Lamont; Peter said Brad Hacker is the world's best field geologist. At the time I didn't quite know what he meant, and how you could make that call, but I think it's exactly that; I think it's that he knows where to go. Lots of people know what to do once they get there, but Brad has several times identified field areas and mounted campaigns there that turn out to be extremely influential, for understanding the structure of island arcs all the way from top to bottom because there's a well-preserved tilted section; for understanding very high-temperature metamorphism by going to Madagascar. So, yes, I think there are people who have done it enough times that it can't be luck.

ZIERLER: It can't be luck. So, there's more there.

ASIMOW: Well, it can be.

ZIERLER: No, no, but in terms of this is not just him having a good run at the blackjack table. There need to be some underlying skills and perspective that he's applying to achieve that consistent level of success.

ASIMOW: I think so.

ZIERLER: What are they? What does he know? [laughs]

ASIMOW: I don't know. [laughs] Presumably, it's—reading the literature to know what has been observed by the reconnaissance studies. Picking up key phrases like "very fresh rocks" or "very complete exposure" or "very high-pressure section." Also sensing when the story is not finished, when the data that are presented can't be the entire set of observations that could be made in the place.

ZIERLER: Given how unsure these things can turn out, when you have graduate students who want to go do field work, what's the moral consideration in terms of setting their expectations, giving them advice where you don't know the answer yourself? How do you work through that?
ASIMOW: I haven't. Because grad students don't come to me and say [laughs] "I want to do a field project." It's not what I'm known for. Graduate students come to me because they want to do experiments, or they want to do calculations, or the things that I was doing earlier in my career for which I'm known well enough that it attracts prospective students. Given the short time span of student projects and student residency, I would rather have them join a project that is already some distance along, so that I know that it's going somewhere. I had a graduate student work on the Baffin Island rocks, but she joined the project after the rocks were already here. The student who went along on the expedition and did the paleomag sampling as a side project kind of knew that was going to work, and it was just a side project. It wasn't like I was tying his whole thesis to this project. I have another student who is working on the Egypt rocks now, but I had already been working on Egypt rocks for a long time, and I had a sense of what were the important problems that needed solving. Other than that—I'm looking at all of the theses on my shelf—none of my other graduate students have done anything really field-related.

ZIERLER: Is this to say at the end of the day that it's generally not advisable for junior faculty members to begin their career in the field? Is that basically where the discipline is now?

ASIMOW: That's a really interesting question. We hired Claire Bucholz because she is field-capable, because we needed someone to teach field geology, and because we believe that field geology is important, and because she demonstrated, as some of the several things she demonstrated before we hired her, that she could do it and produce results. But she also was doing modeling exercises and collaborating with experimentalists. That comes back to something that actually Jason Saleeby said that I remember. Jason, who recently passed away, was a professor here from the 1970s until the 2000-somethings, a field geologist, and an isotope geochemist. He said, "I don't think you can get the respect of the Caltech GPS Division, of your colleagues, if you're just a field geologist. You have to be field geology plus." Meaning, he felt the need to operate an isotope geochemistry lab here for doing geochronology and radiogenic isotope geochemistry and not just do the field geology and collaborate with someone else who could make those measurements.

ZIERLER: The sentiment is that you're basically just a stamp collector.

ASIMOW: I don't know if this sentiment actually exists, or this is just Jason's opinion. I think there's a diversity of views amongst the faculty. Some of us love fieldwork. We think it's cool. We think it's important that we have a field program for training students. We've done enough fieldwork that we know how difficult it is, the intellectual challenge of grappling with the actual world and turning it into a story. There are others amongst us who don't quite get it and, yes, you need to show them something else. Like, "I go to the field, and then I—"; "I go to the field and I—"; "I go to the field or I"—do these other things.

ZIERLER: I wonder to what extent that's a very Caltech-centric perspective within geology. As you were saying before, you build your reputation—great science is building tools and enabling others. You analogized to the Human Genome Project, and I'm thinking of Lee Hood and gene sequencing and things like that. Would that not be the case at a state school where the expectation of faculty is they're not necessarily leading the field, they're not redefining the field, and that's a place where they might be relying on the tools that are created at a place like Caltech, and it's perfectly fine to go out and now do the yeoman's work, if you will, of collecting?

ASIMOW: I'm not sure the state schools would agree to that, and there's a lot of fantastic work that goes on at a lot of really good state schools, to be fair. [laughs] But, yes, I think there is some truth to that. And, yeah, it has been the history of this Division since the 1950s that we have geologists but we invested heavily in the discipline of geochemistry, some of which was cosmochemistry—analysis of meteorites and lunar rocks—but some of it was coupled to the field geology—go out and get rocks, understand the context, what they mean on the ground, but then find new ways to interrogate them in the laboratory with greater and greater sensitivity and precision to tease out what they might mean in ways that are just not obvious to someone whose tools are just their eyes and a rock hammer. Then we moved into planetary geology and planetary science more broadly, once it became clear that we were going to be able to either bring back samples from other planets, or get eyes, robotic eyes, on other planets, and somebody who knows what you do when you're walking around on the surface of a planet needs to be involved. That led to planetary science at Caltech as a major endeavor.

Likewise, our geobiology program is very much about bringing the tools of biology, especially microbiology, to interpreting the rock record and the deep time evolution of life. We have pioneered, or we've been involved in the pioneering, of a lot of ways to bring the rigor of affiliated sciences, be they chemistry or physics or biology or astronomy or mathematics, to deepening our understanding of the Earth. It is very easy, when you go too far down that road, to let the field geology wither, let other people do it. The Geology faculty within the Geological and Planetary Sciences Division try to hold the line against that and say, "No, we need to keep going out ourselves, getting our boots dirty, and feeding information and problems and challenges into all these other disciplines that are around us."

ZIERLER: Because ultimately for the next generation of tool-building, the next generation of discovery, you need that connection—to the Earth, literally.

ASIMOW: Right. There is sloppy work that can be done, say, in geochemistry, on samples divorced from their context. You can make very, very precise analyses of rocks, but if you don't actually know what the rocks were doing before you brought them back to the lab, you may well be missing something. Also, this relates to a principle that I have been observing of late. The Earth sciences have been moving recently into the era of Big Data. There are databases, readily available, with tens of thousands or hundreds of thousands of rock analyses in them that you can just download and then process. In our petrology reading group which meets every week, I have with tongue in cheek stated Asimow's Second Law, which is that "the amount of thought per sample that goes into a paper is inversely proportional to the number of samples considered." Or another way to think of that is that the good papers get above that curve [laughs], that hyperbolic curve of more thought per sample than average. But a paper really should be evaluated by how much thought went into it, and not how many samples it's based on.

ZIERLER: Deep thoughts about a few samples is always better than shallow thoughts about a lot of samples, is the idea.

ASIMOW: Yes. And you can't personally in a research career necessarily study 100,000 rocks. You can download 100,000 rocks from the database, but you're not going to understand any of them as well as the ones that you actually sampled.

ZIERLER: I want to pause on the field geology thread, because there is a gap in the chronology between when you get tenure and when you really start to embrace field geology. We ended last time, you were reflecting on the legacy of Tom Ahrens. When did you feel like the lab because fully yours, when you weren't simply continuing the work that he might have done had he stayed or been able to stay longer? Was it that 2010 paper? Was that sort of a marker for you?

ASIMOW: Yeah. Certainly that was the culmination of six or seven years of experimental effort, things that I proposed to do in the first round of proposals where I was co-PI or PI. NSF was patient enough to give me a couple of three-year awards to eventually lead to that one big paper. There were other papers along the way, but that was really where it was going. That paper, the authorship is Asimow and Ahrens.

ZIERLER: But this is a paper that he likely would not have written on his own?

ASIMOW: Right. He finished with this line of inquiry in the early 1990s, with work with his students Sally Rigden, Greg Miller, and Linda Rowan, and then had moved on to other things. In the early 2000s, I picked it up with the idea of extending it to much higher pressure, which was a technical challenge but opened up new intellectual opportunities. It took us a little time to figure out how to do it, and then it took us some time to do it, and then it took us some time to write it down. Tom retired in 2006, and I was already pretty much fully directing the lab by that point. He died on Thanksgiving 2010. For those last four years, he was a valuable consultant, but certainly I was driving. No, he wouldn't have written that 2010 paper. We actually—while Tom was still alive, we hired a postdoc, a Russian scientist named Oleg Fat'yanov, who stayed too long to be a postdoc and so he became staff for many years.

ZIERLER: A recurring theme in your career.

ASIMOW: A recurring theme. He went back to Russia in maybe—it has been some years now; I don't know, 2016—with a couple of papers unfinished. We finished one of them. We are just about to finish the other one. This paper will probably come out in 2023, and it's debatable whether we should make Tom a coauthor. I think we will acknowledge his contributions, in this case. But when Oleg finally kind of put all the data together and felt like he was ready to write the paper, he said, "I really wish I could have shown this to Tom."

ZIERLER: In singling out the 2010 paper—you emphasized its significance—there's the duality of an inward-looking assessment and an outward-looking assessment. Even before you saw its impact—the citations, the way it changed the field—what did you see yourself before you released it out into the world that was so significant? What was the significance of the work?

ASIMOW: It was just—it was complete. [laughs] It was not complete in the sense that there was nothing more to do but it was definitely finishing a chapter, in that it dealt with three model compositions that Tom and Ed Stolper and Sally Rigden started working on in like 1984, and I managed to get enough data on all three of them to extend that work up to like five or six times higher pressure than they had been able to go to. Once you have three compositions that plot along a line in composition space, you can do a test of whether you can predict the properties of the intermediate composition by averaging the properties of the end members. It takes three compositions to do that. Those three do plot along the line, and so I was able to do that. If you can establish that that is true at least for that one case, then you have confidence that the problem of understanding all possible liquid compositions is tractable. If you don't have that linear mixing rule, then you'd kind of need to study every possible composition separately. If you can predict the properties of mixtures from the properties of end members, then you just have to study the end members. Plus a couple of mixtures to verify that the mixing theory works. So I really wanted to be able to apply that test to these data, so I had to finish complete, coherent data sets for three compositions.

The other part of the story is, at about the same time, in around, I don't know, 2006, 2007, 2008, somewhere in there, we noticed from our shock wave data on several compositions that there was a behavior in the thermodynamic properties of liquids that was entirely unexpected to us, and entirely opposite to the way solids behave. At the same time, a theory group that was doing ab initio molecular dynamics calculations made the same observation. The representation of that idea in the papers we wrote in 2008 and 2009 was pretty good, but that's also in the 2010 paper that I really, with one extra key experiment, was really able to nail that behavior very precisely and very specifically and very confidently. After I had that paper, it led to some further work where I really was able to claim that this behavior of liquids under compression is universal and that we see it in all the silicate liquids we had looked at. I wasn't confident saying that until I had seen it in all three of those compositions that went into that paper.

ZIERLER: All of this work—the tenure decision is obviously made based on what you've accomplished now, but there is some element to it about what's entrained and what your future prospects of impact were. Did you feel like all of this work sealed the deal in your own mind in terms of not just what you accomplished circa 2006 but the plan you had established to really finalize everything and to make the broader impact four years later?

ASIMOW: Right. At that point, I knew how to do those experiments, I knew they worked, I knew they were surprising compared to the previous results, and I knew that just turning the crank for a few more years it would be a substantial work. So, yeah, by 2005 or 2006, I knew that that was going to work. Just took a little while to finish it.

