The Origins Podcast with Lawrence Krauss - Andy Knoll: The First Four Billion Years of Life on Earth

Episode Date: July 14, 2022

Andy Knoll is a Renaissance Scientist. He is a geologist, paleobiologist, and geochemist and has applied key ideas from chemistry, biology, physiology and more to understanding the key developments associated with life on Earth—both how geology and chemistry have impacted on life, and vice versa. He has made ground breaking contributions to the understanding of almost every phase of life, from early Pre-Cambrian single cell life, to the emergence of more complex lifeforms, to mass extinctions. His group was the first to demonstrate that the rapid rise of CO2 was probably responsible for the last great extinction on Earth, a subject of some relevance today. For his work he most recently won the Royal Swedish Academy of Sciences Crafoord Prize in Geosciences… the equivalent of the Nobel Prize in that field.But more than all of this, Andy is a wonderful teacher and human being, and a great communicator . He has written numerous books on the history of life on Earth, and we discussed his most recent book, “A Brief History of Earth: Four Billion Years in Eight Chapters” in this podcast, along with his own origins and evolution as a scientist. The discussion was so fascinating that we went overtime during our first session and had to continue the next day. Our discussion will forever change your perspective on our planet, and our place within it. Enjoy.As always, an ad-free video version of this podcast is also available to paid Critical Mass subscribers . Your subscriptions support the non-profit Origins Project Foundation, which produces the podcast. The audio version is available free on the Critical Mass site and on all podcast sites, and the video version will also be available on the Origins Project Youtube channel as well. Get full access to Critical Mass at lawrencekrauss.substack.com/subscribe

Hi, I'm Lawrence Kraus, and welcome to the Origins podcast. This has been an exciting week in science as the James Webb Space Telescope released its first images of the universe. One of those images was of a distant exoplanet surrounding a star, and it looked at the atmosphere. It was a spectrum of radiation coming from through that star, and you were able to see the absorption of water, which is clearly water vapor in the atmosphere. That's one of the main missions of JWST, which is to look at the atmospheres of extrasolar planets, to look at the for biomarkers and potentially evidence for life elsewhere in the universe. But of course, if we're going to understand life elsewhere in the universe, we should first try and understand life here on Earth and the evolution of life on Earth.

In particular, those things that may be relevant to the way life affected geology and vice versa. And in that regard, there's no better person in the world to discuss this topic with than Andy Knowell of Harvard University. Andy is a, it's hard to define him. He's a geopalientologist, a geobiologist, chemist, physiologist. He merges all those different fields to try and apply that expertise to novel ways of looking at the development of life and earth. And he has made major contributions to almost every single area from the pre-Cambrian life and single-cell life and the development of complex life on earth to in fact major extinctions. And his group was the first to be able to singeastern.

suggest that the sudden rise of carbon dioxide was perhaps responsible for the last major extinction on Earth. A very topical subject for looking at for today. Andy, for his work, Andy has been awarded basically every major prize in the world. He's a member of National Academy of Sciences as well as many other national academies. But two in particular stand out for me. One, he was given the International Prize in Biology in the presence of the Emperor and Empress of Japan. and Empress of Japan in 2018, and just this year was awarded the Crawford Prize of the Royal Suisse Academy of Sciences in Geosciences. That's essentially the Nobel Prize for work done in areas

for which there's no Nobel Prize, because his work has been so remarkable and innovative. And I have learned a tremendous amount from Andy over the years. I've actually, he tutored me early on on many aspects of development of life when I wrote my book, Adam, and we became friends then, I've enjoyed his writing ever since. He's written some very cogent books on the first few billion years of life and earth, and most recently another wonderful book, which we talk about in our podcast. And we also, of course, talk about not just the evolution of life, but the evolution of his own experience as a scientist.

He is a gentleman and a scholar and a wonderful person to listen to, and I'm sure you'll enjoy the discussion as much as I did. I hope you can wash the discussion on our substack site, Critical Mass, by subscribing to it because that supports the work of the Origins Project Foundation, which runs this podcast. You can also watch, of course, this video on our YouTube channel. In that case, I hope you'll at least subscribe to the channel to get more information on upcoming events and upcoming podcasts. And, of course, you can listen to the podcast anywhere podcasts can be listened to. Either way, I think you'll be as fascinated by the discussion I had with Andrew Noel as I was.

Well, Andy, thank you so very much for agreeing to do this. It's such a pleasure to be able to talk to you again after a while. I haven't seen you. So thanks for being on the program. And I'm sure it'll be enlightening. And I love the background behind you, which is not real. But my background is real. But I don't think you're doing this remotely.

But that background will be probably relevant to some of the things we're going to talk about, I think. Is, yeah. And I want to say in advance that you have been my teacher for many, many years. Many years ago, when I was writing my book on Adam and trying to learn something about the history of life on Earth, geology, and biochemistry, about which I knew almost nothing at the time, I must admit. I benefited tremendously from your wisdom and experience. And I'm really happy to do that again and to give other people an operational. opportunity to do that in the context of your newest book with a brief history of life on earth, which I want to use as kind of a guide to talking about some of the most amazing developments

of life on earth, which I kind of realized I never had put in perspective how important your research has been to a variety, almost all of those key markers that have been related to the early history of life and earth from the earliest history of life on earth, to the to the explosion around the Cambrian period and then to important things like extinction. And I guess I guess I realize how important it is because I wasn't the first person to realize how important it was. Most recently, I want to congratulate you on the Crawford Prize, which you were just awarded a little while ago, which for if people don't know, is essentially the Nobel Prize in

fields for which the Nobel Prize isn't given. And I was just so pleased to see that you were awarded the Crawford Prize in January of this year, which I guess you'll accept in April. What an amazing honor, well deserved, as we'll see. So congratulations on that. Well, thank you, Lawrence. I appreciate it. It's a wonderful thing to think about the one of the things that is, and I want to, this is the origins podcast.

So we're going to talk about the work you've done. But first, I want to talk about your origins, which I know a little bit about. but of course I want to learn more about. One thing I don't know, I know you and I have talked about the evolution of your time a little bit from your PhD at Harvard to Oberlin back to Harvard. And I do want to go into that a little bit, but I want to go further back. What got you interested in geology and science originally? Well, to be honest, you know, when I was 18 years old, I hadn't the slightest idea

what I really wanted to do in life, which probably doesn't differentiate me from most 18. No, but well, it's, that's a, I'd like to say that's a great thing. I'd be sad if, if you're 18, you knew what you wanted to do. I mean, for some people, I agree. Yeah, yeah, yeah. Yeah, and so I, you know, I grew up in a rural part of the Pennsylvania Dutch country. And to be honest, you know, I'd never met a PhD. I, uh, as far as I knew there were maybe three professions, you could be a doctor, a lawyer, or an engineer. And I knew I didn't want to, to be a doctor or a lawyer. So I went to engineering school and then being really a bright teenager, I realized after a year that I didn't want to be an engineer either.

Important realization. Yeah, the first semester of my sophomore year, almost out of desperation, I took just a whole load of science and math courses, just hoping something might, you know, really strike me. And the miracle was that two things did. One was I took a course in biology and fell in love with it. And the other was I took a course in Earth science and decided that the history of our planet was interesting. And then in probably the only real insight I think I've ever had, I was sitting in my dorm room and it dawned on me that maybe Earth and life sciences weren't the separate universes that they seemed to be from the courses I had that maybe in a lot of ways they were two sides of the same coin. And that, you know, once I, had that thought, you know, everything proceeded from that. Well, you know, that's an amazing realization. And I will say, and you can correct me if I'm wrong, that those two disparate disciplines became one largely because of your work,

as far as I can tell. Well, that probably gives me too much credit, to be honest. But I did come along at a time when people who were thinking about an integrated view of earth and life. were no longer these voices in the wilderness, that I think the world was becoming more receptive to it, both because it gave us a better sense of the history of Earth and life, and importantly, because you have to have this perspective

to think about the future of our environment. You know, it's amazing if you can be at the right time. A lot of progress in science is hard work, but some of it is luck, and being at the right place at the right time, helps. And it's interesting that you say that that was beginning. The tools were just beginning to be there and the people were beginning to be interested. And, you know, at the wrong time, it can be a waste. I think I've said before in this program, I remember when I was doing my PhD at MIT down the road from where you were at Harvard, but a little bit later, I got discouraged in particle physics and I thought of going into bio physics. And I was going to do a joint PhD MD at Harvard.

MIT and then someone, the uncle of a friend of mine who was a head of cellular biology at Harvard, said, don't do it. Don't do it. This was in the late 70s. And he said, because biophysics isn't of interest to biologists and it isn't of interest to physicists. And he may have been right at the time, but of course, 20 years later. A decade later.

Yeah, exactly. A decade later, it was exactly wrong. But you were there at the right time. But I want to even go back further. Before we talk about the biology, it's interesting to me that you say you'd never heard of PhD either. I mean, I wonder about, I have a friend of mine who became a physicist, and he wrote a poem, I think, in kindergarten. When I grow up, I want to be a doctor of philosophy. And I was amazed, because I would never have known, he's now a professor in British Columbia.

And he did a PhD at Harvard. But I never, I thought that notion to me, it was doctor or lawyer, because neither of my parents had ever really finished high school. And so I'm wondering about your parents, what, what their background was. Well, you know, my parents grew up during the Depression,

which had, you know, understandably and important influence on their lives. And my dad basically went from a depression era high school into World War II. So he didn't have time to go to college. And when he got out, you know, he wanted to settle down and became a bank teller and blah, blah, blah. My mother, whose father came from Germany and was more, I think education was more central in his view of the world. He was an engineer. She did go to college and became a teacher. So my parents, you know, they were, good hardworking people they they always supported me i think when i told them that i was going to become a uh geologist and billionologists they secretly worried uh you know my mother i think she actually told me that she stopped worrying about my career when i got tenure at harvard okay

maybe he'll be okay good okay that's you know that's good that's good that she didn't continue worrying after that i think my mother continued worrying after that still but uh um that's okay but she was the so She was the one who'd gone to college in terms of encouraging. Now, you said a doctor, lawyer, an engineer, and you chose engineer, did either, in terms of science versus, say, history, or anything, other academic stuff, did she, what, she went to college and studied what?

Basically education, home economics, and then she became a teacher after that. Okay, did you read, I mean, what got, what made you decide to do engineering? Did you read science as a kid or did, What did or was it anything? Some. The one book I really remember that an older neighbor gave me when I was about 10 was a book called All About Archaeology by Terry Ann White.

And to me, it was exciting. And you know, you can actually draw some lines between my excitement about that and what I ended up doing. Because it just told these stories about how if you knew where to look for it, there was history underneath your your feet and i just thought that was the greatest thing i was probably the only 10 year old in my town whose hero was heinrich schlemann but yeah no i i must admit that when i was a teenager i was i liked writing and that's something that i've continued to try to do um i was probably more interested in music than i was in in in science and and i'd have to be honest on a I rarely got up in the morning and thought, hmm, what should I do for my life?

I was more worried about, you know, what I was going to do on Saturday night. That's such a nice thing. I wish more kids had that experience now. Too many kids nowadays, as you know, and I mean, and, you know, being at Harvard and living in sort of an academic community, I've always been amazed when I taught New Haven. The people, parents are worried with their kids, how well they're writing in kindergarten or whatever it is. I mean, they're worried about what college are going to get into. And it's, it's kind of sad that kids are so programmed or pre-programmed now instead of that time to just

spend time thinking about the world and deciding where they fit in within it. Yeah. Yeah. And, and, but that's good. Okay. So you, and it's interesting, it's nice that you were able to integrate that writing thing. Did you follow up on music, by the way? Did you, what, Well, music has always been important avocationally. I actually met my wife. It turns out, like many people of my generation, I went to a college that was all men at the time. Yeah. And she was at a woman's school. And so we got together to sing choral music. You know, in both in graduate school, we both sang in the chorus pro music, a very, very good chorus in Austin. When I taught at Oberlin for five years, we were.

were in the Oberlin community chamber singers. And so music has always been important and I wouldn't want to have a life without music. I think somewhere along the line, I realized that, you know, I might be a good high school teacher of music and which I have the greatest respect on earth for people who do that and succeed in it. But I think I realized somewhere along the line that I didn't have the talent to be the next Pavarotti. Whereas, you know, at least maybe I had talent to do some good things in science. You know, you just reminded me of a story. It's interesting, a story that I learned many years ago from Donald Glazer, who was, who was won the Nobel Prize in physics, and he was at Berkeley. And he was, and he was interested in music. He played the violin, I think,

and he was also sort of interested in science. My dog and cat are fighting here. I'm going to have to just wait one second. I'll be right back on and remove them. Anyway, there we go. I knew they were going to at some point decide they didn't want to hang around here. Okay, but anyway, let me repeat this.

