Episode 6 Transcript: Earth's Vital Signs

Introduction (00:03): Great science and engineering often begin with a singular hypothesis, but how does a lone spark of innovation become popular science? From Caltech, this is The Lonely Idea.

Rich Wolf, host (00:16): This is your host Rich Wolf. In this episode I'm talking with geologist and geochemist, John Eiler. John is best known for his innovative work in clumped isotope geochemistry, which among other things has given us insights about the body temperatures of dinosaurs. John, welcome to The Lonely Idea.

John Eiler, guest (00:32): Thank you very much, Rich. I'm glad to be here.

Wolf (00:35): John, before we get talking a bit about clumped isotope geochemistry, maybe you could talk a bit about how you got into the field of geochemistry and earth science in general and your background.

Eiler (00:44): So I started my academic career by getting rejected from every college I applied to. So, I was originally not going to go to college at all. And then my dad got on the phone and talked me into an institution called Beloit College, which is a little ACM [Associated Colleges of the Midwest] liberal arts college in the Midwest, which is where I grew up in Madison, Wisconsin. And I went there to study not really much of anything. I went there to be at college and lift weights and hang out with friends and things like that. But in the course of fulfilling a science requirement, I took a geology course. Aand the instructor of this geology course, who was a fellow named Hank Woodard, who was an office mate with the famous Jerry Wasserberg, one of our illustrious colleagues. And he figured out somehow that I knew how to fish and I was big enough to carry stuff and things like that. And so he hired me as his personal porter for field excursions. And I spent several field seasons going into Southern Canada and hauling around his canoe and hauling around packs and cooking for everybody and fishing and stuff like that. Eventually I sort of fell in to that social group and that was how I became a geology major. And it just sorta stuck. I just kept doing it.

Wolf (02:10): And, you didn't have a particular fascination with science, but that grew as a function of this relationship?

Eiler (02:15): No, I was always really fascinated with history. I wanted to be a history major, but I got a C in my first history class and so I kind of slid out of that. And then I wanted to be an anthropology major, which remains a fascination of mine. If I'm at home, I'm probably reading, and if I'm reading, I'm probably reading history or prehistory, anthropology. So, it's something that I'm fascinated by and it felt like a short step to be in the earth sciences, which are very historical in their worldview. I just was lucky enough to be good at it. I was just good at it. So I kept doing it.

Wolf (02:56): And you went from there to the University of Iowa.

Eiler (02:58): Right. While I was a freshmen at Beloit, I met my wife to be, and she was on her way out the door. She didn't really like Beloit College. She wanted to transfer to the University of Iowa for various reasons. She was interested in women's history and they're very good at that. So she was leaving. We recently figured out that all of this occurred over a span of like six weeks. I met her, went on our first date, and then six weeks later or so she left the college and I followed her. I went to the University of Iowa for us to be together and we're still together. When I was at Iowa is when I started becoming serious about academics. And I just decided one day, you know, I'm going to do this. I'll see if I can be good at this. And it was fun, engaging, and I discovered you'd get rewards for these things if you get good at them. And so I kept going and wormed my way into it.

Wolf (03:52): Now I know serendipity is going to be a theme throughout this. I'm already picking up on that. But this concept of history being a guide for you, we're going to come to that in a second, because it was a knowledge of the history of geochemistry and some experiments that had been tried decades before that brought you to develop clumped isotope chemical methods. But maybe before we get into that, let's level set with our entire audience and explain in lay terms what is clumped isotope geochemistry.

Eiler (04:20): So, the word isotope is a made up word, [and] means "same place." It means same place in the periodic table. And it was coined after the discovery that there were different versions of the chemical elements. There were the common versions that had an atomic mass near what you would weigh if you just concentrated that element into a lump of metal and weighed it and figured out how many atoms were there. And then there were rare versions that were slightly different in mass--the isotopes--and what they represent are versions of that chemical element that share the same number of protons, the charged particle in the nucleus, therefore they share the same number of electrons, that charge balance the proton. And because of that, they have close to the same chemistry, but they have different numbers of neutrons, which are an uncharged but heavy part of the nucleus.