ZIERLER: The serendipity of the cold call from Egypt, had you sort of had an itch to get into field geology and that was the thing that pulled you in? Were you not thinking about it at that time?

ASIMOW: For the record, I still haven't actually gone to Egypt [laughs] and gotten my own boots dusty. I was going to go in 2020.

ZIERLER: COVID.

ASIMOW: Yeah.

ZIERLER: But this is what you cite generally as pulling you into the world of field research.

ASIMOW: Yeah. A couple things happened at that point. One is I started analyzing a lot more actual rocks instead of just experimental samples. Another thing is, a couple years later, Claire arrived and put this very nice laboratory right across the hall from my office that gives us the capability to make ourselves measurements that we used to have to send out to a commercial lab, and she doesn't charge me nearly as much as the commercial labs do. Without having to write a proposal to raise money, I can process significant numbers of rocks that would have been difficult without access to Claire's lab. So, there's that.

ZIERLER: What are her capabilities? What does that lab do for you?

ASIMOW: She has an x-ray fluorescence spectrometer that allows us to measure the chemical composition of whole rocks. What we previously had was just microanalytical capability, where you take a rock, you make a polished section of it, and you study it at the level of the individual minerals that make it up. But you want to be able to both see what minerals are there, what compositions and textures the minerals have, but also, what's the total inventory of available elements in the rock to go into those minerals. It's two complementary ways to consider the chemistry of a rock. At some level—and critics said this when Claire said that's what she wanted to put in her lab—"That's such routine measurements. Why go to the trouble of building your own lab and calibrating your own lab and keeping it running? Why not just send this stuff out?" Two reasons: one, it's cheaper. Two, you get to train students to actually generate the data and know what goes into it, which people who send their rocks off to some commercial lab never see, and think they never need to know. And I think that's dangerous. This has been interesting—over the years since that lab got installed, and since I've had my own students and various visiting students, I've had several visiting students from China, and for them, the idea of actually processing their own rocks and generating their own data and not sending it off to some commercial lab is very foreign, and I think very educational for them. Claire's machine can measure all the major elements, the elements that are present at kind of half a weight percent and higher concentrations.

We also have, thanks to what is now called the Resnick Water and Environment Lab, an instrument that can measure the trace elements, if you can get them into the machine. There's two ways to do that. One is by laser ablation. You zap your rock with a laser, and you take the debris that comes off and accelerate it into the mass spectrometer. The other is by solution. You get your rock dissolved in a liquid solution and then the machine can aspirate the liquid through a straw and spray it into the mass spectrometer. My student, Maddie Lewis, was the first to really complete the pipeline of taking a sample, running it through Claire's x-ray fluorescence spectrometer, and then taking a small piece of the fused bead on which we do the XRF measurement, dissolving that in relatively weak acid, and getting it into the ICP-MS so we can measure major and trace elements all in the same sample. Again, I could send it out to a commercial lab to do that for, I don't know, 150 bucks a sample. But now we can do it here, mass production, lots of samples, for $25, and my students learn to actually do it, and see what's involved. How do you run blanks to keep track of contamination? How do you run standards to calibrate the machine? What do you do about drift? Do you understand the difference between detection limits and precision and sensitivity and all the ways that one would like to characterize data? Which kind of underlies one of the things that I like to say to students, which is that the most important and neglected thing in science is understanding uncertainty. If you actually know what your errors are, you'll never be wrong. You might be trivial if your errors are too big to actually address the question, but you won't be wrong. [laughs] And so, I think it's very good training for students to actually make these measurements themselves.

ZIERLER: It sounds like vertical integration is really an ideal here.

ASIMOW: Yeah. And maybe what that means is, we're always going to be kind of slow and inefficient, not accepting division of labor as a principle.

ZIERLER: But skill building is really the ideal here, that they're involved at each step of the process. There's not something to outsource.

ASIMOW: Yeah. Unless it's just so massively more efficient to outsource it that you have to, but it hasn't been. So, we had the confluence of people come to me with interesting field-based problems, I have access to analytical resources at low cost to process their rocks, I have modeling tools to think about how do you interpret the data that come out the other end of that process, and yes, where possible and when possible, I do have this desire to actually get out and see these field areas and participate in the geology part and not just the geochemistry part.

Maintaining Sample Integrity

ZIERLER: Some nuts-and-bolts questions before we return to when you actually do get your boots dusty—samples either you get them or they come to you, are there any sort of contamination considerations? Are you in the field, you throw it in a box, and you mail it to Professor Asimow, and that's all there is? Or, are there separate steps along the way to make sure that you have clean samples, whatever that means?

ASIMOW: Generally speaking, a rock that you pick up in the field while it's still a rock is fairly hard to contaminate, but once you start processing it, especially if you are selectively enriching some element, it becomes very easy to selectively enrich contamination as well as sample. There are clean labs and there are dirty labs. Mostly, I work in dirty labs because I'm not doing those kind of selective enrichments to try to isolate some relatively rare element and make sure that all of the atoms of that element that I'm processing came from the sample. My colleagues over the years—Clair Patterson, Gerry Wasserburg, François Tissot—who are working on trace elements and the isotopes of those elements, and they really need to control for contamination, that's a whole different enterprise. For the most part, usually, I'm not that worried about contamination, because I'm not working on really low-concentration elements and I'm not enriching them. If you have a sample of DNA and you're going to do PCR on it, to massively enrich the amount of DNA so that you can make bulk measurements on it, it's very easy to selectively enrich somebody else's DNA instead of the specimen you're trying to process. Similar problem.

At the same time, there are definitely ways to contaminate samples. Right now, I have a set of rocks, set of powders that were sent to me by a collaborator in Egypt, a different one than the one I've mostly worked with. We analyzed them, and we had analyzed other rocks right before, and we had analyzed other rocks right after, and only these rocks have freakishly elevated tungsten and niobium and titanium concentrations. The collaborator from Egypt wrote back and said, "They are obviously bad." I said, "Yes, they are. But we ran other samples right before them, and we ran other samples right after them with exactly the same procedure, and they're not anomalously enriched in tungsten or niobium or titanium. Did you perchance grind these rocks in a tungsten carbide shatterbox to make the powders? He said, "No, I ground them in silica." So, we haven't figured out actually what's wrong with those samples. They're clearly contaminated [laughs] but we don't know if it happened there or here.

ZIERLER: Is there also with contamination a distinction between the surface of a rock and its interior? Is there a prophylactic—

ASIMOW: Absolutely. It's standard practice, when you get a rock, to cut off the weathered surfaces that have seen the air, with a rock saw, and then polish off the saw cuts so that you don't end up analyzing stuff that gets just scraped off the saw blade, to get an interior sample, and then that should be what you grind to a powder for whole rock analysis.

ZIERLER: It's understood that that interior is generally impervious to the elements and saws and things like that?

ASIMOW: Less pervious.

ZIERLER: Less pervious.

ASIMOW: There are tests that you apply to decide whether a sample is actually fresh and the extent to which it has been affected by recent weathering or alteration or metamorphism. Sometimes it's the alteration and metamorphism and even the weathering you might want to study. But if that's not what you want to study, then you need to filter for samples that have been affected.

ZIERLER: This is related to contamination, but a way-off tangent. The debate about Mars sample return and concerns about the Pandora's box of what might be released when we start to analyze these samples, do you have an opinion? Do you have a concern in this regard?

ASIMOW: I am much more concerned about us contaminating those samples with terrestrial material than those samples having any effect on the Earth. Planetary Protection is what NASA calls this. If you're going to another planet, you don't want to spoil it. That's important. And if you're bringing samples back you want to make sure that what you measure in the samples is intrinsic to the samples. I think those are real risks. I think personally danger to the Earth from things that we are bringing back from other planets is not a real threat. That's my opinion. I don't think there's any viable organisms in Martian rocks that could get out and cause a disease.

ZIERLER: Mars sample return is drilling, what, six, eight inches into the surface of Mars?

ASIMOW: More like three, I think.

ZIERLER: Three inches, okay. So your lack of concern is not—we're not extrapolating that to there's no life on Mars; it's just that at that—?

ASIMOW: Oh, I'm willing to go there.

ZIERLER: You're willing to go there, also?

ASIMOW: Yeah. There may have been life on Mars, maybe. I'm willing to conclude that there isn't life on Mars [laughs] based on all the evidence that is available to me and what I know about the environment.

ZIERLER: Even the subsurface, even the possibility of water and caves and caverns and all that?

ASIMOW: I would be shocked. [laughs] In fact, personally, I wish that NASA would be willing to play up and advertise and motivate missions to Mars on the basis of something other than the search for life. Or even the search for past life. I think there's lots of reasons to study Mars, and that's not the best one, because if we never actually find life, then you could say, "Well, what was all that money for?" So, no, I don't believe there is life on Mars. But, okay, at the same time, I don't know. [laughs] I am a scientist. I accept that we work by disproving things and you have to consider things until they have been disproven. You can never positively disprove the existence of life on Mars because you're never going to sample the entire planet. I don't know. To me it just doesn't seem like a credible threat.

ZIERLER: On the basis of those three inches and the inhabitability of the surface of Mars, that's where you're coming from? That's why there's a lack of concern?

ASIMOW: Yeah.

ZIERLER: And is it only biological? What about radiological? Are there radioactive concerns about Mars? Nothing like that?

ASIMOW: Radioactive elements are the same [laughs] here, or there. That's funny.

ZIERLER: There isn't like super Martian plutonium that we might not know about that could cause a real problem?

ASIMOW: No.

ZIERLER: That's science fiction?

ASIMOW: Yes. Speaking of which, I just re-read the Foundation books, by Asimov, and towards the end of the later books, they get into the search for the original Earth. At that point in that imagined universe, humanity has been dispersed through the galaxy for so long that nobody even necessarily accepts that there was a home planet, except a few people. But it builds on the theme that was in the Robots novels that the Earth became radioactive, and became uninhabitable, and humanity had to leave. Some of the characters in Foundation say, "That's not how radioactivity works!" [laughs] But, no, there's no weird [laughs] contaminants from Mars that could irradiate the Earth. Just—no. [laughs]

ZIERLER: I asked a Mars-specific question; now we can think way afield, beyond 2028—sample return for icy worlds. There is a lot of excitement, possibly, that there's life under the ice there. Would you take a different tack in terms of security concerns bringing samples back from icy worlds here, because there might well be life in them?

ASIMOW: Again, I would be much more worried about us contaminating that world and coming back a few years later and finding that it's full of terrestrial life, than the opposite. But, yeah, to me, that feels actually more plausible—that we could bring back something viable. On the other hand, the probability that anything alive that we brought back would be able to harm terrestrial life, interact with terrestrial life, infect terrestrial life, that seems really far-fetched. All terrestrial life is descended from the last universal common ancestor, and we all share a bunch of really deeply rooted fundamental chemical and biochemical processes. Viruses have had some billions of years to work out what those processes are and how to take advantage of them, so when you bring an unfamiliar virus, when you bring smallpox to the new world, it's still terrestrial life, and it's able to infect what it finds when it gets there. Extraterrestrial life being able to do anything to us, other than shoot us with ray guns, I don't think that's plausible. Even if the Earth is habitable for organisms that evolved on another world, it seems like they could only do harm by propagating to the point where they just take up all the space and push the terrestrial life out of the way, compete for resources; not cause disease. Now that all that is on the record officially, let me say I am neither a biologist nor an astrobiologist, and these are my uninformed opinions [laughs] from what I know from listening to biologists and geobiologists and astrobiologists and forming my own opinion.