So Donald Glazer won the Nobel Prize in Physics for discovering a new way to detect elementary particles, actually. But he told me a story. He was a violinist, a pretty good one in Cleveland, which has a great oral. orchestra and I know Oberlin's music because it's you know I lived in Cleveland for time and my daughter played the violin but he told me um uh his father told him you know you're an okay you're an okay uh violinist and maybe an okay scientist uh but as a mediocre violinist you'll

never get a job but as a mediocre scientist maybe you will and I thought that was so he's he went into science because he figured even more have chance of that he's right now one of my strongest memories from Oberlin was going to concerts at the conservatory and you know hearing young musicians who were to my way of thinking astonishing and knowing that probably every one of them wanted to be on the stage at La Scala and most of them would never make it so you do have to be exceptionally talented you have to be exceptional that kind of career in music yeah it's amazing because of my daughter who was very musical I got involved you know got to see that firsthand in Cleveland with the Cleveland Orchestra and it was really kind of amazing to see and going to Aspen where

there's a physics institute but also a music school to see the the rungs and how many great young violinists there were and they were going to be they were going to remember their time as great young violinists but they were going to be employed so that yeah you know it's lucky you chose that then and and ended up okay as a scientist but okay so you you as an undergraduate and and and you were let's see you do a PhD at Harvard you do your undergraduate degree where again I forget at Lehigh University in Pennsylvania in Pennsylvania where you'd grown up in Pennsylvania okay but I and I remember talking to you about this when we first met you you chose to go after your

PhD at Harvard to Oberlin which is an unusual thing for anyone to do I in fact it's interesting to me I actually had a student who did his PhD at Harvard when I was at Harvard as a junior fellow and he worked with me. And then he went to do his PhD at Oberlin, I think I, I mean, to win in to teach at Oberlin right after that. And interestingly, at the time I thought, okay, well, that chooses a career trajectory, which is not research, it's teaching. And interestingly to me, later, years later, he contacted me for a letter of recommendation. And I wrote it and I didn't know what he was, what experiment he was going to be working on.

And it turned out to be the Kobe causing background satellite. And he became, and now he's a professor. You know, that was a huge experiment. And he moved back from Oberlin to become a researcher at NASA and then moved to become a professor. But why did you choose to go to Oberlin instead of, say, a more traditional trajectory as a PhD, as a postdoc somewhere doing research? Well, a couple reasons. First of all, when I finished my PhD in, which was in 1977, it was not the standard practice in Earth Sciences to do a postdoc. Oh, I didn't know that. It is now, but some people did it, but many people went right into a profession. And to be honest, at the time, I thought a place like Oberlin was just ideal. A, there's all the music.

And B, you know, I saw a lot of things that I didn't particularly like about the research environment at Harvard in the 70s. And so, you know, I wasn't fleeing from it, but I realized I didn't have to do that. And I might be happier if I didn't. And then to be honest, in the course of time, first of all, I should say, I'm always grateful that I had five years in Oberlin because not only did I learn to, teach, but because there was no pressure on me to get funding yesterday and that I didn't have to keep on doing what I had been doing. And I had the luxury of as I learned to teach, to think about what was really important to me. And that really changed in my research trajectory. And then it turned out, you know, fortunately, I had good luck in research and realized that there were at

Oberlin or any other liberal arts college, although they support research, there are walls to what you can do. And then Harvard came around and said, well, you know, we have an opening. Why don't you apply for it? Since it was actually in the town where my wife had an elderly father, yeah. And, again, it worked out. It worked out well. But I mean, you know, the point, I think it's nice of me to say that, but Harvard doesn't just come around tapping on your shoulder if you haven't. It was very fortunate that while it's interesting to me, as far as I can tell from your history, that while you were at Oberlin, you did your first set of ground-breaking research, if I'm not incorrect. Is that true? Yeah. Things worked out well. I started doing field work in Spitzbergen,

which turned out to be this wonderful geologic library for a portion of Earth history. I started in collaboration with the Lake John Hayes to do geochemical work on those samples. So, yeah, the world of research really did open up on that time frame. And I could do it from Oberlin, at least a certain amount of it, because the paleontological part didn't require special equipment, the geochemistry I was doing in collaboration. So I could make it work. Okay.

I was wondering about how you balance that. I was also wondering whether the opportunity at Oberlin, you know, teaching during the year, whether the summers became a key point for able to do field work or a, and where, and if you did that, where the funding came from. Yeah, I mean, one of the great things is that the National Science Foundation on that time scale recognized that, you know, a disproportionate amount of their funding went to the East Coast and the West Coast. Oh, I see. So they were very interested in finding things that they could fund somewhere in the heartland.

And so I benefited from that. So I did have NSF funding while I was at Oberlin and actually started working with NASA on that timescale as well. So to do a certain amount of meaningful research, I had the support of, of people at Oberlin, I had had some funding. But I do remember talking to one older professor who at some point in his life had to make this decision between a predominantly teaching career and research. And he made teaching and was miserable for the rest of his life.

And I should say that I know a lot more people at Oberlin who just thought they were the most lucky people on earth. And the college is lucky to have people like that. Absolutely. But I realized that I just couldn't, you know, at that point in my life, say the most central thing to my professional life will be this institution. And, you know, I figured, you know, Harvard was not, let's be honest, famous for tenuring junior professors at the time.

But I realized that if Harvard spit me out at the end of my term, It would have been an important time for my family because of my father-in-law. And I could at least at that point and said, well, I tried it. Yeah. And it's not a bad place to jump off from if you have to. Oh, yeah. Yeah. And yeah, no, and your point about, it's interesting, your point about the liberal arts college,

you're absolutely right. I mean, I, in various times of my career, had these positions where I visited liberal arts colleges and gave lectures, Sigmic, Cy, and Fabi. to capa kind of thing. And it's amazing to see the people who are, you know, if you're right to, there are faculty who are so dedicated and involved in teaching and thrilled. And the small liberal arts environment is such a different environment getting, you know, the students and the community. It's all, but I like to think of it as in some sense the same match of students. You know, my daughter, my stepdaughter didn't go to liberal arts college because they were

kind of, they were more urban and needed to be in an urban community. So, when I tell students when you're thinking about where the best place to study is, it's not, you'll get a good education anywhere if you spend time and effort and work on it. You might want to tune it to where your predilections are, whether you want to, you know, and I think the same is true as an academic. It works best if you can tune yourself, if you're fortunate enough to be able to find yourself in the right place. And it's not all, and as an academic, unfortunately, you're not always able to make that choice. It's more as my, yeah, it's more like the army sometimes where you told where to go. Okay, but the last thing I want to talk about in terms

of your background before we move to the science that I want to go. Well, actually, this is the science, is this statement that you fell in love with biology, because what interested me is you went from Oberlin as a, you know, you were in the geology department, I assume. Yeah. And you were offered at Harvard to be a professor of biology, if I'm not incorrect. Yeah, that's correct. But it, In some ways, that is kind of the way you make your bins. It turns out that I was hired to succeed my mentor, the late Elso Bardhorn, who was hired in the 1950s as a paleobotanist.

And so that's what they were looking for. And that was in the biology department. And in many ways, I'm glad that that happened because a, you know, for most of the, the last 40 years, I've been a member of two departments. Yeah. But in really having close colleagues who, when I had a question, I could just walk down the hall and talk to someone who has spent the last two decades thinking about this biological problem, that I think brought much more richness to my research on the earth.

Oh, yeah, absolutely. And let me ask you a question. And I was going to, so you took a biology course, but you didn't. In graduate school, did you take graduate course in biology or not? Yeah, I think both as an undergraduate and a graduate student, I probably had about the same number of courses in biology and earth sciences. I think the other important influence on me as an undergraduate came further along in my undergraduate life. But I just took a course, it was called something like an evolutionary survey of the plant kingdom. And it was, know, basically phylogeny and just the diversity of photosynthetic life. And we had to do a term paper.

And I ended up doing it on an idea that was new, exciting, and controversial at the time, which was Lynn Margolis's hypothesis that the chloroplast originated as a free-living cyanobacterium or photosynthetic bacteria. Yeah, we'll get to that. That was captured and reduced to metabolic slavery. And I just thought that was the best idea I ever heard. I still do, by the way. Yeah.

And when I was doing research on Lynn's early work, I would keep running into reports of this guy at Harvard who was discovering that there was, you know, a record of life, microbial life, that long preceded the origin of animals. And so it was really thanks to Lynn that I discovered this world of early life, early earth. and that's then what I went to do in graduate school. Okay. Okay. And Lynn, yeah, was important.

As a pot of soul to that, my first year in graduate school, I was sitting at my desk, and Barghorn comes in with this relatively young woman and says, Andy, I think you should meet Lynn Margulis. And to me, it was kind of like saying, here's Joe DiMaggio. Yeah, wow. Yeah. That was wonderful. And she was a friend for 40 years.

Oh, really? That's great. And she was a great scientist and happened also. have been the wife of Carl Sagan and who was a who had a good career in popularizing science and and yeah no that is an amazing story actually but let me ask you a question then because in this regard I didn't realize you had done so much biology in in graduate school and I tell students that I mean the whole point of being it can make it or anyone is lifelong learning is that is learning after school and so I

it turned out I became a professor of astronomy as well as physics my whole career. I never took a course in astronomy my life. And even in the kind of physics I do, I've told kids that I learned a lot more, certainly a lot more astronomy and certainly a lot more physics after I got my PhD than before. I'm wondering in the case of biology whether that was the same thing for you, or... Yeah, I think you put your finger on a very important point, and that is maybe the best thing you can learn in school is how to learn. Yeah. Because, you know, if you're at all curious, you're not going to keep doing the same work for your whole life. And that means you're going to have to go into fields that you don't know much about and learn. And if you can do that, you can

have, you know, every day is exciting. Yeah. And it's true. And it's, it's, and I mean, that and the whole point is I hope. And one of the reasons I do part of what I do. And I think you, the same is that everyone should have that opportunity and experience. And one of the nice things about writing books to the public is to give people that opportunity. And so one hopes that for everyone life should be a lifelong learning experience. And that's actually, I think for me, one of the reasons I'm interested in promoting science is not, I mean, obviously the subject matter is of profound interest to me. But the scientific process of how to learn and how to get information is to me the most important thing, legacy of science for society. And as we face, and we'll get later on in this discussion,

the challenges we face as humans, without that scientific process to face those empirical problems, we're going to be in trouble. You know, I wrote a book about 20 years ago to try and explain how we knew about the early history of Earth, Earth and life. And I had been frustrated in that so much of both teaching and public explanations of science was what I call the received wisdom. Yeah. You know, it's almost, you talk about the history of life, almost like it was the generations of Abraham.

Yeah. And there's no, no sense of how do we know that? So in that book, I took special pains to sort of try to take the reader out into the field with me, you know, what you encounter these rocks? What do you look for? What do you do with them? How do you use insights from living organisms to try and make sense of them? those. And I think, you know, in all teaching this question of how do we know what we think we know

is really important because it, you know, it's the one counter you have to the person who says, I don't believe there's climate change or I don't believe this. And, you know, if you actually know, well, here's what we know. Here's how we know it. Now give me your story in equal detail. Exactly. And, you know, because it's it, you, the appeal to authority is just, it's not. It's not learning. It's really, and it's, and it's, and it, uh, that, the, the process of how we learn what we know, I think it's incredible. By the way, you know I used your book in my, in my, I used in classes that I taught, um, a lot because I, I like to teach physics for non-scientists, but I like to talk about the earth in the, in the general context. And so there, that book of

yours was useful. And I remember we were talking about it when you're writing it. In fact, um, the, uh, and and, and I, and I have. exactly the same viewpoint. I think the whole point is, especially when it comes to fundamental physics, which seems so weird, rather than accepting it as sort of on faith as if it's some weird other story, the question is, why do we believe and how do we believe, how do we know enough to say these crazy things actually happen? And as opposed to sort of geology, although some of the things that we'll talk about are very non-intuitive also and need to be understood for, we'll jump ahead, but I mean, we don't, we'll talk about it more, but I remember I think it was probably

from you that I learned the remarkable fact, which is so central to his understanding of life on earth, that the early earth didn't have oxygen in the atmosphere, which is incredibly important. And I was totally unaware of it. And that fact is so non-intuitive when you think of oxygen as such an essential part of everything on earth now. And the fact that ultimately it was life that produced it is profoundly important. But let's start, speaking of oxygen, let's start. So I want to go through questions or discussions and it'll give you the opportunity to explain things. And I think I'll do it for the most part along the lines of your new book about the stories that are in the new book, the brief history of life on earth, which presents this beautiful

sort of understanding of the interplay between biology and geology and and the and it's and the other thing I guess which is really kind of neat about it that I hadn't appreciated so much before so i learned something every time i read your stuff um is uh not just that it's a i knew about the interplay of biology and the earth but the interesting interplay of the earth on biology is very important at various stages in the earth that we'll talk about so let's but we the first sort of chapter is called chemical earth and so i mentioned oxygen but we're going to talk about that later But the fact that the Earth evolved in a solar system around the sun in an emerging environment is of incredible importance. And the ability to use our understanding of the early elements that form the earth and where they come from is also an emerging field.

that it's changed a lot in the last 50 or 60 years. Obviously, I can't go through all of that in detail with you, but there's a few things I wanted to talk about. One is, of course, the importance of meteorites of understanding the materials that came to Earth. Why don't you talk about the early formation of the Earth in terms of meteorites? Yeah, it turns out one of the things I've always told my students is that we live on a planet that records its own history in the form of rocks that are laid down through time.