Wolf (05:15): Many of us and many of our audience listeners are familiar with radio isotopes because we're all knowledgeable about uranium and the bomb and things like that. So we know about radioactive versions of elements, but you're looking at something very different.

Eiler (05:31): That's right. So, some isotopes, if they obtain either way too many or way too few neutrons for the stable configuration of the nucleus, they'll spontaneously decay and break apart. This is not what I study. So that process occurs as a steady beat, like a metronome, and can be used to date things. That's for geochronology or the dating of former events. There are other sorts of isotopes that are somewhat unusual and yet they're stable. They just exist as a kind of background. I think of them as like a shadow court of the periodic table. They are everywhere. They are chemical elements that are just like the ones you know about. But with a teeny little twist. They're slightly different, a slightly different version of carbon, a slightly different version of oxygen or of hydrogen, and they never undergo radioactive decay. They're just there and they become distributed throughout all natural materials, through chemical processes, physical processes. We inherited them when the earth first accreted, they will be here when the earth has its last day, but they're not evenly distributed everywhere. They have been separated from one another throughout Earth history by chemical and physical processes.

Wolf (06:47): And so how does this become clumped isotope geochemistry?

Eiler (06:49): That's right. Okay, so these are the isotopes. So what do I mean by the word clumped? So clumped means I have two rare isotopes. Okay. And they somehow found their way together into a shared chemical bond. They are next to each other and this is an event that can occur randomly in natural materials just by chance. If I have one part in a hundred of an element, say carbon, that is a rare isotope, say carbon 13, then there's a 1% chance that any given atom is going to be carbon 13. What about its neighbor? If it has a neighbor that's carbon, well then there's a 1% chance that it is carbon 13. The probability both are carbon 13--100 times 100--1 part in 10,000. Clumped isotope geochemistry is about studying the differences from that random chance.

Wolf (07:40): And before we talk about what we can do with that, let's go back to Harold Urey, because I think the historical context is so fascinating.

Eiler (07:46): From the modern standpoint, the study of such very rare species seems exotic. It seems [like], how could you ever observe them? They only vary subtly in their proportions. Why would you study them? It's a peculiar thing to study. But if you know the history of the literature, of the discovery of isotopes and the discovery of their chemistry, they were at the very center of people's thinking. They were the most important species in the minds of the first chemist to study isotopes. So the first person who really made a coherent statement about this problem was Harold Urey, who was a chemist who worked at Princeton and the University of Chicago. And he was effectively the teacher of the teachers of everyone who would go on to do all sorts of isotope geochemistry. He taught my postdoctoral supervisor, Sam Epstein. He taught lots of people in this field. And when he was at the height of, or the first blush of, his career was the study of the chemistry of the rare isotopes. And he was basically asking a question about the nature of the chemical bond. People wanted to know, is the chemical bond a quantum mechanical phenomenon or is it a classical mechanical phenomenon?

Eiler (9:06): Urey was fascinated by this as a way of testing the nature of the chemical bond. Does the energy change or does it not? The consequence of this that he was predicting is that if chemical bonds are quantum mechanical in nature, then when I put a heavy isotope in a chemical compound, it will become more stable. And he was fascinated in this. And he was also fascinated in the natural sciences and geochemistry and cosmochemistry and the history of the earth. He was the first person to have this thought, what if I could take the chemical physics of these highly substituted molecules that have multiple rare things in them and apply them to the study of the earth. And he thought about it and he did a few calculations and realized that he would see a very useful phenomena, like temperature-dependent phenomena that could be used to establish climatic temperature in the past. But he'd realized they'll be very rare, no one would ever observe things--if I have a rare isotope, well then rare plus rare, rare times rare, is very rare. I'm never going to see these things. And so he gave up and he said you're never going to measure these things.

Wolf (10:19): And was it because he lacked the tools, the mass spectrometry that was required to do it?