ZIERLER: Okay! [laughs] Glad I got you on the record. I want to return to the 2013-2014 timeframe. The randomness of the cold call, had you received similar calls in earlier years and they did not seem interesting to you, or were you kind of just waiting for something to happen and then you would jump in? How did that work?

ASIMOW: I guess I'm always open to offers of collaboration and people that are interested in visiting.

ZIERLER: Had you received earlier calls, similar?

ASIMOW: Yes, and I had hosted other visitors; this particular one just turned out to be the most productive, over the long term. It used to be easier for Chinese scientists to come and visit. Very difficult now, but I've had both visiting students and visiting faculty from China that have come and we've had some productive collaborations, led to a few papers, but didn't generate as much continuing energy. It was more short-term.

ZIERLER: What was it about the Egyptian research that necessitated 30 papers? That's a lot!

ASIMOW: [laughs] Yeah. Partly that Mokhles feels pressure to publish a lot. Partly that the exposure is really good. It's the desert, and so you can get fresh rocks everywhere you go. They aren't all covered with mud and vegetation. Partly that the kinds of problems, the kinds of rocks that are exposed there, are the kind that I actually have things to say about. Somebody might have some field area where they've got lots of interesting rocks, but they aren't interesting to me, necessarily.

ZIERLER: These 30 papers are all from the same sample, or this is a variety of samples?

ASIMOW: A variety of samples, the whole essentially range of igneous petrology from mantle-related rocks, which are very low in silica, to extremely silica-rich granites and everything in between. Many of them are interesting because they concentrate potentially valuable metals. This is really the justification for the work as a whole, is that I believe—we believe—that the 21st century is going to be very much the century of metals in the way that the 20th century was the century of petroleum. That if we are going to decarbonize the economy and stop burning fossil fuel, we are going to rely on a bunch of other technologies, many of which rely on a reliable supply of particular, and in some cases rare and expensive, metals. The most obvious example perhaps is that you need cobalt to make lithium ion batteries work, with current technology, and that has its whole associated set of social and cultural problems in the places where cobalt is to be found. There is also the whole rare Earth element thing. Most rare Earth elements used to come from the Mountain Pass Mine along I-15 on the way to Las Vegas. Mountain Pass shut down because it became subeconomic because other sources of rare Earth elements in China became much cheaper. Then sort of nobody noticed that basically China managed to accumulate a monopoly on rare Earth element production until they started rattling their saber and threatening to deny rare Earth elements to Japan a few years ago. Then somebody noticed that a Chinese company was trying to buy Mountain Pass. Now, everybody's like, "Oh my god, rare Earth elements, we need to replace all of the expertise that retired, in where you find rare Earth elements and how you produce them." You need neodymium for magnets, and you need erbium for optical fibers, and each of them has its own special properties for various things ranging from solar panels to batteries to optical fiber to magnets to superconductors to you name it.

Each element in the periodic table potentially has some killer app where it's going to be a key technology that will allow us to efficiently build electric cars and electric airplanes and storage for power and solar panels and all these things that we need to build in large amounts to replace petroleum. I'm not really an economic geologist. It's not my training; I'm more of an igneous petrologist. But a lot of these metals are found in igneous rocks so they are related fields. I accept the argument that the more countries get production going, get sources of these metals, the more stable the overall world economy is going to be, the less geostrategic risk of things like China developing a monopoly of rare Earth elements, or Congo developing this ridiculous child labor market because of artisanal mining of cobalt. It's better to have broadly distributed sources of all of these metals.

That's mostly what I'm after in West Africa, is finding sources of metals, and finding them in a way that avoids the resource trap, classic underdeveloped country that has valuable resources but they get captured by the elite and they just get used to prop up a corrupt government. My approach to that is find these and publish them in the open literature, so everybody knows where they are, and maybe, optimistically, that mitigates against the exploration being done by corporate interests, which can capture the government, which can propagate endemic corruption. Ideally, as a scientist, I can make a difference by, even if I am not going to go and develop these mineral resources myself, developing tools for finding them, finding resources, and saying out loud where I found them.

ZIERLER: Now, these samples that, as you've said, were of interest to you, was it specifically the metals and the translational possibility, or that was a realization that developed over time?

ASIMOW: The latter.

ZIERLER: What was initially interesting about these samples from Egypt?

ASIMOW: A lot of things, because they are quite a diversity of rocks. One example is that there's a suite of rocks that geologists call an ophiolite complex, which are fossil pieces of ocean crust that have found their way up onto land through various accidents of tectonics. Ophiolites have been known for some time and studied in some detail, and they were understood well enough that when marine research and ocean drilling got to the point where it could sample enough of the ocean crust to see what's out there, people immediately recognized, "Oh, this is an ophiolite sequence in place. We know this sequence of rocks. We recognize it." There are a few very well preserved ophiolites that have been very intensively studied that are of particular ages. The best is probably, arguably, in the Sultanate of Oman, on the west side of the Persian Gulf. That one is roundabout 100 million years old. There's another one in Cyprus. There's another one in Newfoundland. There's a bunch of them in Egypt that are 700, 800 million years old. They're not nearly as well preserved; they're pretty complicated. But it gives us an opportunity to address what ocean crust looked like a long time ago and try to decide whether it's similar to the way it looks now, or not.

Also, there are different varieties of ocean crust. There's the variety that forms out in the middle of the ocean at a regular mid-ocean ridge. There's the variety that forms at a convergent plate boundary, either in the back-arc, like behind the Mariana chain, or the fore-arc, in front of the volcano chain about a subduction zone. There aren't that many examples of modern fore-arcs that you can study, because they're underwater. There has been some drilling in the Mariana fore-arc, in the Izu-Bonin fore-arc. But most of these Egyptian rocks seem to be very similar to modern fore-arc basalts, and so it's actually an interesting puzzle to understand why there's so much of that, because it's kind of a rare process, today. So there's themes of uniformitarianism: Can we use observations we make on the Earth today to understand the past? There's also secular change: how is the past actually different, and when does that uniformitarian analogy start to fail? Those are good questions, fun to work on.

ZIERLER: Here's where you can square the circle. Your whole career up until the Egypt project, you were getting samples from colleagues, you were analyzing them, you were doing your laboratory work, your computational work. But you emphasized that the Egypt work sort of compelled you to think about becoming a field geologist, or at least doing more field geology yourself. What's different? What's different about this particular thread for you?

ASIMOW: I don't know. It's just time. It's just—

ZIERLER: The parallel universe question—if he had called five years earlier, would this not have been the thing to get you out into the field, because that's not where you were in your career?

ASIMOW: [pause] I can't say. There is an argument for that—that the shock wave work was not mature enough yet for me to take my eyes off it.

ZIERLER: It demanded all of your attention, essentially.

ASIMOW: Yeah. Also, my children were younger, and that makes it more difficult to get out and travel for long periods. I had my first child when I was in graduate school, 1996, and my third a couple years after I got tenure, in 2007. Most of my field training was in my first years of graduate school when I was not yet a father. The seagoing expedition that I went on was in the fall of 2004, before my middle son was born. Then, yeah, it wasn't a good time for a number of years, to really get away. Obviously some people manage to run field-going campaigns or do a lot of business travel when they have small kids. It wasn't my choice, to do that. The last few years that I have started going out and doing longer trips, my kids are older and easier to leave for longer periods of time.

ZIERLER: So, 2014, it's really a combination. There's the personal. It's that your lab is at a place where you can afford to be gone for long stretches of time. And you just—felt the need. It was time.

ASIMOW: Yeah.

Making Choices on a Big Planet

ZIERLER: For the remainder of our talk today, last few minutes, it's a big planet, lots of places to go. You've already told me you don't have the nose to really lead you to the winning spot. Once you're ready to hit go, how do you choose? Where do you go first? What's most important?

ASIMOW: There's a few answers to that question. One is, where can you get to? And, who has already been there? And, what are the environmental and cultural consequences of going there? Field geology is experiencing something of a crisis of conscience, with indigenous land rights and the environmental consequences of fieldwork and sampling, and so I want to make sure that I'm going to places where everybody agrees that it's okay for me to be there, and for me to pick up rocks there.

ZIERLER: The timing, 2014, this is really when the problem with the TMT in Mauna Kea starts to become apparent. Did that register with you at all? It's astronomy, it's a different field, but the larger considerations of neocolonialism, science from the Western world, was that sort of in the milieu at that point?

ASIMOW: Well, it is now, in that on the one hand I'm the chair of the GPS Diversity, Equity, and Inclusion Committee. On the other hand, I run an annual trip for our graduating seniors to the big island of Hawaii. And, it is part of the conversation now that we don't just go to the top of Mauna Kea and visit the Keck Observatory and say, "This is awesome. This is really cool." We stop and we think about the other side, the other point of view, and whose island it is. When Bob Sharp was running that trip, we always—acknowledged—indigenous traditions and mythology. We made a sacrifice to Pele before tromping all over her volcano. But there's a real hunger amongst the students now to put some more energy and thought and attention into questions of whose land is it and what are we doing here and are we minimizing our impact and are we working cooperatively with all the stakeholders. It is important. Some of that pressure is coming from the students, from the young generation. But they also ought to be taught about these questions and not just kind of left to figure them out for themselves. So, yes. I don't know that I can put a particular date on it, but certainly coming back to go to Hawaii again after the pandemic, the conversation has changed. I'm going to be running an expedition, an enrichment trip as we call it, to Iceland this August. Iceland is different from Hawaii or the United States or Africa in that it has never been colonized. The people that live in Iceland are the Icelandic people, and any conquering that went on was a very long time ago. [laughs] So, I feel like that's going to feel a little bit different than a number of places that I have been where you always have in the back of my mind the question of ownership and land rights and cultural sensitivity.

You were asking, where would I go? Maybe I would go to Europe [laughs], because of that. But also, my recent student Joe Biasi, who is going to be a professor at the University of Wyoming come next year, he has this love for the Arctic and the Antarctic, for the polar regions, and I kind of inherited that from him. He came along to Baffin Island. He organized this trip we did to the Yukon and Alaska in 2019. I've not yet been to Antarctica. I would like to go to Antarctica. Seems like a funny place to go to study rocks because so much of it is covered by ice, but where the rocks are showing they're very interesting, and not very well studied.

ZIERLER: I imagine the rocks in Europe are very well studied.

ASIMOW: Right. But—there's always another way to look at it.

ZIERLER: Have you found that holy grail yet yourself, in your fieldwork? That perfect mix of it's not typical, but it's also more important than where you're currently looking?

ASIMOW: Of the field-based papers that I have been involved with, I think the one that is most highly cited and most influential is one that was done here in the Southern Sierras, mostly by Jason Saleeby and his student, Lingsen Zeng, that I was invited to participate in, that really set out in my view a new paradigm for understanding the way you interpret the isotopic composition of igneous rocks. There's a place called the Goat Ranch pluton, just south of Lake Isabella. It's not obviously different from any other such subduction related pluton, but it was a well-executed study with some very original thinking that went into it, and it changed the way people think about the problem. So—yes! It has happened.

ZIERLER: Last question for today. I'll invert how we began the conversation, about how you might have seen fieldwork as a completion to your laboratory and computational work. All the fieldwork that you have done, has it enriched the computational and experimental work? Has it gone the other way, where it has changed the way you're running the lab, the way you're building your tools?