But the second part of that thought is that while the Earth is writing its history with one hand, it's erasing it with the other. So as you go back through time, you have less and less of a record still preserved. And in fact, we literally have no rocks that originated on Earth that are older than 4 billion years old, although there is pretty much consensus that the Earth originated more than 4.5 billion years ago. So it's really sort of Earth's dark ages,

and a question is, how can we know anything about this earliest history of our planet? And a big part of the answer is that we have access to the material, that accreted to form our planet in the form of certain types of meteorites. So since they do us the favor of sometimes landing on Earth so that we can study them, we have this beautiful, beautiful entry into our solar system as it was forming. And I think it's worth saying that everything that happened to the Earth in the ensuing,

four and a half billion years after it formed was potentiated by the chemistry of those starting materials if they didn't have water we wouldn't have water you know if they didn't have nitrogen we wouldn't have a nitrogen rich atmosphere so it's it's very informative to study meteorites and as you say we just every year we learn a lot yeah we're still learning a lot i remember when i first so you know these meteorites that the the old meteorites are really recorded the earliest history of the socialism. And by the way, you said consensus, but I worry about people thinking that sort of scientists vote on things. There's really good, you know, especially when we get to climate change. It's, we know that the age of the earth to actually end the age of the

social system, really high accuracy, 4.54 billion years. It's not as if it's, I mean, there's many independent ways of knowing it. So I don't want people to get the impression that it's just some something that we vote on or anything. But these oldest meteorites that come, carbonaceous chondrites, I guess, that come from out of part of the solar system. Yeah, there's new things. We're learning about the elements in there, but I remember the first time I learned that there are amino acids in these things. I remember, wow, that was, I don't know when that was first discovered, but I remember learning about it. It was really a bit. 60s maybe. Yeah. It was, and that alone, hey, that's highly suggestive of something important.

be very important as we try and understand the history of life and earth, not just that the raw elements, the carbon, nitrogen, and phosphorus and other things came from these meteorites which are building up the earth, but also that maybe even primary organic molecules that were very important for perhaps jump starting life on earth already preexisted, that the chemistry, it was amazing for me to think that chemistry in space could somehow produce things like amino acids Yeah, I think what I take from that observation, which is really cool, I agree with you, is it's possible that some of those materials may have actually survived in their trip to the earth as amino acids and played some role in biogenesis. But I think unequivocally, it tells us that the kind of chemistry that we think led to the origin of life is not some abstruse. rare chemistry. It's the chemistry of the universe. Yeah, exactly. And we'll get to that when we talk

about the chemistry of life a little bit because, you know, there are many questions about the original life. And I've just been writing it actually about it in the new book I'm finishing. But, you know, it's not only how, but where. And it's an interesting question when I want to talk to you about in a bit. So meteorites help form the Earth, but they give us this information about the Earth. And we'll get to water because, again, something has changed a lot from the time you and I first talked when you taught me about the water problem, which that book was written around 2000, and there was a big problem of where the water and earth came from that still hadn't been resolved, but now I understand it seems to be understood. So we'll get to that, but hold, which I was reading in the new book.

The, the, um, not only was that material important for understanding then how the earth formed, but the way the earth formed is something that's also important, that there are layers in the earth. earth that we're first kind of realized. And what do you, and as you say in the book, you might have thought, well, that meant the earth was sequentially built up. But we now understand those layers come from different physical processes. So walk us through that a little bit. Yeah. You're right. If you cut the earth in half, I've sort of used the analogy to a hard-boiled egg, that there is this central part called the core, which is largely made of iron. It's surrounding. by a thick second layer called the mantle, which has a variety of rocks rich in silica, iron,

magnesium, and that. And then just the outer veneer is the crust, the world that's familiar to us. And it's now pretty clear that as Earth formed, it may not have been entirely homogeneous, but it wasn't layered like this. But what happens is when, you aggregate all of these things together by gravity, you get heat produced. There must have been a much higher concentration of radioactive materials at that time. They produce heat and the earth melted. And the heavy stuff, the iron went down into the center. The mantle formed around it. And then through time, parts of the mantle differentiated to give us this scum on the surface we call call continents. So it really is, it's a planetary process. And once again, because of the outcome of

that, the physics of the core gives us a magnetic field, which is important. Yeah, I was going to ask you about magnetism, but yeah. The, the property of the mantle allow it to convect, which actually really is the motive force that determines, you know, what you see when you look around, mountains and valleys and ocean basins and that. So again, we had the right combination of materials and the right history of heating and differentiation to result in a planet that was and has remained very active in its. interior. You can, you can, you know, compare that to Mars, for example, which, you know, was probably active very early on, but most of that activity ended a very long time ago. It cooled, it cooled faster than the Earth for a variety of reasons, I guess. And I want to get to Mars at the end, too, because the differences between Mars and Earth are incredibly important. One often learns about how things happen in one place by seeing how different it is in another place, I mean.

The, you know, I was thinking about this in when I was thinking about the early Earth and the molten aspects. I didn't, I don't see this as an argument. Maybe you can use it. But I think if people are suspicious, maybe it wouldn't work because it still requires some belief in science. But are suspicious of the fact that the earth was molten. In my early research, actually when I still at Harvard, and I didn't know much about anything, I was learning about geophysics in the context of a particle that I like, one of my favorite particles in nature called neutrinos.

And I discovered that, hey, the earth is a rich source of anti-neutrinos, it turns out. And I proposed at the time that if you measured these things, you could learn about the interior of the earth. Of course, it meant to have to learn about what the ideas were. But one of the things that I didn't have any idea of the time to lead to my research was that most of the radioactivity of the earth is in the surface. because if it wasn't actually, you could show the heat produced, if there's as much radioactivity in the rest of the earth as they're in the surface, the earth would be much hotter than it is,

and the heat outflow from the earth would be much greater. And it shocked me, and I thought, why are these heavy things like, you know, heavy things like uranium and other things on the surface because they're heavy? And shouldn't they fall towards the center like iron? And then I asked someone who knew chemistry, and enough chemistry to say, no, they're in the molten thing, they're big ions. They're very large ions and they float in a molten environment. So in some sense, the fact that the radio activity is concentrated on the surface of the earth is kind of proof that it was molten.

Is that a good way of thinking? Yeah, no, it's reasonable. It turns out that a lot of these big ions, as you pointed out, things like uranium and that don't fit well into many crystals as they form. So since different minerals actually melt and crystallize at different temperatures, what happens is you start with a material called basalt, you know, essentially what you'd find if you went to the Hawaiian Islands, the volcanic rocks. And as you heat that up, some parts of it start to melt more than others. And the materials that, you know, it's kind of like the loners in high school, they don't mix into minerals very. well and so they get caught up in these things that rise up and form the crust and so you're right there is a concentration of a variety of of elements including many radioactive isotopes

in the in the surface now that said uh i think we all agree that the earth's interior was hotter yeah early on that it is now it's been basically getting rid of heat ever since and that has real consequences for the overall history of the earth you know that's an interesting fact because when in 1980 i think i wrote that paper in 84 there was still in i when i looked up there was still some debate about whether the earth was heating up or cooling there's still some people who thought the earth might not be cooling at the time so i don't know if that's changed a lot in the intervening no i think we've all they were outliers and the people who claimed to me that okay they were outliers yeah no no the earth has cooled through time yeah and by the way that

process of sort of pushing those materials that are loaners out is used in but if you were an engineer now in industry i think something called zone refining where you heat up materials and and and by doing like silicon and and you you get rid of the impurities by by refining it that way so the um the so but let but now i want to so that we talked about that but one of the key things one of the key materials that is important to understand how that crust formed when we talk about the how how we know these things we've now talked about what happened is zircon and and and it's incredibly important for understanding for dating that early formation of the crust and understanding processes related to the chemistry of oxygen in the early earth as well and and I want to

I want to know if you could take me through that and I and also take me through your own research in that regard. Okay, well, it turns out that while what I said earlier that there are no terrestrial rocks older than four billion years, there are some terrestrial mineral particles older than four billion years. And you might say, well, how can that be? And I would simply say, you know, if I go to the coast of Massachusetts and dig up a bucket of sand, it turns out the sand grains that are along the coast now were basically eroded from the white mountains in some granitic rocks. They're about 400 million years old. And if you poke around in those sand grains that are accumulating around the coast today, you will find zircons from those mountains. And zircons are the geologist friend because they contain a small amount of uranium. And some of that is radioactive. And we know from laboratory observations and

experiments the rate at which uranium breaks down to lead. And so they're chronometers. They're clocks. But there's one step here that that I learned from you that we should make clear you might say, how do you know the lead wasn't in there originally? So maybe you can also explain it. Right. Yeah, that's the beauty. I'm glad you bought it up because the great thing about zircons is that when the crystals form, the lattice or the three-dimensional network of atoms that forms the crystal will admit uranium into the lattice, but it does not admit lead.

And so any lead that you find in a zircon later on has to have originated. by the breakdown of uranium. And these things, I used to liken them to the flight recorders in airplanes. You know, something catastrophic can happen to the airplane and the flight recorders are still intact. And zircons are very much like that. Why is that, by the way, I don't, why are zirkins so stable? I think they have a very high melting point.

They're not easily changed by pressure either. So, and it's not easy to have actually exchange materials, you know, in the solid state between them and their surroundings. And so the result is that since we know from modern processes and younger geologic times, the kinds of physical circumstances that give rise to zircons, we can actually use those to look back. into that dark age. And there are zircons that go back to that 4.4 billion years. 4.4 billion years. That's amazing, yeah. Within 100 million years of the earth forming, which is amazing.

And we learned some things from that in a number of ways, and we'll get to some of the more, maybe controversial things about that. But you all say the chemistry that tells us about the chemistry of both of oxygen, which we'll talk about a little more later, but also the presence of liquid water at early times, which is surprising. And that'll lead us to water. So can you tell me how,

from looking at zircons, you know about the presence of water and maybe oxygen chemistry? Yeah, it turns out that the mineralogy or the chemical structure of zircon is zirconium, silicon, and four oxygens. And so oxygen is part of that mineral lattice. Oxygen comes in three distinct flavors. Their most oxygen is oxygen 16 with eight protons, eight neutrons, but a small amount is oxygen 17 with one extra neutron. A small amount is oxygen 18 with two extra neutrons. And using an instrument called a mass spectrometer, you can actually analyze materials and see the ratio of these ions. And it turns out, that that provides a signature because in the presence of water, liquid water, that ratio will be

different than it is under other circumstances. So using that, people were able to show that at the time these zircons formed, there was liquid water at the surface. Which is amazing when you think that's within a few hundred million years of the, of the, of, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the, of the. of the. of the. Of the. And of the. And of the. the earth that there's liquid water and oceans potentially and that that itself is surprising and the and it's surprising when you when you you you point out that the that meteorites and and and are not only help build up the earth their early chronometers but they but it's surprising when you think of where the earth formed why there are any of these what you might call what we call volatile materials we think certainly that what temperature when the earth formed with something like a thousand degrees in that

region, I think is a rough temperature in the early solar system. You don't have water around or, you know, and and yet we have a water covered planet to first approximation. And the question, of course, that arose early on and has probably very early on and was a center of sort of development in this area is where did the water come from? And so maybe you want to walk us through that. Yeah, it turns out that we tend to think of water as this liquid or an ice, but there are a lot of minerals that actually have water in their crystal lattice. A good example is gypsum. Everybody's seeing plaster of Paris and things like this, and that's a calcium sulfate, but its whole formula is calcium sulfate. 2H2O.