Eiler (10:23): He just lacked the tools. The mass spectrometry was just not there. It didn't have the sensitivity. They didn't have mass resolution. And in ways that in retrospect feel trivial. He understood what he wanted to do, but he gave up before he could make an observation because he didn't have the technology. And because he couldn't make an observation, he didn't extrapolate the idea to fill out all of its implications, which ended up being, I would say, grandiose. So you start at this basic concept and then apply it to all of chemistry and apply it also to related questions. Like if I have a big complex molecule, not only could I ask what are the chances two rare tips are together? I might ask what is the chance one rare isotope chooses to be at one end or the other of that molecule? Or what if I had three rare isotopes? Would they wish to be separated from one another, all next to each other, two together and one apart, and so forth. When you think about it in this way, the problem blows up and many tools are implied by this that reach into biological sciences, medical sciences, and so forth. But you have to have the ability to observe to even start having those thoughts coherently and exploring them.

Wolf (11:41): Well you've developed something that's infinitely more complex. So, as I think about the layperson's understanding of stable isotopes, people who've followed climate change say, well, we look at tree rings and as a function of the stabilized steps in the tree rings, we can tell you what the temperature was back in time. Or we look at ice cores and we can say if there's this certain amount of deuterium in the ice cores, then we have an idea of what the paleotemperature was. You're postulating something that is infinitely more complex.

Eiler (12:10): Much more complex than this, and it's easy to grasp through a couple of analogies. So, the normal way of studying the distribution of these rare, stable isotopes in nature is simply to pick up a material. If I pick up this bottle of water and I ask: how many of the atoms of hydrogen in this bottle are the rare isotope deuterium? That's my question. And then I go off and devise a way to measure that and I return an answer. And off I go. And this is the quantification, counting atoms, irrespective of exactly where they are in the material. This is what people have been doing because this is what it was easy to do when Urey did this work in the thirties and forties. And it's what we basically continued doing. So if you do this, you immediately encounter a problem that measuring just the concentration of something in a material doesn't tell you that much about it. So for example, the simplest example that I think is a nice metaphor: My name is written with letters. Your name is written with letters. They're not written with exactly the same numbers of the same letters, but if you were to identify us, maybe I were to write a phone book and I organize my phone book by how many letter "Os" are in my name. One, John. How many are in yours? Wait, also one. We're the same person. No, we're not. There's other letters as well. And if you really want to know who we are, you have to know not just what letters are there, but what is their order, what is their geometric arrangement. And that's the information content, that's the richness of language, is the structure, the organization of these small numbers of things. And so the rare isotopes are just like this. If I see them in isolation, all I can ask is how many of this atom of, say, carbon or hydrogen or whatever, is the rare version? But if I see them in context, I see them in the structure of a molecule, now I have many questions that I can ask. Where of all the nonequivalent sites did it choose to be? Who are its neighbors? Are they rare isotopes or not? And the combinatorial versions of this explode, the combinatorial math explodes when you see structure.

Eiler (14:35): And I would say that the closest analogy that is more scientific and helps you understand not only what we're trying to study, but the potential implications, would be genetics. Get into your time machine. Go back to, say, 1970 and go to a biology department or an organic chemistry department and you say, tell me about DNA. The people there would say, I know all about DNA. It has a certain structure, it's a helix, has some carbon in it, some nitrogen, phosphorus, whatever. And then you could ask, great, now tell me about my DNA. Well, nobody can tell you about your DNA. Who could ever measure that in an individual and characterize the whole structure? Well, we can do it now. And because we can do it, we're able to read the richness of the structure, of the chemical structure, of the genome. And this is the same idea that motivates my work on isotopic structure. It's effectively a genetics of everything. Well, every chemical compound.

Wolf (15:41): Urey postulated that the positioning and the number of heavy isotopes was very important, and you took it to the next level in two ways. One was, you said, well, actually, whether or not two carbons sit next to each other in a longer chain is important. And the number of variables that you can look at is obviously very important. But you did something way beyond that, which was you actually measured it. You figured out how to measure.