ASIMOW: It hasn't significantly affected what I'm doing with shock waves because that's mostly either about meteorites or about the deep Earth. It's not closely associated with terrestrial impact craters or much less any other phenomenon we can study in the field at the surface of the Earth. On the experimental side, there's certainly more potential for feedback of identifying questions that arise when we try to understand a field area where we just don't have the basic process information, and we need to do experiments to interpret that. What it has mostly fed back into is the computational work and the realization that a really good thermodynamic model that accurately predicts mineral melt equilibria, which we think we have, is only as good as the paradigm in which you use and apply and interpret it. Getting out in the field and collecting the real rocks and seeing the level of complexity in them is making me understand that some of the paradigms that we use are just not adequate to the problem. The simple version of that is, a lot of my early work in igneous petrology focused on basaltic rocks, and basaltic volcanic rocks, which erupt as liquids. Maybe they're carrying a few crystals, but they're mostly liquids.

The way that we think about the evolution of igneous rocks, influenced by an important book known as The Evolution of Igneous Rocks by Norman Bowen, is that they evolved by fractional crystallization along what we call a liquid line of descent. You start with a liquid at high temperature. As you cool it, it partly crystallizes. You take the solids out, throw them away, and you follow the liquid as it changes. Maybe that liquid erupts and becomes a volcanic rock. But most of the time when you pick up a rock, it's not a liquid; it's a pile of crystals. At some level, we all imagine that it's a pile of crystals now, but it represents the composition of a liquid. But that's not necessarily true. The more you get towards granites and plutonic felsic rocks, I think the less and less true it is that your bulk composition of your rock can be thought of as a liquid composition. My model is really good for following liquid compositions. It also tells me the solid compositions along the way. But I haven't quite wrapped my head around when I pick up a rock, and it's neither a liquid composition nor purely a pile of solids but something in between, how do I deal with that? How do I think about it? How do I systematically generate understanding of an assemblage of rocks when I can't make either the simplifying assumption that they're purely a pile of solids, or purely a quenched liquid composition? I don't think anybody has a good answer to that. That's the hard problem that my studies of granites in the field and my ability to model some aspects of them but not yet all of them—that's where my thinking is right now.

ZIERLER: Okay! Next time, I think we'll be able to pick up and go right to the present.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Tuesday, June 6th, 2023. It is great to be back once again with Professor Paul Asimow. Paul, thank you again for having me.

ASIMOW: You're welcome. Good morning.

The Multidimensional Value of Faculty Service Work

ZIERLER: Today, we're going to cover two major topics to wrap up our excellent series of discussions. I want to cover the importance of departmental and institutional service for you, and generally what that means for professors at Caltech, and then also to circle back to your earlier interests in non-terrestrial science, and where JPL might have started to play a more recent factor into your research. Then we'll end with some retrospective questions to bring it all together. Maybe we could start first with an administrative-philosophical question for professors. What do you think should be the expectations of junior faculty in terms of service? Should they be exclusively focused on the scholarship, on the science, or is there room and a need for them to be involved in divisional or Institute matters?

ASIMOW: Absolutely the latter. You can't overwhelm them with labor-intensive service projects but they need to be involved. You can't just have the old folks running things, and you need to start building the culture, the idea of faculty governance and of shared responsibility for the welfare of students and the welfare of the Institute from the beginning of somebody's faculty career. I think if you keep that away from them for their first six years, it's too late, by the time you say, "Okay, now you have tenure, we're going to dump all these burdensome jobs on you." If they've already gotten into the habit of assuming that everybody else is running things, it's not the same.

ZIERLER: What kinds of service did you do as a junior faculty member? What was important for you to get involved in, and what were you asked to do?

ASIMOW: By tradition in the GPS Division, the newest faculty members organize the division seminar series—find the speakers, make sure somebody is available each week to host them. I did that for a year. In my case, because of the work that I was doing, it made sense for me to right away get involved in managing the analytical facility. We have a committee that oversees the operation of the electron probe and the scanning electron microscope and instruments like that, which I'm a user of, so it made sense to involve me in the management of those. Also because I run large and potentially dangerous lab operations, I have been involved with the safety committee that works with Environmental Health and Safety to make sure that each lab has a safety manager and those safety managers are trained and that new people coming in are trained, and that when there are questions of policy, somebody is looking over them. I have been on several search committees. While you want a senior faculty member probably chairing a search committee, it's appropriate to have junior faculty members involved in doing the search. That is another area that I have been active in, within the Division. Also, it's appropriate for junior faculty members to get involved in Institute governance, because Caltech has a really unusually strong tradition—it's partly a function of history and partly a function of size—that almost everybody working in administration is a researcher. They have active research programs. They are not full-time career administrators. Caltech is not very good at cultivating career administrators and we don't really respect it as a career path. Part of working towards that goal is having junior faculty members involved in the faculty committees, potentially on the faculty board, just paying attention to what is going on around the Institute, as much as possible.

The faculty board has a whole bunch of standing committees. Some of them have real purposes and they need to exist because they have a definite function. Some of them are kind of zombies and are just there because the bylaws say they should be there, and they don't necessarily [laughs] have that much function. More or less at random, not for any preordained reason, I was asked to serve on the student housing committee when I was really very new, maybe my second year or something like that. I was on that committee for nine years, and I chaired it for three years. No, I think I chaired it for six years. You're only supposed to chair a committee for three years, but it was not a difficult committee, and nobody else on the committee wanted to do it, so I think I did it for two terms.

In that role, I found that I could be effective if the vice president for Student Affairs viewed me as a trusted partner, and when issues came up with housing was willing to hand them to me and my committee for deliberation instead of just deciding something. That sort of partnership model worked well, and I kind of saw it as my role to defend the house system [laughs] against critics. Not that it can't be reformed, but there's always a movement to just get rid of it and replace the—keep the physical infrastructure and replace it with basically a zero-culture dorm [laughs] world, which I think would be a great disservice to the students. The house system is not perfect, but it is the students' most important support system and most important culture and most important source of loyalty. Plenty of Caltech students will tell you that they are more loyal to their house than to the Institute. So, I spent some years working with the student leadership and other faculty members and the vice president for Student Affairs to keep the house system rolling and stable and updated for the needs of a more diverse student body moving into the 21st century, which is when I was doing it. At the same time, the student housing committee is not that important a committee. Housing can run itself. Dining can run itself. The faculty committee used to see the housing contract and the housing rates before they were sent out, and then the more sort of professional housing managers decided they didn't really need faculty input on that and stopped asking.

But apart from defending the house system, the other way I describe the role of a faculty-led student housing committee is to stop housing from being run too professionally. [laughs] It's not just a landlord, right? It's an organization trying to facilitate student life and keep some academic character and some flexibility in the rules and meet students where they are, instead of necessarily expecting them to behave like fully grown up tenants living in private apartments. So, I enjoyed doing that work for a number of years. I pride myself on being one of the faculty members that actually knows something about student life and about the house system and about the difference between the houses and how the students view their residential system. I think that Anneila Sargent, who was vice president for Student Affairs in those days, appreciated having me in that role, and I appreciated doing that work for a while. After I got tenure, so I was more senior at this point, I was asked to serve on the freshman admissions committee. That is a committee that definitely does have a job and really needs to exist, in my opinion. Although, again, Caltech is a total outlier in this regard of having faculty at large closely involved in freshman admissions.

ZIERLER: Is this the kind of service that would only be asked of somebody who has tenure, because of the commitment?

ASIMOW: It is viewed as one of the more labor-intensive committee assignments. I don't know that a junior faculty wouldn't be asked, but generally speaking, it tends to be senior faculty members. I stepped in, in the middle of a term, when some other member of the committee rotated off or had to go on sabbatical or go out in the field or something like that. Caltech has a professional admissions staff, but they also have faculty members, and they used to have students, reading admission files and giving their input, and shaping the process both directly through the particular student files that they endorsed, but also through what they wrote about why they were endorsing student files, which would go back to the professional admissions staff and help to shape their sense of what the Institute wants, rather than that just coming from the director of Admissions or from the provost or wherever. However that kind of culture of what a university is looking for propagates through admissions staff at most schools, here there's constant input and steering by the faculty chair of the freshman admissions committee and by the faculty members that are reading files and commenting on them. Students no longer read files. That was a very strange governance event. Somebody noticed that the freshman admissions committee was in violation of the bylaws because it's a faculty committee that was more than one third student reps, and the rules require that all faculty committees be at least two thirds faculty. As part of reconstituting the committee to be consistent with the bylaws, somebody realized that it maybe wasn't that appropriate to have students reading admission files of students who would then come in future years and be their—not classmates, but be here at the same time.

ZIERLER: There's privacy issues, that kind of thing.

ASIMOW: Privacy issues, and there wasn't any good way to redact in a way that made sense. So, student reps on the admission committee now do not read files. They advise on things that they know better than the faculty or the admissions counselors, things like what robotics contests are real and which ones are fake. Also, they're very involved in recruiting and yield activities. So, they're in an advisory role. But the faculty are still actively reading files. There's a constant struggle to get enough faculty on the committee to be able to read a significant fraction of the files and preserve that role. Because it's very easy to have, especially as the number of applications keeps going up and up and up—it was 7,000 when I started on the admissions committee; it's 15,000 now—the faculty can only read about 1,000 or 1,500 files, maybe, and so there's a very aggressive filtering before the files get to the faculty. But if only the obvious admits are getting to the faculty, then there's no point in having the faculty read the files. So, there's a balance that has to take place. The admissions staff has to let through to the faculty enough files that there are still some questions about and some discussion that can take place, and there have to be enough faculty reading enough files to make a dent in the pile of applications that come in.

ZIERLER: A variety of questions on admissions, because Caltech has a unique approach to that. But just before we get there, to stay on the junior faculty side of things, just one question there. Is divisional or Institute service a factor in tenure decisions? Should it be?

ASIMOW: Yes, and nominally it is, but it doesn't carry very much weight.

ZIERLER: It will never be a make-or-break decision.

ASIMOW: Right. And [pause] I don't think it really should. Teaching, yes. Mentorship, yes. Research, obviously. But service to the Institute, while important, and it is great if we have a cadre of faculty that are dedicated to it, I don't see it as being likely ever to be a deciding factor in a tenure decision. Which may be part of why it's a struggle to find faculty members to fill committee chairs and leadership roles and to get involved in student life. But I think there's other reasons for that.

ZIERLER: Service is a sign of who will be a good colleague in the long term, though. It does help make those kinds of decisions.

ASIMOW: Agreed. I think at a larger scale, I have a theory [laughs] about the change in people's perception over time, over decades, of what it means to be a university professor. It used to really be a lifestyle choice and not a nine-to-five job. To a significant extent, that was—in the sort of English system of like Oxford dons, it more or less amounts to university professors choosing to be bachelors for life. In the American system, it was more supported by having stay-at-home spouses who didn't mind or didn't object to people staying at work after hours. But the more faculty have working spouses and two-career families and the further they live from campus, and in general the more insular American culture becomes about kind of protecting hours at home, the more difficult it is to have faculty involved with students outside of class and lab and to do anything that involves staying after-hours. I think it's related to the phenomenon that was captured by a social scientist in the book Bowling Alone that basically said people used to belong to bowling leagues, and go out and socialize in groups after hours, and nobody does anymore. Maybe they still bowl, but they just go and bowl and come home.

So, American culture at large has become less social, and in my opinion one side effect of that is that university professors are much less accessible to socialize with students and to lead by example outside of the classroom and outside of the lab. There's just only a few faculty that will be faculty in residence and live on campus, or will go out of their way to go to house dinners, or lead clubs, or all these sorts of things that I think it's pretty important for the student experience that faculty members be willing to do that. When I do things involving student life, I typically see the same handful of professors everywhere I go. Could you change that by changing the tenure standards? I suppose. But so far, I've not seen a movement to do that. I think hiring and looking for people who are interested in teaching and mentorship and student life at the assistant professor level and who have already demonstrated that through mentorship when they were grad students or postdocs is a reasonably effective way to do it.