And so I think that much of the water that was incorporated into the meteorites that then were incorporated into the earth was in the form of what geologists usually call water of hydration, you know, it was not free flowing water. And then as the earth decreed and started to heat up, these and other volatiles were sort of released and degassed up to the surface. And in the atmosphere, of course, in the early atmosphere. Yeah, that's right. The liquid and gaseous surface of the earth both came from that degassing. In fact, it's kind of interesting that there's a lot of mounting evidence now

that because the earth's interior was hotter in the past than it is now, turns out the amount of water you can actually stick in the mantle varies with temperature. And so it's thought that maybe actually a lot more water actually degassed to the surface, you know, more than four billion years ago than is at the surface now because today there's, you know, at least one and perhaps several oceans worth of water in Earth's mantle. And increasingly people think that's water that was once at the surface and has been carried back down again by plate tectonic processes. And that's kind of interesting because if that's true, then, you know, if you had flown in an airplane around the earth four billion years ago, it would have been largely a

water planet with some volcanic arc sticking up, but not these extensive continents that we see today. Yeah, that was fascinating me when I read that and actually in the new book, that the, that the more, it's a two-way process that water goes out, but it also goes in and it might have and it might have been more water going in than out since that time. That was, that's the first time I learned that. But one of the things I did learn, I think from you a long time ago, anyway, as I was is is that while it makes sense that water came from from in this form from minerals that were embedded in in in meteorites nevertheless if you the water the planet is bombarded by comets which are snowballs and it and and calculations show that there

has certainly been enough material but enough comets bombarded the earth since its formation that you might have populated the oceans with those comets, but we know they didn't. And we know they didn't because of looking of isotopes. And that was the mystery that was around in 2001 when I was sort of first learning about this. So maybe you could walk us through that a little bit. Yeah, you're right. You know, a major reservoir of volatiles in the solar system is comets. Fred Whipple called them dirty snowballs. Yeah. That was a great name.

And so they are viable candidates for being contributors to the composition of the earth. But as you noted, they have oxygen and we can compare its isotopic content to what we know about the earth. They have hydrogen. We can compare its isotopic composition. And the view is that, you know, knowing that, you know, knowing that. and knowing how different it is from the isotopic structure of those elements on Earth, that while comets probably did make some contribution, but probably not more than about 10% of the water came from comets. And so when this seems, at least from my understanding of what I

learned 25 years ago versus now, this recognition that the water did come from from from meteorites that must have been growing and when it went sort of when did it really be understood when did the isotopic analysis of water on on meteorites be such that you could say oh that that isotopic abundance is an agreement what we see on our oceans i think the first papers i remember about that were probably from the 1990s or something i can't vouch that there were no earlier papers but well there were there couldn't have been many earlier's i would have heard about in 2000. Yeah, well, I think what happened was that this was at a time of a more general emergence of geochemistry as, you know, integral way of understanding our planet. And part of that

was the immense power of isotopes to tell you about all sorts of different things. So, you know, reasonably enough, people started looking at the isotopic composition of materials like like meteorites. I think the the hardest thing was to actually get samples of comets that you could yeah you could actually measure and so you know at first you know we had some material from one comet and then it was pretty easy to say well how do you know that comment's representative and you don't with one. Yeah but now I think there's at least enough material that uh enthusiasm for you know, a major commentary input as Wayne. And where does, and just so people know, where do we get the, I mean, we don't have comments here. You know, you hold your hands up. So where do you get the material

from comments? As near as I tell, you got to go out and sample. Yeah. And so it involves space-based sampling. I got to say, in light of that, that one of the fun parts of my life was to actually work on a Mars mission and talking with the engineers at JPL, you know, makes me reconno. consider that. Oh, yeah. Yeah. And they, you know, they talk about going and docking on a comet and sampling it the way you and I might talk about going to the five and ten. Yeah. Yeah. I've been, yeah, when I was at JPL, it really makes you want to grow up and be and be one of them. And it's really an amazing, you know, it's fortunate. It's also a combination of throwing lots of money and bright people together and seeing what happens. And it's, it's, yeah. One of, so

one of the other fortunate things. that about having oceans and continue to have oceans, which would be relevant for life, is the fortuitous fact that there were enough meteorites and comets bombarding the earth early on that oceans would have evaporated any early oceans, very, very early oceans. But by the time, these zircons tell us there were oceans, maybe 100 million years after the earth formed, already that bombardment had sort of gone, had gone away, which is kind of fortuitous accident. And it's related to the physics of the solar system, right? Yeah, so it's not like it stops on a Thursday, but rather there's a very high commentary or a meteoritic flux as the earth is forming.

And then it just kind of decays. So there's still, you know, if you go and look at a set of entry and volcanic rocks that are three and a half billion years old, you will find evidence of, you know, impacts. So they still go on and they're much larger than they are today, which we know probably more from Mars than we do from Earth because there are craters there in Australia, which is really something to think about. But you're right. The very earliest Earth would have been a very hostile environment, but two things made it less hostile. One was the solar system context was evolving. And then also very early on, the surface temperature of the earth came to be governed by the sun and greenhouse gases rather than the heat from below. If you go out and look outside your house today, the relative importance of sun and greenhouse versus heat escape from the interior to the temperature of your lawn, it's about a million to one. And so very early on, Earth became a planet whose temperature history was in no small part going to be determined by solar radiation and the evolution of greenhouse gases, principally carbon dioxide. Yeah, no, this period, well, and there was, I don't want to spend a lot of time about this late heavy bombardment issue, but there was a, you know, around 3.9 billion years or something. there was some thought that there was a period of a peak of bombardment and fell down after that

that's been an evolving subject i mean this is uh and correct me you know more about this than i do but the idea that somehow there was this major influx of of uh meteorites around 3.8 or 3.9 billion years ago originally came from as you know the materials that astronauts picked up on the moon And since they had been in several parts of the part of the moon that faces the earth, and whenever they looked at the detritus, they had evidence for a 3.9 billion-year event. This was interpreted in terms of this star fleet of meteors that was coming into the inner solar system. And there was actually a very influential model then published showing how, if you brought Jupiter and Saturn into so-called resonance at 3.8, 3.9 billion years ago,

it would send all this material from the outer solar system into the inner. And that was, you know, that was an important idea for a long time. There are people who think it's perfectly correct, but it is the case now that people think that that distribution of 3.9 billion-year-old dates reflects one big event and not a Starfleet. And the person who actually published the original model that I told you about has said, well, you know, I have to admit, I really tuned that model. And I had to really work on it to make it work at 3.8 billion years ago. You know, it still works, but it works a lot more easily if, you know, say it happened to 4.4 billion years.

So the question of whether or not there was a discrete and transient increase in the meteoritic flux, I think is very much under discussion. But I think to the extent that it did happen, it may well have happened before 3.8 to 3.9. Yeah. The reason I brought up, it's an aside, it's just important to realize that, you know, what we need, know is determined by what we can see. Sure. And sometimes in certain areas, you know, you develop picture based on one set of measurements, in this case from the moon, the astronauts on the moon, and there may have just been a big impact then. And it's easy to be to realize it or to forget that your influence selection effects influence you a lot. And and it's important, therefore,

to realize that when there's one set of data, you have to be skeptical. And, you know, I like to say to people, if I happen to have been watching a basketball game and a meteor hit and killed me and all the people in the basketball and archaeologists, millions of years are now unearthed us and they found me and a basketball player. And that was the only sample. They'd say, well, there's definitely two different species of humans that existed on the earth. But they would just be an accident of the, you know, of the surroundings. Yes, sample size is a useful thing.

It's a really, yeah, and it's important to realize, again, when we think of how we know what we know, that some things are limited because we have limited, you know, and the areas of physics I work in, it's great to have 10 billion events, but in particle physics at an accelerator, but sometimes you're subject to one or two or three or five events and you have to be to be wary, so I wanted to point that out.

The other thing that we learn about this time is not just that there was water, which is really important, but that the early Earth had lots of carbon dioxide, which is again something I think, I'm assuming everything I learned about the subject I learned from you. I don't remember where I did. You're either too kinder. I'm going to see you.

Anyway, but again, that the early, it was very, it just, again, fortuitous that the early Earth had lots of carbon dioxide in the atmosphere because the sun was 15% less bright at the time. And the earth would have been frozen over if it hadn't had a massive greenhouse effect due to that huge carbon dioxide in the atmosphere at the time. Yeah, no, that's exactly right. We standard models of how sun-like stars evolve suggest that they should become more luminous through time. And when you run that backwards, people commonly talk about the faint young sun paradox. How can Earth have liquid water when the sun is so dim?

And one way or another, the answer to that pretty much has to be greenhouse gases. And what's kind of cool is it's been appreciated now for a fairly long time that as you have more increasing solar luminosity, making the earth warmer, that makes processes that remove CO2 from the atmosphere that much more effective. And it turns out then that the greenhouse gases provide something of an unsteady thermostat. Yeah, exactly. earth which you know in some ways you know people always talk about the origin of life you know on yeah and other planets but what might distinguish the earth certainly in our solar system if not over a much wider extent is not just that life form but that it's persisted for four billion yeah exactly that's not a given yeah and goes much to the physical workings of our planet yeah the fortuitous

aspects of that related to the carbon cycle which is which is as you see say is determined by a number of things and acts as a thermostat for the earth. And we'll get to, obviously, you're going to get to life. But it is really remarkable how, how, how that thermostat and the persistence of life on earth when we think about frequency of life and intelligence and all these other things are very important because it's not something I want to dwell on here. But the fact is that intelligence, at least the kind of intelligence we're talking about, took four billion years to develop. And it's not clear that life may be prevalent in many places in the world in the in the universe but whether it survives long enough

uh it persists long enough for that evolution to take place is certainly not at all clear yeah um okay well before we get to to to life and i want to get to it soon and now there is this other aspect the physical aspect of the earth the fact that the earth has dynamics that lots of other planets in our solar system don't rocky planets play tectonics that the earth's surface, the crust has a particular characteristic, which again was, you know, in the history of science was relatively recently understood and first ridiculed when it was first proposed that the continents were moving around and were different forms, but now form an essential part of understanding of the history of the earth and life on earth. And maybe you could just walk us through that a little

bit, in particular something you point out that the plate technics themselves was essential in a way for also the early evolution of life. And let me let me jump and say one other thing that I meant to say earlier. This decrease in the bombardment of life on earth over the first 100 million years is really fascinating because when you look at what potentially may be the earliest forms of life, they occurred about as early as the laws of physics would have allowed. the bombardment to have stopped. And either that's fortuitous or it tells us something about the ease of life evolving.

But play tectonics themselves played a role in that. So maybe you won't. Yeah, I'll talk about plate tectonics first, but I will share one little vignette on how hard or how easy is it to make life. Years ago, I was out of meeting. And Stanley Miller, one of the real pioneers in chemical evolution experiments,

was giving a talk. and someone asking, you know, Stanley, how long does it take for life to begin? And Stanley sort of thought for a minute. And he says, well, he says, I think a decade's probably too short. And he says, you know, maybe a thousand, 10,000 years. And if you can't do it in a million years, you probably can't do it. Now, that may be right. It may be wrong.

But what it reflects is the idea that life may well not have begun as the result of inherently you know, unlikely things that just happened to happen, that life on Earth reflects a determinant chemistry that would happen on any planet that had the chemical and physical makeup similar to the Earth. So that's that. That's very important. And we'll get to that because obviously one of things people are interested in, we'll talk about later. And I want to talk about near the end is life elsewhere. And knowing whether life is ubiquitous and forms easily everywhere or whether we're unique. It's clearly one of the key questions that people want to know. I think many people like yourself and myself would think that we're unlikely to be unique,

but it'd be nice to have the empirical evidence. But anyway, let's go back to. Okay. So plate tectonics, as you said, is an idea that has really become convention, you know, in our lifetimes. It goes back to earlier in the century, through the writings of a German meteorologist named Alfred Wagoner. And as you alluded to in bringing up the subject, you know, particularly in the sort of academic centers of North America and to a certain extent Europe, people were scathing because they couldn't figure out a mechanism by which continents could plow through this basaltic crust. And it was really a series of observations, in beginning actually with geophysical work in World War II that was designed to actually identify German submarines and ended up identifying a mid-ocean ridge that ran through the Atlantic.

And then gradually through a series of observations, people realized that the continents didn't have to plow through the oceans, that the oceans were spreading apart and the continents were along for the ride. There are other places where the oceans were, you know, diving back down into the mantle. This is called subduction zones. And so between about 1965 and 1970, this went from heresy to a broadly illuminating view of how the earth works. And there's still research going on, but it's not on the fundamental question of, is there this convective engine? in the mantle that really determines what goes on at the surface. Now, if that's true, and it is, then the question becomes, was there always plate tectonics? Because as you know, no evidence for plate tectonics on Jupiter or Mars. Yeah. So it's not a necessary part of planet formation.