Eiler (16:04): There's two other questions that you then have to address when you have this realization. First is how do I observe? If my goal is… every single object that I look at in this room is made of molecules and every one of them has rare isotopes in it. And all of them have an isotopic structure that is probably, in some sense, unique, that tells me a history of how it was made, but I can't see it. Okay, how do I get to see it? I have to attack that question head on. And then the second question is, before you take on this fantastically big observational project, what will it mean? Can you predict in advance what kinds of things could be recorded there? But you have to decide before you start doing your measurements, why am I doing it? Because otherwise you'll get lost. And so early on in this process I picked up another thread of Urey's thought and asked what are the tools that would emerge from the ability to observe isotopic structure in the same way that we can observe genetic structure. And one of them that emerges is a temperature dependence of this clumping phenomenon that gives its name to this branch of geochemistry. And the basic effect is pretty simple. If you have a material with rare isotopes distributed through its molecular structure and the temperature of that material is very high, then the randomness or entropy contribution to the energy of that system is very important. At high temperature, randomness counts more , and at low temperature, randomness counts less. And so at high temperature, randomness will win, energetically, and the rare isotopes will tend to migrate through the structure and be in randomly placed locations. And you'll notice nothing special about them if your reference frame is random as normal. Okay, now take that same molecule and bring it to low temperature. And as you go to lower and lower temperature, randomness becomes less and less important and you become more and more interested in the chemical energy content of the individual bonds that are present in that material. And when it gets cold enough, you will start to realize some of these bonds have a heavy mass on them and are vibrating slowly and are very stable. Those are good bonds, energetically. And the best bonds of all are the ones that are two heavy isotopes oscillating very slowly against each other. And so as temperature goes down and down and down, the materials will redistribute their isotopes, if they can do so energetically, they will redistribute their isotopes to stick them to each other. And this gives you, in the measurement of isotopic structure, a thermometer. It doesn't always work in all contexts, but when it works, it tells you the temperature at which that material was made independent of just about anything else that you might want to know about it.

Wolf: The exact temperature?

Eiler: The exact temperature. You could know the temperature at which your tooth enamel grew to within half a degree or a quarter of a degree.

Wolf (19:13): And in the evolution of the molecule? So, versus just locking it in an ice core, we now know something about the history of this ice core or the history of this molecule.

Eiler (19:22): That's right. Some molecules are very simple in their structures and it is only possible for them to record a single temperature, the formation of their bonds. Other molecules are much more complex, and they might have several different chemically distinct portions to them that are very different in their rates of re-equilibration, or their rates at which they find their low energy state at different temperatures. I might have one end of a molecule that is very refractory. It's difficult for it to change its isotopic structure and it might only tell me about the temperature at which that molecule first formed. And then another end of that molecule might have another chemical unit that's very labile and easily exchanges with its environment. And it is telling me about the last temperature it saw before I picked it up.

Wolf (20:13): This was mind blowing the first time I saw this. Once you figured out you could do this and you knew some of the pieces of information that you were going to get, now you have to do the hard work of going and applying it, and applying it using the scientific method to make sure you got this right. What were the first sets of experiments that you decided to do?

Eiler (20:31): I have taken a very purposeful view to this that I almost never show all the cards in the hand, but the hand has always been there, and I generally have been playing one card every five years in the way that this works. So, the end, the goal, the Royal flush that you want to lay down, is the ability to answer questions of formation condition, chemical mechanism, inheritance for any of the 50 million molecules known to science. That's the goal.

Wolf (21:05): Which would be an incredible achievement.

Eiler (21:07): An incredible achievement. But you're not going to get there in one step. First of all, you don't talk about that until you're close because everyone will think you're crazy. So start with something achievable and small and set goals that are very understandable. The first goals that were set were to determine the temperature of origin of the carbon dioxide molecule, or a chemically related mineral that we find in the geological record or in the human body or lots of other contexts—carbonate minerals, which also have carbon oxygen bonds in them. And I focused on it for several reasons, some of them technical. It's an easy molecule to study, the isotopes are abundant, there's lots of it, and it matters. You care where the carbon dioxide in the earth's atmosphere comes from because it does something important. It is a greenhouse gas. It acts in the chemistry, the acid-based chemistry, of the earth. It is a weathering agent. It matters. And the carbonate minerals are chemically related to carbon dioxide. In a way, they're a record of something that matters. And so they are widely distributed in the geological record. They tell you about the chemistry of carbonate in the past. They matter as well. And so the thought was we will take this concept of measuring the isotopic structures of molecules and we'll apply it to something where the audience, which is everyone, anyone interested in the sciences, they don't have to know what the long-term goal is. They don't have to know how it works. They don't have to know how it's being done. They will care about the answer. And we will get to the point where we're delivering impactful answers that matter because of the answer, not because of the way it was done. These are the things that we studied: a little bit of work on CO2 budget in the atmosphere, the carbon cycle that exists in the modern atmosphere, much more the study of the history of climate on the Earth's surface, and history of biology and its interaction with climate. So one of the funner things that we did was to study the body temperatures of dinosaurs and figure out are they responding to their environmental climatic temperature? Are they setting their own temperature like we do?