Making Geology More Inclusive

ZIERLER: I want to return to—I think it was in our first conversation—your realization that when your father took you out and you appreciated nature, at a certain point you recognized what a privilege this was that many don't have, and that has since translated to your commitment to make the Division, science in general, Caltech, more diverse, more inclusive. That's where the question is headed. The origins of it are, as you probably know, Caltech has had a spotty record in its deep history of its admission standards—very few African American students, still; restrictions, quotas against Jewish students in the 1940s and 1950s; no admission of women undergraduates until 1970. Where are things today, and how can the admissions committee work at the best possible level to make Caltech the kind of institute you want it to be?

ASIMOW: In my time involved with freshman admissions and all the time that I've been involved with graduate admissions, which is all the time that I've been here—because the faculty as a whole in GPS do graduate admissions; there's no admissions committee, we all do it—I have seen no discrimination of any kind. I have seen a commitment to inclusion, or at worst a commitment to neutrality, amongst all of my colleagues and everyone involved. And so, the problem, or the source of lack of diversity, is not anymore overt discrimination. It's not even implicit bias. It's—

ZIERLER: This is systemic, you're saying. It comes from beyond Caltech. Just who's available.

ASIMOW: To a large extent, yes. But not just who's available, but how are we perceived by the candidates that we would like to be applying. If we are perceived as white and male and exclusive and not a place that people are going to feel comfortable, then they don't apply and they don't come. So, it's partly image making. It's partly the critical mass problem. You have to have some students that look like people on campus, or people won't come here to be the only one like themselves, or one of very few. We're so small that the critical mass problem is really hard.

ZIERLER: Is your sense that students of color who are really top-notch are simply not applying? That's sort of a hard thing to know—who's out there, if you don't even know who they are, because they're not applying the first place. But is that a concern?

ASIMOW: Yes, absolutely. They may not be applying. They may be applying and looking us over and not seeing a place for themselves here. I think the heart of Caltech's philosophy is that we want the best students, regardless of their background. We want to diversify the student body and the student experience without sacrificing quality, whatever quality is. The, in my view, indisputably universally agreed upon positive ways to do that are through projecting a welcoming image, through actively searching for diverse candidates and encouraging them to apply, and through yield and recruitment activities. All of those things are uncontroversial compared to the actual admissions decision-making process, where ultimately we want to admit the best students, and we do not want to feel that we are in a position, and we certainly do not want candidates to feel that they are in a position, of being admitted because of their identity rather than because of their preparation or their talent or their promise. So, image, recruitment, yield, finding these students that we want and getting them to apply, and then making sure that we are competitive both financially and socially and in terms of opportunity and academic offerings; that's the best way to build diversity. That is, in my view, what the Institute has been doing. It's more difficult than simply steering the admissions decisions towards explicit quotas or diversity goals, but it works, and it has been working over time, and the pool of applicants has become very, very large lately—for a couple of reasons, but it gives certainly the freshman admissions committee a lot of choices to build and shape a class that reflects society at large.

There seems to be a bit of a runaway, where high school students are applying to more schools, and therefore simply because there are more applications out there, the admissions rates are all going down, so everybody is applying to more schools to make sure they get in somewhere. It's a vicious cycle and there's no brake on it. There's no one willing to say, "No you can't apply to 50 schools. I won't write letters for 50 schools." With the common application, it's too easy. So, not just us but everybody is getting more and more applications every year, even though the number of high school students is stable or declining. Our admit rate used to be—I have records going all the way back to the early 1970s—it was like 10%, 20% of applicants were getting in. And now it's 2%. It's absolutely not a goal of the admissions program to just get more applications in the door, but it certainly helps with diversifying the class, to have a larger pool.

ZIERLER: Even before the language, the lingo of diversity and inclusivity—might be hard to pinpoint the chronology, but do you have a recollection generally of when that sentiment started to become important at the Institute level?

ASIMOW: No. By the time I became involved with admissions which is 2007 or something like that, it was already a core value. It was clear that we were actively looking to move towards gender equity and we were actively looking to build a cohort of underrepresented minorities that would be self-sustaining, and that we were trying to explicitly build a diverse class without compromising on quality standards. That was certainly the philosophy, firmly in place, 15, 16 years ago. I don't know before then, can't speak from authority, but I think once the Institute decided to admit women, it was clear that in the long term, the goal should be to approach gender equity so that the experience would be similar for the men and women on campus. Imbalanced ratios are awkward, and generations of Caltech women could tell you about that more definitively than I could.

ZIERLER: The classes have become more international, also.

ASIMOW: For several years, they became less international. It was up around 15% before 9/11, and then changes in the attractiveness of coming to university in America, changes in the availability of student visas, a number of factors, contributed to a decline down to about I would say a trough of about 8% international students. It has now bounced back. I just saw the numbers for next year's class, and it's like 24% international students or something in the undergrads. It's way above what I thought was the long-term trend. The graduate population has been half international for a long time. At the undergraduate level, there is a sense that, to some extent, part of Caltech's mission is to find and cultivate domestic talent, and that there's a bias towards domestic applicants over international applicants of equal quality. In which case, having such an international class next year suggests that the international applicant pool has just become really strong.

ZIERLER: Do you see that playing directly into the broader impetus toward a more diverse and inclusive campus? Do they work hand in hand?

ASIMOW: [laughs] Operationally, and in reality, international students clearly contribute to diversity. From a federal government and legal standpoint, they don't. There is a category of underrepresented domestic students that is what the federal government statistics are looking at, and international students don't count. [laughs] African versus African American students [laughs]—they're both important, but only one makes Caltech look good on some of the metrics that are used.

ZIERLER: What about Asian American and Asian students?

ASIMOW: That's interesting. It's not an underrepresented minority, and it's also not an aspect of diversity that we struggle to maintain. We have lots of both East Asian and South Asian and Asian American students, and again, we don't need to work to increase our representation of East Asian and South Asian students from most countries. They do come to us, and when they are qualified we admit them. I enjoyed for several years being involved with freshman admissions and helping to maintain this idea that the faculty are at the heart of the process, and it's not just an administrative function. I rotated off freshman admissions when I accepted the charge to be chair of the new GPS Division Diversity, Equity, and Inclusion Committee. That has been my main committee work for the last three years. I should also say before that, I did a stint on the faculty board and on the faculty board steering committee, for three years, which is a good way to make contact with other divisions [laughs] and work with faculty from other divisions on various matters that affect the whole faculty. My main service effort now for three years has been the GPS DEI Committee. That's a very important role, and I've been putting a lot of time and effort into it, to the point where I'm going to do it for a fourth year because it isn't clear who else would do it at this point [laughs]. Obviously 2020 was a very extraordinary year.

ZIERLER: COVID.

ASIMOW: Not only because of the pandemic, but also because of the murder of George Floyd, and a real blossoming in a lot of institutions and a lot of people's hearts of, "Am I part of the problem or can I be part of the solution, and what can we do?" John Grotzinger, our chair, felt this very acutely, and really got out in front of the other divisions and the other Institute leaders in trying to do—something. The GPS Division was the first to start a Diversity, Equity, and Inclusion Committee; now all the divisions have them. Grotzinger realized that if the DEI Committee was going to be able to do anything, they needed funding to back up their initiatives, and so he went around to all of the faculty and he said, "I would like you to contribute $10,000 from your discretionary accounts or your startup accounts to endow a fund for diversity activities in the Division." That was an extraordinary ask.

ZIERLER: That's real money.

ASIMOW: That's real money. There's nothing as valuable as discretionary money to a faculty member, in my opinion—money that you can spend on whatever you want to, without justifying it to a funding agency or writing a proposal for it in advance. It gives you the freedom to do things. Never before or since has anybody asked for contributions like that, that I know of, and never before or since [laughs] has anybody given it. But all the faculty members contributed, so that raised like $400,000. Then the various research centers within the Division contributed from their budgets. With this rather inspirational example of commitment across the whole faculty, the chair and development were able to go to the trustees and the chair's council and outside donors, and say, "The GPS Division is really doing something here," and three substantial gifts came in, like $150,000 gifts, which built this endowment within a few months to over a million dollars. That gives us about $50,000 a year in income to spend on diversity, equity, and inclusion initiatives. There has to be a committee to figure out how to spend that money, but the DEI Committee was charged much more broadly with examining everything that the Division does, and how it does it, and can it do it better in a way that is more consistent with DEI goals.

ZIERLER: What's a great way of spending that $50,000 or a portion of it?

ASIMOW: The bulk of it is spent on what we call GPS Faculty Fellowships, which are $5,000 one-time supplements to first-year graduate students on their first paycheck, which we can use for recruiting students that we especially want in our student body, either because of their identity or because of their commitment to doing DEI work. We can also direct it to students that have special financial need and that wouldn't be able to afford graduate school here without some extra help.

ZIERLER: Because Pasadena is an expensive place to live?

ASIMOW: Yes. Other institutions are competing for these same pool of highly talented highly qualified and also diverse PhD students, so that effort has really helped with our recruiting. It has really helped us to build and maintain a diverse incoming class of graduate students. That's the largest line item. We also can fund outreach efforts like the GO Outdoors program, which is a student-led outdoor education activity that is working with Pasadena Unified School District and other—all the way from elementary through high school age groups around Southern California. We can support them when they need buses or equipment or refreshments or whatever for their activities. We can pay for that. We can pay travel for faculty and students to go to conferences that are focused on networking for underrepresented populations, like SACNAS, the Society for the Advancement of Chicanos and Native Americans in Science, or ABRCMS, which is a biomedical research conference that specifically targets underrepresented students, and various other recruiting efforts, where if we show up and talk to people and invite them to apply, we can make a big difference to the applicant pool. We can host cultural events, where the students from diverse cultures that want to share their festivals or their cuisine or their music with the rest of their colleagues on campus; we can support those kind of activities. We can support SURF students that wouldn't otherwise get summer research opportunities because there isn't funding available.

The rapid increase in the size of the WAVE program has made the summer undergraduate research population suddenly and dramatically much more diverse than it was, but even so, we can with one or two targeted SURFs help the diversity of the GPS undergraduate research population, which is one of the best pipelines to the graduate population. If we have seen a student as a summer undergraduate researcher and we know they're good, we're much more likely to admit them to graduate school and they're much more likely to apply, once they've seen what it's like here. Those are the main things that we can spend money on, but we've done a bunch of other things. A number of the efforts that the DEI Committee embarked on right away, starting in 2020, were pointed out to us in a very forward-looking and broad-thinking and useful document that a group called the Black Students and Engineers of Caltech published in the Summer of 2020. It was a list of demands, but pointed out a bunch of things that the Institute just didn't have on its radar, most notably the Naming and Recognition Committee that Rosenbaum charged to think about whether we should remove the names and likenesses of people that were involved with the Human Betterment Foundation.

ZIERLER: The eugenics movement.