And there, it's a very active field of research. And it is one of these questions that, you know, if you wanted to induce a bar room fight among Earth scientists asking them when plate tectonics began is a good way to do it. And part of the problem is that the way it's often stated, you get the impression that on a Monday, four billion years ago, there was nothing like plate tectonics. And on Tuesday, the Earth looked modern. And that's ridiculous. It probably happened over a long interval of. time. I can imagine that plate tectonics, when it originated, could have been local and short-lived and then became more prominent. But most people, most people argue that something at least

broadly like plate tectonics, as we see it today, was in place more than 3 billion years ago. And that was associated with the growth and differentiation of continents. But it also provides something of a dynamic system for rejuvenating the earth surface. So carbon goes down into the mantle and is lost from the surface. And then volcanoes introduce it back to the earth's surface. And it's been argued by a lot of. of people with, I think, you know, for reasonable reasons, that it would be hard to see how life could sustain and prosper over long intervals of time unless you had this mechanism

of surface rejuvenation through time. Yeah, which is amazing, but we should, it's worth pointing out for people who like to think of carbon in the atmosphere and the earth and volcanoes versus as humans that that carbon cycle, which is incredibly important, happens over, you know, and I, again, I remember when my book, I tried to figure out the life cycle of carbon dioxide versus oxygen and a carb, you know, how long it takes that cycle to recycle maybe 100 million years for a given atom to go through the earth. And that represents the fact that volcanoes are producing carbon at a level of something like one, one thousandths or 10,000th, the rate at which we're putting it into the atmosphere. If you, if you, that's,

carbon cycle, I think it's something like 0.01 gigatons per year or something like that, or 0.03 or some. Yeah, I think the important thing is what you said. You know, I have talked to any number of well-meaning people who just cannot imagine that people have as much influence on the planet as these massive volcanoes in that. I call it the Little Ols Syndrome. Yeah. And in fact, you're right that humans introduce through, technological processes about 100 times as much CO2 into the atmosphere every year as all of Earth's volcanoes combined. So this is probably a topic for later in the discussion, but it illustrates that humans are not just bystanders in this. Humans are major players in the carbon cycle and other

cycles that sustain life and environments on this planet. And we and our production is, is somewhat similar to another event that you played a key role in unraveling, which is a Permian extinction, which I hope to get to. And so we'll get there. I hope. I always like when physics can be used for something.

So one of the ways I want to at least mention that one of the ways we can empirically prove for people who may not believe continents are actually drifting is magnetism. And it's a lovely, a lovely factor. So maybe you go through that for a minute or two. Yeah, so if you drain all the water from the Atlantic Ocean, you'll find that pretty much running down the center of it from north of Iceland down to Antarctica is this mountain range. And at that mountain range, new magma is coming up from the mantle and forming new oceanic crust.

and through time, that moves away, actually probably pulled by subducting crust somewhere else. But what happens then is if you look at the dates of that crust, it's very young, right in the ridge. It gets older as you go away from the ridge. And in the 1960s, two British scientists did a magnetic survey of the seafloor. And that you can do that because when volcanic rocks crystallize magnetic minerals in them like magnetite will actually form in alignment with Earth's magnetic field. Okay. So that's fact one. Fact two is we know that that magnetic field actually reverses through time.

That is what's the North Pole today, 200,000 years from now might be the South Pole. And so what, taking advantage of those two observations, these people actually mapped the distribution of, you know, the point, the way that the magnetic minerals were pointing as you moved away from the mid-oceanic ridge. And you see these strips of magnetic coherence, you know, close to the, close to the ridge. They show the North Pole going north, a little bit further away. They show it going south. And the only way that can happen is if the sea is slow or the sea floor is slowly getting larger from its source of that ridge. And, you know, you can actually use. satellite observations now to demonstrate that, you know, Boston is getting farther away from

London by about two and a half centimeters or an inch every year. Moves at the same rate your fingernails grow, I'm told. Basically, yeah. And yeah, this wonderful fact that the Earth magnetic field flips, which we still don't understand, and had I more time, I talked to you about it, because it related to the physics presumably of the molten core of the earth. But whether we understand or not, it happens. And it gives us another kind of chronometer.

And so it, yeah. And anyway, it's interesting. You could also measure that continental drift in a number of other ways with sophisticated physics experiments from gravitational waves experiments to CERN allow us to measure that two and a half centimeters a year. It's kind of a neat thing. And it's important to realize that I'm going to fluff over it, although we might get to it when we talk about life and earth,

that the motion of the continents was incredibly important that people, most people, a lot of people now know, but maybe some don't, that all the continents, of course, that motion has produced at times supercontinants, Pangaea and other things. And they've affected the evolution of life we'll get to in big ways. And there's a period of time. in the Earth now called Snowball Earth, which again, when I first learned about it, was controversial,

but is now accepted when the Earth basically froze over. And it's related to the albedo of the Earth and where continents were at the time. And I point that out also because when we talk about the possibilities of life elsewhere in the universe and planets elsewhere, people talk about habitable planets, which are mainly pamphets in a region of their sun where there could be liquid water on their surface. But I like to point out that since the Earth is a habitable planet, but there are times when it wasn't, it didn't have liquid water precisely because of the continents. And so it's, you know, it's nice to imagine that there's liquid water on these planets that may be in that zone. But since we don't know anything about the continents or their surface,

it's a far cry from being able to say we have any certainty that there's liquid water on those systems. Yeah. And we can talk about this more later. But, you know, I think we have good geochemical and geomorphologic evidence to say that there has been liquid water on Mars in the past. Yes. But it's very reasonable to think that that was transient. You know, that it happened fairly frequently four billion years ago and not very frequently afterwards. And that has real implications for how you think about life on another planet. But just to finish off the plate tectonics thing, you know, once you've established that the Atlantic Ocean is getting wider through time somewhere crust has to be destroyed because the earth is not getting

larger and you know if you just look at a map and look at the distribution of volcanoes you can see that they sort of ring the Pacific Ocean it's often called the Ring of Fire and those are all places where the Pacific Ocean crust is subducting you know beneath South America beneath North America beneath the Sea of Japan, things like this. And there are also places where it's pretty clear that two continents have collided. So India moved north, rammed into Asia, and now we have the Himalaya.

And so the explanatory power of plate tectonics is really quite astonishing. Yeah, no, it's, and it's important, and as you say, it's important, it's not just explanatory. utility, but also its impact on the fact that there's this interplay between life and the earth that goes in both directions. And so I want to now move to life. Another area where you've had, obviously, a huge impact in your research by merging biology and ecology and geology. And I want to talk

about that. We won't be able to give it its due course because I don't want to keep you here for eight hours. But although I'm fine with it. Anyway, the, so yeah, I mean, our understanding of the origins of life is still emerging. As you point out, Miller and Yuri did a very early experiment, which seemed, which was fascinating, although it would probably use the wrong materials. But it was first realized the first time, you know, life seems like a miracle until you discover it may not be. And one of the ways to discover that is that natural, that, that, that natural, that, that

prebiotic processes, chemistry, can produce a lot of things that you didn't think it could. And the first, I think it's fair to say, the first experiment that really shocked people was the Miller-Jurie experiment. So maybe you talked about that for a minute. Yeah, what, when Stanley Miller was a graduate student at the University of Chicago in the 1950s, was working with Nobel laureate, Harold Yuri and Stanley decided to do a fairly simple experiment. And that is he took a flask and put into it, CO2, methane or natural gas, ammonia, and hydrogen gas, which was his and Yuri's thought of what an early atmosphere might have looked like. Now, even at the time they did that, there were alternative views.

But when they did that, and then they wanted to simulate lightning going through this atmosphere, so they ran an electric spark through it. And as they did that, they started to see the surface of the flask becoming brown. And after a couple of days, when they looked at what was in the flask, they found amino acids, the building blocks of proteins and other things. And what that showed was in principle that. that the building blocks of life can be made under plausible planetary conditions by,

from simple chemical precursors. Now we've come a long way since then, but the principle still holds. And we have now gotten to the point where we can figure out how to polymerize those amino acids. So they start actually having some function like simple proteins. I was just reading this morning,

about some new experiments where, and this is sort of one of the Holy Grails of this field, people have been able to take RNA molecules and actually have them replicate themselves and they can diversify. You know, you're sort of knocking on the doors of biology when you have things that can replicate themselves, evolve, diversify, and function. Now, that said, we have come a very long way, even in the last decade, in insights into the origin of life. I don't think anyone in the field would say that we have a deep understanding of it yet. But the other thing that we've learned about, and this is where I think my work comes into it, is that more and more people who are doing these kind of laboratory experiments would like them to be relevant to,

what processes might have been like on the early earth. So guys like me who take boots and hammers and go out and look at old rocks can actually go a long way toward constraining what goes into those experiments. And certainly the most important thing in Stanley Miller's experiment was the absence of oxygen gas. And as we talked about at the beginning of this conversation, that has been confirmed quite strongly. In fact, life existed probably for a billion years or more before oxygen became an important constituent. And in fact, that's a wonderful introduction of what I wanted

to next in a way and also a wonderful introduction to early to our understanding of origin of life studies. But a very important fact is as you point out, there's been a tremendous amount of work since Miller-Yuri. There's still a lot of work left to do. But one of the things that has been understood is that the prebiotic chemistry does not work well if there's oxygen. That's correct. And that's really important. And I guess I think of it in my own kind of coarse and heathen way as just thinking of the fact that life is kind of controlled burning. And if there's lots of oxygen, the burning happens before the life can do it. And so maybe that's the way I tend to think of it. this oxygen, if there was a lot around, then there were energy available to make, you know,

the other chemistry wouldn't be around. Yeah, no, I think that's right. Oxygen will react with some of these early, early precursor molecules. And in fact, the kind of chemistry that gives rise to amino acids would not work very well because, you know, oxygen would combine with things like formaldehyde and that, which are the precursors of the amino acids. So yeah, I think if you're looking for a planet where you can originate life, the last thing you want to see is oxygen in the atmosphere. It's a great poison, which was a shock to me when I first realized it.

The interesting thing is, and I want to just jump, I mean, because I don't want to spend so much time in Origin of Life Studies, I want to talk about the work you've done where it really did happen. Life did originate on Earth and how can we learn about it. But it's fascinating that there's a question I want to ask you because more and more the understanding of how to not just take early molecules, but maybe polymerize them or at least form the early nucleotides have focused on an RNA world. For a variety of reasons, once it was realized that RNA could be both a replicator and a catalyst, it suddenly became much more reasonable to think of an RNA world as a precursor to a DNA world. and I don't want to spend a lot of time on that. So a lot of work has been focusing on could you, by prebiotic processes, create RNA, and on John Sutherland and his colleagues at Cambridge

have done a lot of work on that. But one of the things that interest me, because it sort of confronts what I used to think of as the preferred place of life to form, is that I was listening to John Sutherland talk recently and is in the chemistry that they're looking at, ultraviolet light plays a key. role, which would suggest that you're near, you need to be near the surface for that chemistry to

happen, whereas so deep ocean vents might not be the best place for that to occur. So I wanted you to throw that to you to see, because I'm sure you're more knowledgeable about than I am. Yeah. You know, when you talk to people interested in the origin of life, there are two communities, which I think are licensed to shoot each other on site. There are the people that you have just talked about who are wonderful people. Many of them are my friends and they're just amazing scientists who really think about information first. And the idea that RNAs could both carry information and be replicated and how function gets you around this chicken and egg questioner, which came first proteins or nucleic acids. And we are getting to the point, as I said, where

people are figuring out how under plausible conditions you can get RNAs that actually replicate themselves evolved to have new functions and that the other camp are people who think about metabolism that is you know how do you get energy and use it how do you get materials and use that and they are the people who like the idea of hydrothermal you sure regions because there's lots of energy material chemical gradients that they can use now there's a couple of things to be said i i think whichever one of these doors you go through the last common ancestor of living organisms had both yeah and i think the biggest problem in origin of life chemistry is understanding how either one of those systems evolved from the other or how they how they merged

and we're not there yet. Sure, absolutely. But the other thing to say, and this goes back to the environment, is I keep telling all of my origin of life friends to go to Iceland, because Iceland is a place where the mid-Atlantic grid, with all its hydrothermal vents, is above sea level. Yeah. And you have lakes.

So if John Sutherland and Jack Shostack and others would like lakes that wet and dry, if they would like sunlit or radiated environments, that is not something that precludes having the advantages of a mid-oceanic ridge. And the same thing is true. If someone like Bill Martin really would like to see these hydrothermal ridges as important places where metabolism could take place, that doesn't preclude chemistry about lakes that dry up. So I get most excited when I think about environments for the origin of life by thinking about an Iceland without oxygen.