Wolf (23:26): So, were they cold-blooded or were they warm-blooded?

Eiler (23:27): They were both. They were sort of both. So dinosaurs, if you were to walk up to a big one, why would you bother with a little one? Right. The big ones are the fun ones. Walk up to a big one, carefully put your hand on it and it would feel as warm as a cow. So you might conclude they're warm-blooded just like me, but are they warm-blooded for the same reason? And to answer that, you need to see how does their body temperature change as they get bigger or smaller. And the biggest ones were at a temperature of like 41 or 42 degrees centigrade, which is, you're like almost bursting into flames biologically if you're that hot. They got almost to the point of dying from the heat. The smaller ones were actually at body temperatures like an alligator. So dinosaurs were, the ones you are thinking of, were warm-blooded like us, but not for the reason that we are warm-blooded. And so one of the questions that is not yet answered is was there a connection between their size, their body temperature, and where they live. We just know that they were doing something very different from what big mammals are doing.

Wolf (24:33): So, one of the things that's absolutely mind blowing is the number of different places that you can take this. Now, what?

Eiler (24:40): So my group goes through sort of five year molts you could say, periods where we take a concept, a scientific motivation, we connect to that scientific motivation a set of new technologies. Technology is never static. It's always moving forward. So we're always thinking, what is the next thing that needs to happen so we get to this dream of: observe everything in everything. And then we connect that to a specific motivation that is interesting, worthwhile, carries its own weight scientifically, but will be serviced by us reaching this next goal, technologically. And the current one that my group is really focused on is prebiotic chemistry. Figuring out what are the specific set of chemical reactions that interrelate the soup of compounds that nature had to create for life to emerge. And we're studying this in the laboratory. So there's a close collaboration between my group and people in chemistry—I even have graduate students who are chemistry graduate students work in my lab—and also to planetary science. So, basically, what you'd love to do is say, here is how the chemistry of life, the chemistry of organic matter on the earth worked before the emergence of life. And here's how it underwent a transition to the emergence of life.

Wolf (26:11): Let's go back to your students just for a second because one of the things that I know knowing some of your former grad students is how close you are still to them, how much they appreciate that relationship. You not only help spawn their careers, but you spawn their careers and you've continued to help them and collaborate with them. Could you say a little bit more about your philosophy around grooming students and your long-term relationship with them?

Eiler (26:34): I don't have a plan in mind for a graduate student who walks into my door, but I have a set of attitudes and I think they sort of stitch together into this good outcome that you're describing. One of them is: I just like working with colleagues who bring something interesting to the table and that can be a fresh idea, or energy, or an interest, or a background, or whatever. It can be almost anything. When they show up for work in the morning, you're glad they're there and you want to interact with them. So start with people who you want to be around and then they're going to feel that and want to be around you and want to be part of the group. So the group has a whole, pack together a dozen people who share all these values and they're going to get along very well together. The second thing is the students who enter my group, and the postdocs as well, who I consider part of the whole mix, no matter when you show up in my lab, you're showing up at a time when something is beginning. There are things that are mature and they're great, and there's things that are halfway through and they're great, and there's new things and those maybe are going to be great. And so anytime somebody shows up, they get to experience this whole arc of going from, "I can't believe you just said we're going to try to do that," to "We did it," and here's the papers and now off I go. And then the third thing is, I don't really want to stay focused on any one of these things. It's just the personal, you know, my personal drive. I'm very focused on the strategic goal of making the vision quest level of it, that I think about every day. The specific applications, I try to think about exactly the right period of time. Not too short, so nothing good happens. Not too long, so I get stale. Just the right period of time, three, four, five years, something like that. And then I move away and I start thinking about something else as a motivator. And that means we're spawning off little subareas that are all totally worthy of study, they're wonderful projects. You could spend a long time studying them. But I'm not studying them and so I don't show up and eat their lunch as they're trying to become assistant professors and build labs and things like that. I've gone and done something else.