ASIMOW: Yeah. Within the Division, we had a building named for Henry Robinson, who was one of the eugenicists, so the Linde-Robinson Laboratory is now just the Linde Center. Robinson was not actually initially on the radar of that group with Millikan and Chandler and Ruddock. There was more to that document than just the naming question. There were things that were more relevant to divisional operations. We read it very carefully, and a local group of students and postdocs within the GPS Division took that document from the Institute level and pointed out areas in which it applied specifically to what the GPS Division does. From that start, I viewed the best way to run the DEI Committee as a partnership and as a conduit for ideas that come in, often from students or postdocs, and shaping them, given institutional realities, to try to make them happen. We have often I think surprised people with our willingness to listen and our willingness to make changes, and the speed at which we can move and shift the culture. So, the last three years have been pretty busy, in terms of work on mentoring, work on recognizing outreach activities as a legitimate thing for PhD students to do, work on accessibility, work on making sure that there are reporting conduits in place when people do encounter things that make them uncomfortable. It has been a busy time. It's going to slow down a little bit, because we've done all the easy stuff.

ZIERLER: You mentioned the renaming committee in the context of 2020 and the murder of George Floyd. From the origins of the petition to rename campus assets to the way Caltech studied the issue and ultimately responded to it, what did you learn about Caltech, or what did that process make you think that you might not have thought otherwise?

ASIMOW: There were some awkward things about the process. Some of the student leaders lost patience with it, or lost patience with people that were on the committee that were asking questions to learn and understand, rather than just accept what seemed obvious to the students that started the movement.

ZIERLER: This is a classic generational issue.

ASIMOW: Yeah. So the process was a little bit awkward, but I think that the outcome was correct. I think that Caltech knows what its values are, and is willing, in an appropriately deliberative way, to put those values into practice. So, yes, Millikan was a very important physicist, and yes, he was incredibly important in building this institution into what it is, and he does not represent the current values of the institution, and so, it is appropriate to remove his name and likeness, and move on.

ZIERLER: Were you aware, as a graduate student, as a junior faculty member, of the eugenics issue, of the Human Betterment issue? As a Jewish person, were you aware of Caltech's aspects of anti-Semitism in its past?

ASIMOW: No, no.

ZIERLER: That was all ancient history, unknown to you?

ASIMOW: Right. When I arrived in 1991, Sam Epstein walked up to me and said, "Are you Jewish? [laughs] Cool. Welcome."

ZIERLER: That was all the inclusivity you needed right there.

ASIMOW: Right. There were enough Jewish faculty members that were welcoming, explicitly welcoming to Jewish students. I was not aware of that history and it didn't influence my experience at Caltech at all.

ZIERLER: One nuance in the report—you mentioned how Millikan's values aren't consistent with our own—one of the things the report emphasizes is that eugenics was known to be junk science in his own time, so we don't even need to transport contemporary values back in time. I wonder if that spoke to you in particular.

ASIMOW: Absolutely. Yes. It's evidence that he had blind spots and gaps in the rigor of his analysis, according to his personal predilections and biases.

ZIERLER: What about, as I'm sure you've heard expressed, particularly among senior faculty, senior members of the larger Caltech community, this is cancel culture, and who's to say that what we do right now might be perceived in some future generation as unacceptable, and then our name will come off a building. What's an effective counter to that, or should there be?

ASIMOW: No. [laughs] That's okay. That sounds like an invitation to examine what you believe and your values and whether you think they'll be perpetual or not. No, I'm not bothered by that. I think it was the right choice.

ZIERLER: Moving the academic service story right up to the present, when we broke last time, you were on the way to a meeting that was chaired by Professor Michelle Effros about a new curriculum initiative. Can you tell me a little bit about that?

ASIMOW: It's very preliminary. I'm not sure it gets read into the Heritage Project until it happens, but an enormous part of the Caltech undergraduate experience is the core curriculum. It always has been. It is also a source of the number of the problems with the undergraduate experience, and the undergraduate malaise to the extent that there is one. The core curriculum has evolved, gradually, through several reforms over the years, but parts of it are very ingrained and very slow-moving. Michelle Effros, who is the vice provost for Education, has convened an interested group of faculty to test—to develop and then run an alternative core. We are trying to start from a non-canonical perspective, instead of the usual approach which is Caltech students need to know a certain amount of math, and they need to know a certain amount of physics, and they need to know a certain amount of chemistry, and they need to know a certain amount of biology, and they need to know a certain amount of humanities and social sciences, and those things are taught by the various divisions and departments in silos. The Math Department teaches the math core, and the Physics Department teaches the physics core, and the Chemistry teaches the chemistry core, and there's very little interaction between them. We're starting from the perspective of an integrated core. We are designing a class that we are provisionally calling Science 1. The faculty that are involved in the effort are from currently almost all of the divisions. We don't have a chemist yet, and we need one. But Rob Phillips, who is himself a very broad and interesting and iconoclastic and difficult-to-classify scientist on the line between physics and biology—

ZIERLER: One who never really went to college, on top of everything else. [laughs]

ASIMOW: He's really the leading mind behind this effort at this point. I'm there because I've been teaching GE 1, the menu class, and successfully engaging large numbers of students, and getting them outdoors, to add that to their educational experience. If we're starting from scratch and designing an entirely new core curriculum, we can build in as much field component as we want, as well as lab component, and projects, and efforts. I'm really interested in this. Glen George is there, from Electrical Engineering, and we just got Tom Graber from Math to join the group. There was a first meeting with a lot of senior people—the provost was there; Carver Mead was there—where we all agreed that a bold experiment is timely. Part of the question is, we're aiming to have this ready to go in the Fall of 2024 for a group of 24 students.

ZIERLER: By invitation only? Self-selected?

ASIMOW: We will see [laughs] what the selection process ends up being. Certainly there should be an element of application and of selection, but we don't quite know what the selection criteria are.

ZIERLER: This might be redundant, but is this something like a gifted program?

ASIMOW: I don't think it should be.

ZIERLER: The way I should put this is, obviously you're going to want students who will thrive in this new kind of environment. Nobody should be built toward failure. Doesn't that by definition mean that it's going to take a very—I mean, all Caltech students are strong—but strong among the strong? Or, no? Or, needs to be more of a cross-section, to see if it works?

ZIERLER: I don't think strength is the criterion. I think the criterion is curiosity, and willingness to experiment, and eagerness to participate and carry your weight in group projects. Basically there is a sense amongst the faculty that Caltech students come in curious, and broadly interested, and excited about science, and/or engineering, and by the end of freshman year, the light has gone out of their eyes, and they're just doing problem sets, week to week. That feels like a tragedy, like we're doing a disservice, to turn excited 18-year-olds into bored 19-year-olds, overworked 19-year-olds, frustrated 19-year-olds. That's the goal of this effort, is to [phone ringing]—Caltech is calling; it's probably a drill. I won't answer. [laughs]

ZIERLER: Me, too.

ASIMOW: [laughs] Maybe it's a shelter in place command, but it's probably a drill. So, no, the idea is even within our generally overall small student to faculty ratio, to even further optimize the face time that these students are going to get with faculty. To approach every question from an integrated and fundamental perspective and not to teach material just because we've always taught it, or we think they're going to need it, in the future. Teach them what they need to know now. The best example module, the one that Rob brought up first, we're going to start the class with the idea of diffusion as a unifying principle across math, physics, chemistry, biology, Earth science, what have you. We said to Tom Graber, the Math professor, "Can you teach a group of students what they need to know about the diffusion equation"—which is a second-order partial differential equation—"if they haven't been slogged through ordinary differential equations and all the traditional things that lead up to it? How would you go about that? Think about it." The same thing from a physical perspective, from the chemical perspective, from the biological perspective, from the Earth science perspective. Diffusion is important in all these fields, and can you teach in a rigorous way what diffusion is, and why it's important, and how it works, to students that haven't gone through the traditional canonical approach to all of the subfields? We'll see.

ZIERLER: Is the goal to expand the pilot program of 24 to—the undergraduate program? To replace ultimately the core curriculum with this, if it works?

ASIMOW: That is one possibility. Certainly we are aware that the experiment will—assuming the experiment gets approved, because it has to go through the core curriculum steering committee, which I accepted a seat on so that I can help [pause] push this thing through.

ZIERLER: Ah, there's an inside man! [laughs]

ASIMOW: [laughs] Yes. Assuming it happens, certainly we know it will be watched, by the other students, by the other faculty that are teaching the traditional core. The answer to people that say, "We don't believe it will work," or "This seems fluffy," or "This isn't consistent with the way Caltech has always done things," we're going to say, "This is an experiment. Meet these 24 students when they are alums of this program, and you decide, are they ready for the advanced curriculum? Are they the students you want in your lab? Or are they not?" We'll see. I asked the question at the last meeting, "Do we want to think from the beginning about whether what we are doing is scalable?" Whether the effort per student is such that we could run the same program ten times larger. Or, should we just focus on doing it right for 24 students and think about scaling it later? I think the answer is, "Think about scaling it later." Maybe it will always be a small, alternative cohort within the larger Caltech program. Hopefully, if it is that, it will influence the way the rest of the core is taught, that it will move in more interesting and creative directions. Or, it will be one of many versions of the core. Instead of Science 1 and traditional core for 24 students and for 220 students, maybe there will be multiple—I don't know what to call them exactly—academic tracks that satisfy the core requirement.

ZIERLER: Because the possibilities are so profound of changing Caltech's undergraduate curriculum, what level of buy-in is required beyond the core curriculum committee? Does the provost need to sign off? The president? The Board of Trustees? How high does this go?

ASIMOW: [laughs]

ZIERLER: Or is it really a case of just how powerful faculty are at Caltech.

ZIERLER: That's right. It is entirely within the purview of the core curriculum steering committee to do this. Of course, the core curriculum steering committee is a subcommittee of the faculty board, so likely, it would come before the faculty board. The provost has already given an imprimatur by either allowing or encouraging the vice provost to start this planning process and by coming to the first meetings of the group. The president's job will be to find a way to spin this to the public and the trustees and the development initiative so that it contributes to the sense that Caltech is interested in the future of undergraduate education and is working in a manner consistent with its mission statement and doing something exciting and new.

ZIERLER: The metanarrative here, obviously, is that science is becoming more interdisciplinary. That's just where everything is headed. To what extent is the real story here about computation, that computation is the merge point of all of these disciplines?

ASIMOW: That will be potentially one of the themes of this integrated curriculum; it will not be the main theme.

ZIERLER: Do you also see it as a way to manage the undergraduate imbalance, interest in computer science?

ASIMOW: Yes.

ZIERLER: That yes, they want to do computer science, but then you can bounce them back to, look what you can do with computers in Earth science and biology and chemistry and physics.

ASIMOW: Right. Ultimately, if Caltech is going to continue to do anything like what it does, that is necessary. Otherwise, what is the point of making the computer science students take the core? It's just a wasted year of their life that, because you want to go to Caltech for whatever reason, you need to take this much physics and this much chemistry and this much math, and then you can go be a computer scientist. That just doesn't seem like it makes anybody happy. Yes, the way for Caltech to continue to be what it is and what it has been, and to serve students where they are and where they want to go, which is recognizing that there are many careers in computer science broadly, and that computation is an increasingly powerful approach to many problems, is to make sure that we are exposing the students that are going to be computer scientists to the breadth of things you can do with computers—

ZIERLER: Beyond just coding for a tech company.

ASIMOW: Yeah. In a way, that's already true, but it's not clear that the students realize that. Students that just want to code—

ZIERLER: First of all, they might be starting to get concerned that coding is going to be one of those things that is overtaken by AI.