And they're all, that's fascinating. That's a fascinating picture actually. But that's the key point that I mentioned earlier is that somehow the where is almost important as how you need to know both. And it's that challenge. And I guess because I've been writing on a lot lately, I've been thinking about it not only how emerge metabolism and replication. But the interesting thing is, prebiotically, you use something else as what you would call metabolism. You use something else as a source of energy to create the

materials that would replicate. But somehow, that had to shift to eventually not use prebiotic chemistry to have metabolism, but biological chemistry produces metabolism. And that shift to me, I think, is the most, is the hardest thing right now when I think about understanding. No, I think that that's exactly right. That's consistent with what I was saying. And, you know, I in some ways, I'm optimistic that, you know, in coming years, we'll get a lot closer, you know, particularly when I think of what we know now that we didn't know 10 years ago. But I think it is going to involve some meeting of minds on early environments where this could take place. You know, what is the role of clay minerals?

What is the role of iron minerals? You know, most of the proteins that are important catalysts in metabolism have metallic cofactors. And maybe that's trying to tell us something about what early metabolism was like. Yeah. Yeah. Anyway, it's a fascinating subject. But equally fascinating is actually looking at trying to learn about how that may have happened by looking at life on Earth.

And that's an area where you have another area where you have. have made important, well, groundbreaking developments. And that's looking at something, I guess, which is early life. I mean, trying to figure out that there was early life. If I'm not mistaken, the work you did, which you may have accidentally happened upon in Spitzbergen, is to realization that if looking at this stuff called shirt,

if you look at it, there are actually examples of really early life. I think it's called that a carrion life. I'm not good at names, which is another reason I couldn't do about geology. But I can't remember names very well. But that before a fossil, everyone thinks it's fossils, he trilobites and all these other nice things, that the big discovery is that there was lots of life before that. And you can try and follow it back and that there were micro fossils.

And they take us back maybe not just 500 to 700 million years, which I think is where your early were first illustrating. that, but maybe back to 1.6 to 1.88 billion years and maybe even to 3.8 or 4 billion years. So could you just take us through that? Yeah, a lot of my career has been trying to understand and fill that record out. And I have to be honest and say the first person to show that there was evidence of microbial life that long predated animals was my mentor, Elzo Bargorn. And I just thought that was fascinating.

You know, everybody knows there's dinosaurs, but dinosaurs, the oldest dinosaurs come along about 95% of the way through the history of life. And, you know, the oldest animals are not even 600 million years old. And here we have this planet that's 4.5 billion years old. And so if you look at comparative biology and, you know, trees of life or phylogenies, so-called, that are based on comparisons of molecular secrets. in living organisms, they suggest that animals should be latecomers and that most of the history of life is microbial. So then the practical question is, that's a nice idea, but how can you actually study that in the rock record?

And what we've found, as you mentioned, is that there are certain types of rocks that are particularly good at preserving actual cellular fossils of ancient life, both ancient bacteria and, ancient nucleated cells, you know, protozoans, algae. And they carry us back billions of years. Also, it turns out, you know, when we think of reefs, we think of coral reefs, but long before there are any animals, you know, microbial mat communities built reefs. And we have reefs that go back three and a half billion years built by bacteria. And they're all over the place. The seafloor was covered with these. And then third, sometimes you don't get the preservation of a cell or a body, but actual biomolecules.

I'm fond of telling my students that when you die, your DNA and proteins won't last very long because they're too good to eat. But the last thing of you that will be available for future generations to ponder is your cholesterol. because lipids and these sterols can actually preserve over long periods of time. And again, we find these preserved in the rock record well before animals. And then finally, you know, microbes may be small, but collectively they can influence the chemistry of the earth. So we can use isotopes of carbon, for example, to, you know, investigate the history of photosynthesis. Could I interrupt you for a second?

Because I'm wondering whether I don't know if it was your research that would put it to this, but it's looking at isotopes of carbon that can be very important to understand the early history of life. And I would and people may not realize why. So if you could just, am I right that you were some of your early work? I played a role in some of it. Again, you know, most of us have stood on the shoulders of giants. Yeah, sure. Newton was probably a little bit too humble. No, I don't think he was humble.

he was joking he was talking about a dwarf one of his competitors and he was he was a competitor of someone who was of he was never humble and he was never nice just so you don't don't know don't get the wrong idea about newton anyway go on yeah so it turns out that like oxygen carbon comes in three varieties about 99% of all the carbon on this planet has six protons and six neutrons that's carbon 12 about 1% has an extra neutron called carbon 13 and then parts per trillion have two neutrons they're called carbon 14 which is radioactive and breaks down you know on scale of thousands of years so it's very good for dating archaeological objects not so much for the earth now it turns out that when organisms photosynthetic organisms take in carbon dioxide for photosynthesis and you know make it into

sugars and the other materials of your body, they actually discriminate so that they preferentially incorporate carbon dioxide that has carbon 12 relative to carbon 13. And the distinction for most organisms is about 25 parts per thousand. Again, things that can be measured with a mass spectrometer. So we can go back through time and look at limestones and look at the organization. organic matter in them. And if you go to these rocks in Spitzbergen that I talked about, or these rocks from Southern Africa behind me, again, there's 25, 28 parts per thousand difference between them.

And that's easily explained by saying there was a biological carbon cycle driven by photosynthesis. And in fact, you can do that through three and a half billion years ago. And even perhaps earlier than that. So that the carbon actually tells us, That we have had, you know, basically we run out of a record to look at before we run out of evidence for a biological carbon cycle. So life must have begun early. I won't go into it now, but that carbon isotopic record can also be used to tell us about the workings of the carbon cycle,

particularly with the burial of organic matter that is linked to the formation of an oxygen-rich planet. So, yeah, isotopes are. Yeah, I want to get to auction, but they're incredibly important. And I guess I'll jump through the details of the Spitzberg and then seeing it as you say, 1.6, or 1.8 or 3 billion in Australia and these old rocks you're looking at in Africa. I want to do ask you, so where does the controversy stop? I mean, I've heard, first I've heard about 4 billion year old evidence of micro fossils. I just was reading about 4.28 billion-year-old evidence in Quebec.

Is that accepted? Is that controversial? What's the deal? Yeah, it's controversial. I think that most people would agree that in actual set of, you know, well-preserved sedimentary rocks that are 3.5 billion years old on several continents, you've got both physical and chemical evidence that suggests, you know, you had a microbial carbon cycle,

and microbial sulfur cycle. So early life was a going thing at the time. Now you can go back to metamorphose rocks, metamorphose sediments. You know, they've been subjected to high temperature and pressure. And they still have carbon isotopes that suggest that there might have been a biological carbon cycle, although you just don't have quite the confidence as you have in these better preserved sedimentary. Well, that's, there's some little bit of carbon that's seen in zircon again, right?

Is it? In one zircon, there is one bit of graphite, just carbon in it. And first of all, that is an analytical, turdiv form of course. It's just amazing that you could do that. And when you look at the carbon isotopes of that, they are similar to the carbon isotopes of organic matter made by photosynthesis. Now, the Miller-Yuri experiment actually fractionates carbon isotopes. So there are ways of getting that signature in isolation that don't require life.

And in fairness, the people who wrote the paper were very honest about saying that. So again, it could be, who knows, the stuff from Quebec, there are questions of its age. There are questions of how the structures that they found form. I don't think they particularly advance the question one way or another. But it's hard. When you have very few rocks and they have been buffeted by time, it isn't as easy as going out to the seashore and picking up shells. It's just a whole different.

Yeah, once again, in selection effects, in fact, we have very, the older back we go, the less evidence we have at least here on Earth, which, you know, maybe we'll be able to find lots of, of more samples elsewhere, but I hear on Earth rocks that are that old to tell us things. Just so we make it clear, that Zircon with that carbon was dated to what age? Just we didn't mention it. 4.1. 4.1 is my understanding of that. So that's, so the this is where we get to that statement that I

said earlier, which is surprising. We know with confidence now that our life goes back to four billion-ish years, whether it's four billion or four point two billion years, but it is amazing how close to the, not only the formation of the earth, but to the period where the earth became even possibly hospitable for life. And that speed is something that anyone who looks at it, I think, is surprised at when they first see that. When you think of at least we grew up thinking that life was hard and rare, and that's why that statement of Miller is kind of interesting because it'll be,

and we won't know the answer, of course, in some sense, until we discover how easy it is for life to form, not just here, but elsewhere, which we'll get to. Yeah, no, you're right. I mean, what we know from the geologic record is that Earth has been a biological planet for most of its history. And that I think does somehow bias us towards thinking that, as I said earlier, that life could originate relatively rapidly given the right conditions. It doesn't tell you how common those conditions are in the universe. It just says that on Earth, they seem to have facilitated.

and early evolution of life. And then what we can see as we go up through time, you know, about 2.4 billion years ago, we start seeing oxygen, which relates to photosynthesis. A little bit after that, we start seeing evidence of nucleated cells. And, you know, those, of course, through time, will make possible plants and animals. And so the bottom line from the geologic record

is that our modern Earth, in terms of of both its biological diversity and its environments that we see is actually something that evolved over a very long period of time and things that are, you know, even remotely like our modern earth have only characterized, you know, the last 10 or 15% of our planet system. Yeah. And in fact, okay, and that's where I want to go next to this other surprising fact, of how life has changed Earth and the most obvious example, I guess is oxygen, where there has been again, it's fun for me because I last sort of dip my toes in this water 25 years ago and then to come back and see the how much knowledge there's been in terms of

that period of what's called the great oxygenation event and really how great it really was and the history of life of oxygen and earth, which I think is important. to get to where I want to go next. How would you feel about taking a break now and doing it later day or another day to do that last 45 minutes? So I wanted to find out about your time. I think it might be easiest if we, I'm happy to talk for another 45 days. It's a lot of fun.

It might be easier to schedule it and do it another day. I think so. It would be easier in my life. But I want to schedule it pretty soon. So while we're fresh. But I think this is fascinating. And again, I hope you're enjoying it. I hope that you're finding it.

Yeah. Yeah, it's fun. This will be amazing. It really is fun. And it'll be, I think, really interesting for people that won't have ever heard this kind of detailed stuff. Well, welcome back, Andy. I'm sorry we had to take a break last time due to circumstances beyond my control, at least. And I really appreciate you coming back because the story that we're talking about is fascinating.

And it in some ways gets more fascinating. Because when we last spoke, we were in an earth, which was. which was still essentially oxygen-free, and life had begun, but just the beginnings of life. And the thing that really changed with life, where life changed the earth, and then the earth changed life is the rise of oxygen in some sense. And I want to reiterate something we said last time, which I mentioned, which was a sentence in your book, which really hit me as, as we... really important that prebiotic chemistry doesn't work in an oxygen-rich environment.

And therefore, no oxygen, once again, was very important in the early Earth. But then, of course, it changed. Now, this is another area where it seems to me at least that the understanding has changed somewhat over the last 30 years or when you and I, when you were first teaching me about this. And that is the history of oxygen in the earth. I had thought by two billion years ago, oxygen was almost at its current levels.

But my understanding is now that it's not. And let's talk about the way we know, one of the many ways we know oxygen wasn't in the early earth, which is iron formations. So maybe you could talk about that a little bit. Yeah, there's actually a variety of geological signatures that tell us about oxygen history. One of the first ones that scientists started talking about

is something called iron formations, which are sedimentary rocks that consist mostly of iron minerals and silica or chert, flint if you will. That's a type of rock that cannot form in principle in modern oceans because its formation requires that iron be transported through the oceans in solution, and that can only happen when there's no oxygen around. And so it's very interesting that iron formations are part and parcel of sedimentary successions

before about 2.4 billion years ago, and then it slows down considerably. Now, there are banned, one thing, these banded iron formations, does that indicate that there was fluctuations in oxygen at early times as well or no? Probably not. There's a variety of ways you can get the sort of banding on levels from, you know, millimeters to centimeters to meters that you see in these rocks. And although there's every reason to believe that oxygen levels may have fluctuated on the early Earth, both in time and space,

I think there's pretty much agreement that only beginning about 4.4 to 4.2 billion years ago, did we have a permanent transition to at least an atmosphere and surface ocean that contained O2. Okay. Between you say four point, what time again? Yeah, 4.4 to 4.2. And this does look like it's something that, you know, tried a couple times before it took permanently. So, you know, even as much as little as a couple of years ago, you know, people talked about this as though it was something that happened on a Tuesday. But in fact, it looks like we have this fluctuating the appearance of some oxygen, then it disappears, then a little bit again. And then finally, around 2.2 billion years ago, we seemed to enter a new state of the system that persisted today. Okay. Yeah, okay. That's why the reason I ask, I think you said 4.2 and you meant 2.4.