Wolf (28:58): You still have a lot of ongoing collaborations with folks. I mean, it's like a special club of people that are in the clumped isotope geochemistry club. I'd like to join.

Eiler (29:06): Yeah. So, there are now dozens of labs that do this kind of work and there are different sub-disciplines involved. The biggest of them studies the carbonate minerals because they're such an important part of the geological record and they tell you such important things about Earth history. And so that's the collection of labs that is most interactive and that community is amazing. Yeah, there's a sense of trust, you will not get burned. We are all going to help each other make this thing better. Every time we interact, we're going to make it better. And so that community, it went through… all communities like this go through growing pains of figuring out problems, and this system works and this one doesn't, and this material is good and this one's bad, and this application worked and this one didn't, or I did it first or you did it first, or whatever. And so just getting the entire community to approach that with a really good sense of openness and mutual support, in a way, that's the thing I'm most proud of of the entire activity.

Wolf (30:13): And what's really incredible is Harold Urey had a lonely idea. It was so lonely, it was forgotten.

Eiler (30:19): Exactly. It was so lonely, it was almost forgotten. A critical moment where I noticed what he thought.

Wolf (30:27): Well, your fondness and interest in history, not only history in general, but the history of the field of geochemistry, plus an incredible idea around, truly a lonely idea around: this is how we can actually measure this and make this work has now resulted in not only an entire field but a group of people—I described it as a club, I like that—a group of people that are in a club who are making all sorts of incredible measurements and discoveries. If you have one final thought for all of those folks and all of our listeners, what's the one final thought?

Eiler (31:01): So, this experience came out of a moment in my own career that was a moment of transformation that was very intentional, but also a result of the circumstances that I was in. So I was near the end of my assistant professorship and I had just had a couple of good things happen for me, recognitions and things like this, that suggested to me, you're safe. You made it to second base, you're not out, the inning is still playing, you're still going. And my first thought was not relief. My first thought was, you know, I didn't really do it. I didn't do the big "it" of accomplishing something that really advances knowledge with a capital K. I hope it starts with K. And in the way that the people I most admired had done. And so the person who I most admired in—you know, there are a number of people who strongly influenced me, my PhD supervisor, John Valley; Ed Stolper, my postdoc supervisor—but the person who most spoke to me personally in terms of his values scientifically was Sam Epstein, who, was a founding person in stable isotope geochemistry and he had this very loose, open feeling of what is possible. Anything is possible to him and everything is interesting, and everything is possible. This was just the way he felt about everything that he encountered in the sciences. And, it led him to write paper after paper after paper that was a discovery, a mind opening approach to a new problem, a new field. He just stitched together different disciplines in the natural sciences naturally. And I knew: I have not done that. And it is my responsibility to try and do something like that. Maybe other people have other responsibilities to like figure out exactly, you know, the mass of the electron or whatever. Fine, that is your responsibility. My responsibility is to somehow follow his path. And so I really sat down consciously and did an inventory of what do I know and what do I not know and what is not known period by anybody. And what is the biggest thing out there that I know enough to attack that no one has solved. And it immediately occurred to me. This is basically, if the chemistry of isotopes is the study of all the different ways that isotopes can exist in chemistry, most of them had never been observed—like 99.99999999999% of all the richness of chemical structure of nature had never been observed. And so I said to myself, I'm going there, and I will just head in that direction and that can't be bad. I will succeed somehow.

Wolf (34:05): John, thank you so much for being on The Lonely Idea. This has been enlightening and a true pleasure and great to spend the time with you again.

Eiler (34:12): Great. Thanks very much for having me.

Conclusion (34:15): The Lonely Idea is produced at Caltech. Learn more about Caltech innovators and their research on our website at www dot Caltech dot edu or connect with Caltech on Facebook, Twitter, Instagram, and YouTube.