ASIMOW: Yeah, that's the next wave, the next problem that we have to deal with. But currently, the computer science major at Caltech is a very particular thing within the larger field of computer-related activities. It's very theoretically bent. It's very oriented towards the ideas of what is a computer, what can a computer be, rather than how do you use computers as they are. It's not obvious to me that the incoming students that are coming here because we're Caltech and they want that name on their degree and they want to be computer scientists are actually paying enough attention to what Caltech computer science is, and that leads to a considerable dissatisfaction at some point. But yes, for me, trying to justify my existence here and trying to engage with the students, and trying to educate them in a way that feels valuable and important to me, certainly ensuring that there are connections between science and engineering, and between mathematics and computing and science and engineering and all these areas, as an integrated way of approaching problems—yeah, that's important. We'll see where it goes!

ZIERLER: Let's shift now back to science, your science. When in the narrative for you does JPL start to really become an important part of what you do? Is it gradual? Is there a particular mission? Is it a graduate student that pulls you in? What's the thing that happens?

ASIMOW: I have to challenge the foundation of the question: JPL is not really an important part of what I do. It's an element, among several. It has never really been, it is not yet, and it may never become really critical to my program.

ZIERLER: I could repurpose that. Because I know you do stuff, by definition—because the demands on your time are so important, it has to be important, even if it's a very narrow slice of the pie. If it wasn't important, you wouldn't do it at all, because there's something else that would take up that slot.

ASIMOW: Yeah, okay. I visited JPL before I ever visited Caltech, because my undergraduate research was based on the Magellan mission to Venus, and I was there at JPL for orbit insertion in August of 1990. Then when I got here for graduate school, I felt that the planetary NASA mission-based community was really pushing me out, and I let myself be pushed out, and moved into strictly terrestrial work for a long time, and had no connection with JPL during graduate school. Then I started, once I was here on the faculty and I had my lab up and running, interacting with some of the technology groups at JPL, and in particular the thermoelectrics group. That's one of the groups at JPL that are developing basic technologies that may be useful for spacecraft and may be useful for other things. That's one of the things that JPL does other than just launch spacecraft, and build spacecraft and launch them and operate them; they have all these technology groups. The thermoelectrics group there—a thermoelectric is a material that takes advantage of a second-order coupling between temperature gradients and electrical potential, or electrical potential gradients and heat transport. When you put a thermoelectric material in a temperature gradient, it generates a voltage. Conversely when you apply a voltage to it, it transports heat. One of those is called the thermoelectric effect, while the other one is called the Peltier effect, and both of those are useful.

The way that a radioisotope thermoelectric generator works, which is how many spacecraft are powered, is plutonium keeps itself hot, space is cold, so you have a rod of plutonium, and naturally there's a temperature gradient around it, and you fill that space with thermoelectric material to generate voltages. Or, if you need to keep let's say an infrared sensor for a telescope cold to reduce thermal noise, you can just apply a voltage to a Peltier element and it cools itself down, passively. You don't need a coolant. Those are both useful. Both of those properties can be optimized by suitable choice of materials that have very high Seebeck coefficients, which is the ratio—or the voltage difference divided by the temperature difference—that have a very high electrical conductivity, so you don't waste all your power just conducting across the thermoelectric material, and a very low thermal conductivity so that you don't waste all your heat just bleeding through the thermoelectric material. Generally speaking, electrical conductivity and thermal conductivity are correlated with each other, especially in metals, so it's a challenge to find a material that has high electrical conductivity and low thermal conductivity.

There was a group here in Materials Science, Sossina Haile's group, working with people up at JPL on optimizing thermoelectric materials, and they realized that some materials that you could synthesize at high pressure might be promising candidates for better thermoelectrics. They started coming to me to do experiments in my lab where I could synthesize these materials at high pressure. This was one of those examples of things where "I have a machine, I have spare time on the machine, this is an interesting problem, let's work together." I did that. Then the PhD student that was working on that project didn't get along with his advisor in Materials Science and he came to me and said, "Will you be my advisor?" So I found myself PhD advisor to a materials science student working on thermoelectric materials in my lab. Okay. So, there was some connection to JPL there, and that was the first point of connection that I can remember. Then, they hired a petrologist who works on meteorites and planetary surfaces named Yang Liu, who is also a visiting associate here at Caltech and is kind of our point of contact in petrology and meteoritics, and I've collaborated with Yang on a number of things over the years.

Most recently, there are groups at JPL that are interested in outer solar system processes and high-velocity collisions among ice particles. Part of this is planning for a mission to Enceladus. Part of this is just thinking about what—an instrument that happens to be on the Cassini spacecraft that was flying around in the Saturn system for many years, what that data mean. I have this shock wave lab where I can crash things together, including ice and whatnot, and so I've been collaborating with some groups up at JPL on these outer solar system and hypervelocity and ice problems.

ZIERLER: It sounds like what you're saying—you're more of a service provider. You have capabilities that are useful for things that are not at the core of your own interests.

ASIMOW: For the most part, yeah. Most recently they had a machine called the hypervelocity ice grain system, and it lost its space at JPL, and they asked if they could move it down here into my space. I'm like, "Okay. I have space." [laughs]

Future Possibilities on Venus

ZIERLER: It's amazing to think that space is more at a premium there than here. It's an enormous place, JPL.

ASIMOW: That is true. Also, I met a bunch of them through a KISS study project—Keck Instrument for Space Science. I participated last year in a study project looking at the possibility of a really new mission architecture for studying Venus of putting a long-lived lab on a balloon in the middle of Venus atmosphere, as a compromise between the very difficult alternatives of bringing samples from Venus back to Earth, or doing work in situ on the surface of Venus.

ZIERLER: Which is impossibly hot.

ASIMOW: Impossibly hot, right. JPL is working on hot technology—machines, computers, electronics, that would work long-term at Venus surface conditions—and that's one direction you can go in. Certainly geochemists always love sample return. We really are good at doing things here in clean labs with big expensive very heavy machines. The question is, is there a space in between right now for a mission that would get around the challenges of working at the surface, and get around the challenges of getting samples back to Earth, by taking advantage of the fact that 50 kilometers up in the Venus atmosphere, the temperature is like the surface of the Earth, and the pressure is like the surface of the Earth. It's a little bit acidic, but it's pretty Earthlike. We have machines that work under those conditions. There are some measurements that you just can't make quickly. Going all the way back to the 1970s, the Soviet Union was pretty good at landing spacecraft on the surface of Venus and making measurements for about half an hour before the spacecraft got fried. But there are some things you just can't do in half an hour. We've seen this with the Mars rover. They will sometimes drive up to a rock and park there for days, to do justice to that rock, and use some of these flight-capable instruments that are only able to generate a relatively weak signal, and therefore they have to count it for a very long time.

This was a pretty blue-sky concept. First of all, you have to work out how you are going to get an aerial lab on a balloon and how long it could live in the middle Venus atmosphere. How are you going to get down to the surface? How are you going to sample the surface and get the rocks back up? How are you going to rendezvous with the aerial lab? A lot of architectural level questions. But what KISS does is take the engineers who are good at thinking about these architectures, together with the scientists who have some idea of what problems need to be solved and what measurements need to be made, and just—talk, for a week, and then get back together again and talk for another week. I don't know that this mission will ever fly, but it was interesting to meet some of the people from the spacecraft engineering side at JPL, and the mission planning side, and also the planetary science side, and see what we could come up with.

ZIERLER: Because your interests are primarily terrestrial, Earth-based, when is it valuable just to be aware of what's going on beyond Earth? For your interests on Earth.

ASIMOW: Earth is a planet. It's a very interesting planet, but it's just one. It is inherently interesting to ask why the Earth is the way it is, and you can't get very far with an N of 1. You need to see alternative pathways, planets that have gone other directions, to know what else is possible, and then try to identify, what's the branch point where a planet goes down one path or another. That is the way that I wrote the justification for this Venus mission, is, what are the possible branch points that explain how Earth got locked into the Earth evolutionary track, and Venus got locked into the Venus evolutionary track? If you want, you can also think about Mars. Earth has been walking down this very finely balanced middle road of habitability. It's neither too hot nor too cold. It's the Goldilocks Zone. Mars we think was once habitable but it went cold death. I don't know if Venus was ever habitable, but if it did, it went hot death. Why? Was this already foreordained by the planetary building blocks from which Venus and Earth were made? Or does this result from the giant impact stage of accretion? Or does this result from the evolution of the early atmosphere? Or is this something that happened slowly over time due to the loss of the magnetic field when Venus's core stopped its dynamo, if it ever had a dynamo? We know that Mars did, but we don't know that Venus did.

There are lots of possibilities. Once a planet gets into a strange attractor, it can stay there for a very long time, and so you need to find the points where it decides which of those attractors to get attracted to. That tells you a lot about the Earth. If you just look at the Earth, it's easy to think that it's obvious that planets should work this way. It's very hard for terrestrial geologists to imagine the Earth without plate tectonics. Yet, it's the only planet we know of that has plate tectonics, and you need to look at other planets to really get that perspective. We have a small sample of planets here in the solar system. We have a much larger sample of planets beyond the solar system, but limited information about them.

ZIERLER: Do you think ultimately we'll learn enough about exoplanets where they will be interesting to you from a geological perspective, or is that technology too far out?

ASIMOW: No, it's not too far out. We're already learning things about them, and the pace of discovery there will continue to accelerate, I think.

ZIERLER: We just need to get the TMT built.

ASIMOW: [laughs] Somewhere. Or there's going to be a 30-meter class telescope in the Southern Hemisphere, that Caltech is not involved in, that will not accrue glory to Caltech but it will address those kinds [laughs] of science problems, for at least half of the sky.

ZIERLER: Let's move the conversation close to the present. I know there's so many things you're involved in right now, but to go back to this idea of those bored 19-year-olds, what are the things that you're working on now that are really exciting to you, that's not all the stuff that you have to do? What's going on that's keeping it interesting and new?

ASIMOW: The quasicrystal enterprise is endlessly fascinating and bizarre. I don't know if you've come across any of this.

ZIERLER: This is like the Paul Steinhardt and Eastern Europe saga?

ASIMOW: Yes, that is part of it.

ZIERLER: Rob Phillips, also.

ASIMOW: Has he been involved?

ZIERLER: He has been involved with quasicrystals.

ASIMOW: Caltech has a checkered history with quasicrystals because Paul Steinhardt, who is a Caltech alum, basically figured out what they are, but Linus Pauling, for his whole life, insisted that they weren't real and kept trying to find new kinds of twinning that could explain the patterns that were observed without breaking the rules of traditional crystallography. I got involved—well, Caltech got involved again with quasicrystals after the natural ones were found by Luca Bindi and Paul Steinhardt, and they realized that they might be extraterrestrial. They came to John Eiler to do oxygen isotope analyses, which are one of the ways of recognizing whether something is of the Earth or not. Then I don't even remember how the first contact was made, but the Princeton group, Lincoln Hollister, also a Caltech alum, studying the fragments that they recovered from the Khatyrka meteorite, noticed high-pressure minerals, the kinds of things that are made by impacts.

I happened to have been doing shock recovery experiments, where I put a mineral sample in a metal capsule and drive a shock wave through it, and then recover it, cut it open, and see what you get, and I had noticed melting at the interface between the metal and the minerals, and mixing of them and droplets of metal suspended in the quenched mineral glass, and droplets of mineral glass entrained into the molten and frozen metal plumes. We were studying these experiments for a completely different reason when I saw the texture at the interface between the quasicrystals and the other components of the Khatyrka meteorite that looked just like my shock experiments. And so, very quickly I got into conversation with Paul and Luca, and we decided we would test the hypothesis that the reason there are quasicrystals in the Khatyrka meteorite is that they were synthesized by a shock wave, following upon a collision in the Asteroid Belt. It seemed like a real fishing expedition. Quasicrystals are rare. Metallurgists only discovered them in the 1980s and only make them by very carefully controlled cooling rates applied to very particular compositions of very pure alloys. But we put a bunch of stuff in one of my shock recovery chambers, and we shocked it, and the first time we tried it, we made quasicrystals.