2.4, sorry. Yeah, yeah, that's okay, okay, it was 2.4 to 2.2. Before that, we were definitely auctioned for you. There was also, I was always fascinated when I was a kid about pyrite. And pyrite also plays a role in our understanding of this as well, of the oxymes. Yeah. And again, this goes back to something we talked about last time, which is just the treasure trove of information that you get from the isotopes of different elements. And in this case, it's sulfur, which is, of course, an important constituent of pyrite,

which is ion sulfide. Again, it turns out that there are three stable isotopes of sulfur that can be measured with high-resolution mass spectrometers. And rocks older than about 2.4 billion years ago have a very interesting signature to them that is thought to have been imparted by photochemical reactions in the upper atmosphere in the absence of oxygen. Oh, I see. And by 2.2 billion years ago, that signature is gone, and it remains gone to this day. So it's an independent signature, you know, independent of the signature from iron. Yeah, well, it's always nice to have two independent measurements of different, that are consistent. It gives you confidence.

Yeah, in fact, there's four or five, and they all give the same answer, which is good. Now, there was still, of course, life without oxygen was still vibrant. And you talk about bacteria and its ability, I mean, oxygen is useful for oxidizing, obviously, but, but, and for basically taking a lot, by taking electrons, it allows life to to basically have more energy than it would otherwise, by a large factor. But bacteria could could either use oxygen or in these other environments, hydrogen sulfide, right? And so there's this interplay between environments. Yeah, I mean, there are, for organisms that like us, ourselves are heterotrophes, that is they take in organic carbon and then oxidize it to gain energy. We use oxygen to do that, but there are bacteria that use sulfate, there are bacteria that use iron, there are bacteria that use nitrate.

And so as oxygen started to accumulate in the atmosphere and surface ocean, the inventories of things like sulfur. and nitrate also increased. So you just have this broadening of the metabolic possibilities in the first instance of bacteria. Ah, okay. But then, but then, as you say, 2.4 billion is called the great oxygenation event. Although I now learn it wasn't so great, right? I mean, it was great, but it wasn't so great. It was an okay oxygen event. That's exactly right. I smile because one of my old teachers from whom I learned a great deal was a wonderful geochemist by the name of Dick Holland. And Dick used to show the history of oxygen on a log scale so that the GOE at 2.4 or 2.2 looked huge.

And then the other 99% of the incentive today looked very small. But you're right. And I think that an appreciation of the fact that when the great oxygenation event was over, we still had a long way to go is something that has because. fairly widely understood in the last 20 years or so. Yeah, no, that's what I'm saying. Before, when we first talk, which was about this, which was more than 20 years ago or at least 20 years ago,

I was under the impression that things went up quickly. And yeah, and now I understand it sort of didn't. It was at the 1% level for a long time. Yeah, something like that. And then there's a second event, you know, which interestingly enough, as we'll talk about, coincides with the rise of large, modal animals. Yeah. And that's that's much, much younger. And that really brings us into a more

modern state of the world. Yeah, we'll talk about that because there's energy play. I think, I mean, the chicken and egg. And I was going to ask you that question. I mean, well, I'll wait to ask you that question because I want to, I want to understand. My understanding is this is another area where you, your work played a key role, which is trying to understand the call how the ecology of things and how and what what stopped what stopped things oxygen for building up and when and why it began to build up when it did this competition of of cyanobacteria and so could you talk about that a little bit yeah this is an active area of research and and i've made some contributions but so i have many other people um i think one interesting idea which i credit the lab of don canfield in

Denmark for is the idea that there are other kinds of photosynthetic bacteria that do not get their electrons from water and do not give oxygen as a byproduct. And if you have a lot of alternative electron donors, which could be iron, could be sulfide, could be, you know, H2S, hydrogen gas, if you have a lot of that and not much phosphorus, which is a major nutrient that limits primary production, these other kinds of photosynthetic bacteria are likely to be the ecological dominance. Under those conditions, not much oxygen will be produced biologically. But once you go past a sort of tipping point where you run out of alternative electron donors before you run out of phosphorus, then cyanobacteria will come to the fore and they will have the potential to produce enough oxygen to start accumulating in the atmosphere. And so there's two things then going on.

One, you need biology to make Earth's atmosphere oxygen rich, because the only real source is what we call green plant photosynthesis, but is more properly thought of his cyanobacterial photosynthesis. But how much of that goes on and whether or not these organisms will be ecologically competitive depends a lot on phosphorus. And phosphorus, in the first instance, weather's from exposed continents and volcanoes and enters the ocean.

So one of the things that looks like is happening now, and this is something that's evolving on almost real time, is the idea that only shortly before we see the GOE, we have evidence that large stable continents, had emerged. And so that would increase the phosphorus supply, potentially tipping the balance in favor of oxygen-producing photosynthetic organisms. Yeah, I found that fascinating, the idea that it was far, you have this rate-limiting step and you have enough phosphorus, boom, you get the oxygen-producing bacteria, cyanobacteria, and the fact that it was related to continents.

It kind of interests me because you think of life influencing the earth, but in this is a clear case where the earth is influencing life. And it did remind me of sort of in some sense this Gaia picture of sort of earth and life is coupled together in a really strong way. Yeah, well, there's no question that earth and life influence each other. And I think there's also no question that this pivotal event in Earth history, the initial rise of oxygen, it takes both physical and biological processes to happen. not that one dominates over the other.

Yeah, no, that's really interesting to me because at Ann hit me that I used to think it was a natural consequence of sort of of early stages of photosynthesis that oxygen would rise, but this competition that you can get electron donors or electron takers, I should say, from other parts of the environment is really kind of interesting. Yeah, I mean, one of the things that people notice in, you know, today's environments, there are certainly places where sunlit waters have no oxygen today. And in those environments, when there are other electron donors present, cyan bacteria don't compete very well.

So it's sometimes easy to think, well, all you have to do is evolve oxygenic photosynthesis and you're off. But oxygenic photosynthesis could be local and transient in many environments until we have this couple change in the environment. Well, you know, that'll come later. I want to talk to you later about thinking about life elsewhere. And once again, as I said earlier, we should be careful when we talk about habitable planets being habitable. There's not just the creates of liquid water, but by this argument, if you had a water world, which had no continents, that might be an impediment to to at least producing advanced forms of life because you wouldn't

have those oxygenation events. Well, yeah, that's, I mean, there are other ways of making oxygen under other conditions, not on Earth, but, you know, water worlds might provide abiotic sources of oxygen. So there's, there's lots of permutations. Yeah, exactly. And the point is, we probably don't know. I mean, as I often say, the most interesting permutations, I'm sure we haven't thought of yet and, and, uh, of what's possible. And we'll talk about that when we get to life. But around, around the time of the Great Oxygenation event is when eukaryotes began to emerge. Is that true? Yeah.

And one of the reasons for that is that fundamentally eukaryotic cells, which are cells with nuclei, like in our own bodies, have a little organelle called a mitochondrian, which is where respiration actually happens. And it is now fairly clear that the mitochondria evolve. from a once free-living bacterium that was, you know, incorporated into a host. So the last common ancestor of all living eukaryotic cells represented this merger between a host cell in which a group called the Archaea played a large role and this mitochondrial ancestor. And so that would have only happened once there was oxygen in the atmosphere because, you know,

these mitochondria are fundamentally respiratory. Yeah, they're oxygen, and now in our current cells, they're where the oxygen, all the action happens with oxygen. That's right. Taking in its usage and now that might, so that kind of engulfing, that kind of symbiotic engulfing or may be called cannibalizing, if anybody want to talk about it.

We talked about Lynn Margolis, you talked about in the context chloroplast, I think. But did she all, I always thought that she, that, that the mitochondrial merger was, was also her, but it was someone else? Yeah. Well, yes, Lynn did talk about both mitochondria and chloroplast. You know, in fairness, both of these had been raised earlier, although it's not clear whether Lynn actually knew about this turn of the century work done, you know, in part in, in Russia. And in any event, she did talk about these in the then emerging language of cell and molecular biology, which was a language that earlier generations didn't have to work with. And so, yes,

now, Lynn was very much an advocate of the idea that mitochondria were symbionts. Now, so you've now got these mitochondria and eventually have multicellular systems. But the interesting thing that I wrote down here which surprised me when we talk about the emergence eventually the emergence of animals which which I mean well I'll ask you a question now because it maybe it's obvious to everyone else but it occurred to me and I thought gee that must be true you couldn't respiration releases I think somewhere between 37 and 43 times as much energy as photosynthesis per per molecule is that right well respiration relative respiration using oxygen. Using oxygen. It gives a lot more energy than respiration using anything else or fermentation

or any of the alternatives of being a heterotrope. So oxygen, yeah, using oxygen and respiration really gives you a leg up in gaining energy from taking inorganic water. Well, saying a leg up is appropriate because what I was going to say to, I mean, it's, unless you, it's clear. It's not an accident. It seems to me that animals emerged. You can't. have you you can't have animals in some sense in building structures that seem to me require a lot more energy without a source of energy and until you have oxygen you don't have that source of energy so it is true to say that animals literally couldn't exist larger than small single cell or maybe multicellular organisms you couldn't have things with backbones and you couldn't have the kind

of structures you need which clearly take a lot more energy without oxygen probably not I mean, we do know there are some, as you say, tiny animals, things that are 200 microns long and 10 microns wide that can exist with little or no oxygen. But yes, I don't think you would see a Tyrannosaurus unless you had the kind of energy that only oxygen can supply. Yeah. And the animals, so you went from bacteria to algae to some extent. And algae were even more efficient producers of oxygen, right? Well, it's interesting that if you look in the oceans today, where there are very few nutrients, like the central part of the oceans, cyanobacteria are still dominant.

But where you have more energy, you have eukaryotic algae being dominant. And I think there's reason to believe that the succession that we see in time from a world that for three billion years was dominated by bacterial photosynthesis, to a world that really only came into being around six or seven hundred million years ago in which algae are major primary producers. That requires that there's more nutrients. And so one of the ideas we've put forward is that this is another jostling of the phosphorus cycle. And that that then has, A, it produces more.

the algae takeover in at least coastal environments, we have more oxygen, more food. And together, those two things provide a new world in which large heterotrophes like animals can do well. And it's sort of a feedback because more food, more algae, more algae, more oxygen. And it continues that way. It's sort of a positive feedback. And it's sort of a positive feedback. Yeah, that's really important because sometimes people have hypothesized. things that could lead to change in the amount of oxygen. But unless you have something that pushes you into a new steady state of the system, as soon as you relax that influence, you go back to where you were. So you're absolutely right that this positive feedback is a key thing.

And so oxygen achieved its current levels or close to its current levels. You see about six or seven a million years ago? Well, it becomes a lot closer to today. So, Having had, you know, what, a billion and a half years or so in which oxygen was maybe 1% of today's levels, you go up at least to 25, 30, or 40. And then most people seem to think, and again, there's four or five lines of evidence that suggest this, that oxygen reached more or less its current levels probably around 400 million years ago, something like that. Foreign rate. Okay. Now, we went for this world of dominated by, well, bacterial world to world with algae, but it's not fair to say that, I mean, I was going to say a world dominated by that, but in fact, you present a number, which is kind of, now I'm always going to remember, that is it true that in the current world, I think you said, there's 30 tons of bacteria for every animal? Oh, yeah. I always tell

my students that we are guests in a microbial world. Yeah. And that's true on. so many ways. Only bacteria have the diversity of metabolisms that allow them to really run ecosystems that replenish themselves through the carbon and sulfur nitrogen cycles. And that, you know, if you look in your own body, you have at least as many bacterial cells in your body as you do animal cells and they play important roles in everything from development to the working of your immune system. Yeah, I think we always think animals are important because we're writing the history, but animals were added to ecosystems on Earth that are fundamentally microbial in all of the circuitry that runs the ecosystem. Yeah, so it's fair to say, while in some ways we've

changed the world in many ways, and we'll talk about how we're changing it, we still are little peaks above this vast background of microbial. life that's been around for almost as long as life's been around. Yeah, basically. Now, but there are, let's talk about the peak. So I want to move to, as we think about the animal world, to another place you talk about, with great love. And it's a place I've heard about and I can't wait to visit.

It's mistaken point in Newfoundland. This important, well, let me, before we get that, that's 565 million years ago. And you talk about these weird and wild animals. And it does look very science fiction like when you look at the fossils from there. But before that, between the rise of oxygen and then is this snowball earth time, which we talked about briefly before. And I don't know.