ZIERLER: Meaning that it's not so hard for the universe to make these things.

ASIMOW: Right, in transient energetic events. The first time we did it, it worked. The second, third, and fourth times we did it, it worked. I had an incredibly successful SURF student, Jules Oppenheim, who got two first-author papers out of one SURF project based on two experiments, each of which yielded a new kind of quasicrystal. [laughs]

ZIERLER: Wow!

ASIMOW: Best SURF ever. We really showed that if you have the right starting materials, the passage of a shock wave and a transient high-pressure, high-temperature event can nucleate and grow significant sized quasicrystal domains, and that's almost certainly why they're there, in the meteorite. We've since built on that to look at other transient high-energy events. Luca Bindi found a quasicrystal, a completely new one, a calcium silicon copper quasicrystal, in a piece of red trinitite. Trinitite is glass that was formed by the first nuclear test, the Trinity test, in Alamogordo, New Mexico, on July 16th, 1945. That made quasicrystals, at least one. We've been following up on that, trying to see if we can synthesize that quasicrystal, if we can find more of them in the trinitite, if we can simulate the growth of that quasicrystal. I had another SURF student who worked on all of those angles, of searching through the trinitite for more quasicrystals, doing shock recovery experiments to see if we could make that quasicrystal, and also learning to do molecular dynamics simulations of quasicrystal forming systems. She is now a PhD student at Princeton doing molecular dynamics simulations. That was a successful SURF inasmuch as it guided her to a research career, although we didn't actually find or make any quasicrystals in that summer.

ZIERLER: Are there industrial applications at play here at all? Is there a demand for quasicrystals?

ASIMOW: The only commercial application that has reached the market is nonstick coatings made of quasicrystalline material. They have useful surface properties. It's not clear that they are competitive with ceramic coatings, which already have nonstick properties that go to higher temperature than Teflon. But that's one possibility. They may well have applications similar to bulk metallic glasses, which Bill Johnson over in Materials Science kind of really is the leading developer of that field, and they've commercialized some of those products for making golf club heads that have much lower acoustic loss than any traditional metallic alloy. They have some things in common with bulk metallic glasses. I've been studying them just because they're weird, and it's a curiosity, and I'm interested in that, and that's what you asked. [laughs]

ZIERLER: That's fundamental research. That's what it is.

ASIMOW: We've also found quasicrystals in fulgurite. Fulgurites are fused rocks that are made by lightning strikes or electrical discharges. There's one from a place called Sand Hills in Nebraska, and it's not clear whether—there is a downed power line associated with it, but there may also have been a lightning strike. Anyway, there's a quasicrystal in that stuff; that just came out. It was just remarkable how easy these shock syntheses of quasicrystals have been, and that has kept me active and collaborating with Paul Steinhardt and Luca Binda and others on the whole natural quasicrystal story. We just submitted a paper yesterday on another instance of copper aluminum alloys from an extraterrestrial object. Up until now, Khatyrka is the only one, which makes it legitimate to question whether it's really extraterrestrial, if it's a unique object, especially if it comes from Russia. [laughs] There's a lot of suspicious skullduggery associated with specimens coming out of Russia. But this is a micrometeorite, a spherule, that was found in the Nubian Desert in Sudan, not coming from Russia at all. It doesn't have any quasicrystals in it, but it has copper aluminum alloys.

We did a transmission electron microscope study of the crystallography at very small scale; it contains two of the same minerals as Khatyrka, plus potentially a new one, a new copper alloy composition that has not been seen in nature before. We haven't characterized it well enough to name it as a mineral yet, but we're going to try. That has been one thing that I have really been enjoying doing, is playing with quasicrystals. I led the writing of a proposal a few years ago to buy a new electron microprobe that has much higher spatial resolution than our previous electron microprobe. That proposal is funded, in part because the second time we tried it, the proposal had a very strong broader impact statement. NSF proposals these days need to justify both their intellectual merit and their broader impacts. In the last few years, the broader impact requirement has really started to bite. It has been in there as part of NSF proposals for years, but panels and reviewers weren't really paying it very much mind, and it never made the difference to whether a proposal was funded.

ZIERLER: Broader impact to translation, or broader impact meaning this will affect fundamental research? Or both?

ASIMOW: Anything that is not just—

ZIERLER: You can't just say, "This is interesting to me and my lab."

ASIMOW: Right. It can be outreach. It can be mentoring. It can be education. It can be community science. It can be translation. It can be collaborating with wildly different fields. Something that makes your work potentially relevant to somebody other than the people who were already interested in it. We joined a consortium known as the Remotely Accessible Instruments in Nanotechnology, or RAIN, network, that maintains a list of research-class instruments that can be operated remotely by anybody with an internet connection. We offer sessions to high school classes, or high school researchers, or public libraries, or whoever wants to get a group of typically young people, or people in technician education programs or whatever, get them together to see how one of these instruments actually works and operate it. Our electron probe is the only electron probe in the network, and I think that made the difference between us getting one and everybody else who wants one getting one. Over the last year, I've been learning to use this new electron probe and see what it can do, and how it's different from the old one. That has been exciting just because it's a new toy. Also, going to new places, and working on the rocks and seeing what you can discover. The Baffin Island expedition and all that followed from that, that was exciting. The Cameroon expedition and what is following from it is occupying a bunch of my time now.

I've been teaching GE 1 now for 11 years, and it's getting, for me at least, a little stale. It's a good class and I love doing it, but the integrated core curriculum effort will take me away from it. If I teach Science 1, I will not teach GE 1. That's an opportunity to do a major refresh of my teaching skills and class design. I designed GE 1 eleven years ago, and I'm still basically running it the same way. Every now and then it's good to build from scratch and do something new. One of the ways that I have always done that is my graduate seminar level class, GE 215. The description in the catalog basically says, "We'll figure out what we're going to do." The way I run that class is on the first day, I hand out eight or ten potential syllabi and I let the students vote on which one they want to do, or even propose a new one and then I sketch it out as a syllabus and put it into the election. I have been teaching that class every two years since about 2008, and three of those times, I have made the class up on the fly. The students came up with a new idea, they voted on it, they chose it, and I said, "Okay, let's do it." [Laughs] That's challenging, but that's fun and exciting. That's actually what I won the Feynman Prize for. It was not teaching GE 1 or any big class, or any required class; it was for a group of maybe six or eight graduate students making up the class that they wanted to do in real time. I do that every two years, and sometimes it's new, and sometimes it's old. The version of the class that I always want to do is the Thomson phase equilibria curricula, teaching from Ed's notes, but it's pretty hard to talk the students into [laughs] doing that. That's another thing that I wish that I had more time to work on, is the book that Ed and I are writing, because I love that material and I would like to be spending more time with it. But there are so many other distractions.

Back to tvop

Reflecting on the Big Questions

ZIERLER: Now that we've worked right up to the present, to wrap up this talk, I want to ask a few broadly retrospective questions, and then we'll end looking to the future. Mentorship—I know mentorship is so important to you. What have you learned about being a mentor, both to undergraduates and to graduate students? What's the platonic ideal that you aspire toward, based on your experiences?

ASIMOW: A student who is unaware of their own potential coming to see it and discover it and live in it and pursue it. Students that come in fully formed and they know their strengths and they know their potential and everybody recognizes them and I just say "go" and they go; that's easy, and great, and good work gets done, but at some level anybody could have mentored that student. Students that need constant attention and are always going to need constant attention and don't really get to the point of self-starting, that's kind of a fail. It's less of a fail than a student that drops out, that you don't pay enough attention to when they needed the attention, and they didn't get it. There is somewhere there the possibility of a student that can start their motor and then run with it and realize what they can do and go and do it, and that's the best kind of mentoring experience. I've only had that a few times.

I had a SURF student who was a fairly recent refugee from Syria, came to me through a program that JPL had organized, where they were taking one student from each community college, and getting them a SURF, and getting them some internship opportunities. I had this student one summer, and he really had very little confidence in himself, didn't really know why he was here. I had him back a second summer, and it was a much better experience. He has gone on to have a very successful career, and when Syria completely fell apart I was really glad that he was here and not there. That was meaningful for me, was really putting in the time and investment in this student who didn't really believe in himself at first, until after a couple summers of working here with me, he really did have what it took to get up and get going.

ZIERLER: Technology. What's an example of a technology that has been a real game-changer in the course of your career? What technologies are real workhorses that were with you as a graduate student that are just as useful today?

ASIMOW: Computing is a major one, and it gets faster with time, and that allows us to do more calculations more quickly. I haven't reached the singularity where suddenly everything can be computed so fast that there's no point in doing anything else, but computing has been important really all the way through my research effort, just because thermodynamics is a nice principle but doing anything practical with it requires the ability to quickly solve a whole bunch of equations and minimize functions. That has always been important. The experiments that I do depend on pretty brute force basic mechanical engineering of hydraulic presses or blowing up gunpowder, but the analytical tools that we apply to what we recover from those experiments—the microbeam technologies and the ability to analyze things at smaller and smaller scales—that has been critical. The field emission electron source was the revolution that came through scanning electron microscopy and most recently electron probes, allowing you to get down from micron scale to near nanoscale; that has been very valuable. Because a lot of things are very small [laughs], and when you can look at them at those small scales, you can see and learn new things that were really hard to learn before.

ZIERLER: Two more. Leadership. Your commitment to service at the Division, at the Institute. Are you satisfied that all of the change that you want to see happen, you can do from your perch as a Caltech professor? Or is there a future where being a division chair, or an assistant vice president, or something like that, is really required for you to do the things that you want to do?

ASIMOW: No, I have no ambition to higher leadership positions.

ZIERLER: Which is the first requirement for becoming [laughs]—the leadership.

ASIMOW: Unfortunately, yes, it's not out of the question that I will end up being the next division chair. I don't really want to, and I will have to stop and think about what my vision is and whether everyone shares it, if we come to that. No. I have enjoyed being able to move things forwards just by making connections, by knowing who to talk to and working behind the scenes. I like that mode. So, no, I don't especially intend to seek more responsibility or more leadership. But I recognize that it may come to me.

ZIERLER: [laughs] Finally, Paul—knowledge. If you put together all of the papers, all of the students, all of the lab work, all the curiosity, what does the field know now, what do you know now, that was unknown when you started in this business?

ASIMOW: There's a lot of little things. There's just a couple of big things.

ZIERLER: That's what I'm after; the big things.

ASIMOW: To me, the biggest thing is still the whole thermodynamic modeling initiative as a way to understand igneous rocks, that came out of my thesis work, and is still rolling along, and in particular the recognition that pressure and temperature aren't always the independent variables, and you have to be able to think about approach to equilibrium using non-traditional constraints. It's still a challenging idea but it's really important, and it's the basis of kind of everything that I have done with mantle melting. On the high pressure and mineral physics and melt physics and shock wave side, the understanding of the uniqueness of the behavior of liquids compared to other materials is the main discovery that I can point to and that I'm still exploring the consequences of. Those are the two biggest things.

ZIERLER: I want to thank you for spending all this time with me. I had a fantastic time. We covered so much. I really appreciate it.

ASIMOW: Thank you for your insightful questions. I'm impressed with your homework! [laughs] To figure out which questions to ask.

ZIERLER: Absolutely.

[END]