I think I asked you this when we first talked about this years ago. And I thought, oh, this is something else I'm coming up with. It's either wrong or I'm sure other people have thought of it. but snowball earth was a dramatic event because it separated the atmosphere from what's inside. And it also clearly killed off a lot of organisms. Okay. But I've often wondered whether this explosion, which starts in this Edicarian world and then goes to the Cambrian explosion, whether, you know, whether, well, the way to put it is disasters or crises on Earth,

which get rid of vast populations, in some sense, produce an evolutionary opportunity for other things. So the question is if there hadn't been Snowball Earth, would this kind of transition and this explosion of new kind of life happened? Or was it possible because of the dramatic impact of Snowball Earth? Yeah, that's a good question. And I think it's fair to say there's variance of opinion on that. And I think the variation arises because the last messages of the snowball earth ended about 630 million years ago and we then see large animals about 55 million years later. So the question is, can I really say that something that happened 55 million years later is directly dependent on this other event? Did it influence life? Absolutely. We know that stuff. groups including early animals must have survived that event and as you say they come out on the other side in a world that is really new in terms of both their physical and biological

surrounding so it may well have played a role i don't think we have any detailed understanding of precisely what that role might have been now okay that's good okay but now we We have these sort of semi-exposureion of interesting animals. You see it mistaken point. And you talk about this sort of interchange of carbon and oxygen and the kind of animals that were there and how they're getting energy, how they're metabolizing, and how they're exchanging carbon and oxygen.

You want to talk about that and the fact that have to be thin. So you want to explain that. Yeah, the animals that we see in the so-called ediocry period, as you say, they are very unusual. They don't map well onto the body plans for animals we see today, at least not in a detailed way. And when you look at them, they don't have a mouth and a gut. They don't have lungs or gills. So they must have gotten their food either by individual cells on the surface, you know, just gobbling bacteria in or organic particles or by the absorption of dissolved organic matter.

And they must have exchanged gases by diffusion. Now, it turns out that actually describes to a T, one tiny group of animals today, or one group of tiny animals called plaque of zoa, which are, you know, just a couple of millimeters long, not much more than an upper and lower surface with some sort of gelatinous material in between. But in fact, that might be the last vestige of what was a predominant type of organization in early animals. And these placas, oh, if you look at where they fit on the tree of animals, they're right

in the right place to be right near the bottom of the tree. So I don't think we're looking in this early record of animals of something that represent an independent origin of complex multicellularity or anything like this. Rather, it looks like this is, you know, the first major radiation of things that we would call animals. Very few of those will actually survive very long, both because of some physical changes that I think may have. caused extinction as it happens episodically in the age of animals and also because we are going to have the radiation soon thereafter of animals that are really good predators and things like that. Well, okay, so this first radiation of these weird animals of the, and I'm glad you told me how to pronounce it. I always pronounced it at a carrion or something, but how do you pronounce that again?

Ediacaran. Ediochran, Ediochran, Ediochran. I had to see in the wrong place. Okay, good. But then you have this, what looks like a Cambrian explosion, trilobites, and the world changes. And so the transition from one to the other occurs, why? Well, again, that's something that people argue about. It is interesting that the world of these weird and wonderful animals goes right up to the end of the Ediachran period.

And there's very limited evidence for, you know, complex, modal organisms, animals at that time. And then once you get into the Cambrian, you see very little of these early ones again. And there's reason to believe that there were some physical perturbations at that boundary that may have actually extirpated them, at least in part. Was that one of the great extinctions or no? I don't know. Not one of the ones that's generally talked about. But it does look like something may have happened. And at the same time or shortly thereafter, you have this radiation of things that have

a front of back, the top and the bottom, you know, organizations that we're more familiar with. Things are motel. We have some of these are carnivores, so they're going to be eating other things. And just the whole ecological and functional dynamics of animals takes a step forward as we go. into the Cambrian world. And for the first time, we see body plans that are still familiar today. You mentioned trilobites and the arthropods. We see mollusks coming in. Basically, the Cambrian period is the time when nearly all of the basic types of body organizations we're ever going to see in animals take shape. So it's sort of the real precursor of the modern world in a sense. But could,

Could the car, I mean, could it, the fact that they were carnivores for the first time, could they simply have also eaten a lot of these other, could they have just, is that one of, I mean, could it not, could it be simply having the reason these other ones disappeared as they were good food instead of life plans change? It certainly may have played a role, sure. Yeah, the problem is that there's very little temporal or overlap between the two. Okay, so. Okay.

Now, you, there's another transition we'd talk. about the green world basically when now you have plants beginning to you know when you have continents up and you have plants beginning to transform the world and and and and colonizing land and changing changing things that happened around that time was it was a little bit later probably started around 500 million years ago and things that you and i might want to call a plant certainly existed by say 420 430 million years ago but not before that there was no, it wasn't a green world. If you look, if you were in a spacecraft coming in, there were continents,

but you wouldn't have seen green. Well, you would have seen little patches of green or blue green because there were microbial mats in wet areas on continents, probably, you know, as long as there have been continents. Yeah. But remember that, you know, in a sense, plants are green algae with a college education, basically. And they, you can't have plants until you have not only, green algae, but green algae with the kind of ability for development that allows you to make

these more complex structures. And that, you know, took some time to come in. But most molecular clocks would estimate the time of origin of some of these features suggest that, you know, complexity was coming to the green algae on more or less the same time scale as it was coming to animals. and eventually that ended up having some green algae that could exist on land. And, you know, it's important to note that soon thereafter, we also get animals that could live on land. Which is now essentially the modern world. And I want to move ahead because, I mean, and of course, we cannot,

and I think you talked about it once, we cannot mention the animals in the modern world without mentioning dinosaurs. Because, you know, they're the interest when you think, about early life, especially for kids, but for adults too, dinosaurs in a, in a, which began, and dinosaurs emerged around the same time as plant life? No. In fact, dinosaurs are fairly newcomers. They, the oldest dinosaurs, I would say, are about 240 million years old. And what I've always found interesting is that when you look at these terrestrial animal communities that existed between about 240 and 200 million years ago,

there's all this diversity and most of it is actually extinct groups that are related to crocodiles. Dinosaurs were just one of the gang, nothing special, nothing pronounced. And then there's a major extinction 200 million years ago, and most of the crocodile-dile relatives and other groups disappeared, dinosaurs survived and that was key to them becoming important and of course that it's fitting that they should you know die by the sword that they will because it's been 66 million years ago another extinct thing wipes out of the dinosaurs. Now you've you've done this segue perfectly for me because I want to focus on distinctions which again I keep touting you but I'm going to tell you again

it's an area where you've had a huge impact and not the dinosaur extinction. Most of us who think about extinctions know about the dinosaur extinctions because we know about the big comet or meteor or whatever you want to call it that hit in Chixilab and destroyed the dinosaur 66 million years ago. But that was pittance compared to the extinction that occurred, if I'm right, between 251.941 and 251.880 million years ago. Yes, you're very precise. But you're, I mean, I wouldn't say it was a pittance. The 166 million years ago was a major event in the history of the life. Sure. Sure. The largest mass extinction that we know of is this one at the end of the Permian period around 252 million years ago. That's it, it's at least estimated that as much as 90% of all animal species in the oceans disappeared at that time. It's, it's, which is amazing. And but to me, and of course, it's a, it's, it's

that may carry a more important lesson to us. I mean, the dinosaur one carries a lesson, which is we should be looking up for asteroids. NASA should be looking for asteroids, and that's a very important lesson. But the lesson that comes from the Permian extinction is, I think, a more significant lesson. And I know you agree partly by reading what you've written,

but I want to talk about that because, you know, the many people, I mean, this stuff is fascinating, but many people may say, oh, so what? Well, the point is that that we let these are, history gives us many lessons. And people have heard me say this before, but my favorite quote of Mark Twain, I think,

was history doesn't repeat itself, but it sure rhymes a lot. And so the Permian extinction is a major extinction. First of all, why was I able to be so precise? Why don't you answer that question? Well, two reasons. One is that there are some beds, particularly in China, where this event is captured in fairly great detail. And I've been to one of these places where you start climbing this cliff and it's full of all this Permian Marine life, lots of diversity.

And then you get to a point where you can put a knife blade. And at that knife point, all of those things disappear and you never see them again. really quite stunning to be there. And geology cooperated in this region because it was a time of active volcanic activity. And so we have some volcanic ash beds, which can be dated using our friends, the zircons that we talked about earlier.

And there's some just before the extinction. There's some just afterward. And that's what constrains with timing. Now, this is, I am correct, that this is sort of, I know you're going to deflect, but your work in the sense that sort of isolating that, and thinking about not just the extinction and at this point in China, but what could, what could have caused it? Well, I won't deflect this one, but one of the things that we did was it turns out there are some very unusual carbonate limestone textures associated with this boundary. And when I started thinking of looking at them and thinking about them, I was taken by the fact that they were similar to things that we see more commonly in records of the early Earth. And so we started thinking, you know, maybe there was a lot of CO2 came into the atmosphere at that time. So my friend Dick Bombach and I literally just spent three months in the library, in the library, reading about.

every experiment in which animals were subjected to a rapid increase in CO2 that we could find. And it turns out there's some generalities. And then when you sort of make up a list of features that should make a species more vulnerable or less vulnerable to increase CO2, the actual pattern of extinction at the end of the Permian matches it very well. So we now know that, in fact, the main producer of that carbon dioxide was massive volcanism. But I think we can probably take some credit for maybe being the first people to say, hey, you know what? If you put a lot of CO2 into the atmosphere rapidly, that's a bad day for life.

No, it's profoundly interesting. And again, I love learning new things that have changed our understanding and it may have an impact. And this volcanism is amazing. I mean, it's from Siberia, right? And the amount of, it's hard for people to realize the scale of volcanism, a million cubic miles of, so that's, put in that in perspective, maybe that doesn't doesn't do things for people. There's enough. If you had two kilometers of volcanic rocks over pretty much the entire area of the 48 United States,

That's what we're talking about. Yeah, we're talking about them. It's a million times larger than any volcanism, and any human being has ever experienced. And the fact that it was immense is remarkable. It happened as far as we tell once, I guess, in recorded, at least in the history of animals, maybe it happened at a time when it wouldn't have impacted

so much before. What caused such a, I mean, did it only happen once? Well, no, there are, there's a whole clobled, class of phenomena that geologists talk about called large igneous provinces or lips. And it is the case that every once in a while, and once in a while is the order of every 30 million years or so, we do seem to have these massive outpourings of lava. We know they come from within the mantle and are not closely associated with the plate tectonic processes that we talked about earlier.

Precisely what gives rise to these is something that people still argue about, but it happens. And I think there are, you know, some are larger than others, some are smaller than others, and also some take place at a time when the rest of the Earth system might make it more vulnerable than it is at other times. And so this is not a unique event. It's not the only event to cause major extinction. The same thing happened 200 million years ago, which is when dinosaurs survived and other vertebrates didn't.

So it is a recurring feature. Yeah, but it was, but yeah, well, it's recurring, except that one 90%. I mean, that's none of the other things that have happened since then are close in terms of. Yeah, it's uniquely large in its. in its, the degree of impact on biology. So again, I did want to emphasize that other large agonious events have caused major extinctions, just not as big as this one. Okay.

And so maybe it's just, you know, statistics, right? It's a statistical outlier. There's a range of these things. And this one happened to be a two sigma variation of the mean or something like that. It was the biggest. Yeah. It was the biggie. Okay.

But here, so volcanism occurred. huge increase in carbon dioxide and that caused many things and that's one of the other things you were well you studied in the library but you realize were were endemic were were characteristic of what was happened of what was seen in the extinction there and let's talk about those because the lesson of rising carbon dioxide is not just a change in temperature but it's many other things so why don't you talk about yeah no you're just right and this is something that uh really came home to me as we were thinking about this, that carbon dioxide can kill in several different ways. On the one hand, you put a lot of carbon dioxide rapidly into the atmosphere.

You get warming, and the planet warms, and that can have an effect on biology. When you put a lot of CO2 into the atmosphere, some of it goes into the oceans, causing the pH of the ocean to drop. something that's called ocean acidification. And that can particularly make life hard for organisms like corals that make skeletons of calcium carbonate. And then it turns out as seawater gets warmer, it can hold less oxygen than it can when it's cooler. So you should have an expansion, particularly in the subsurface of the ocean, of water bodies that have little or no oxygen in it. So all of these things happen. They're synergistic in the sense that each one makes the others worse.

And there's this wonderful physiologist in Germany named Hans Otto Portner. And Hans has actually talked about the deadly trio. And it's because these things are not independent of one another. They all happen at the same time. They all affect each other. And where we're leading, of course, is, you know, your listeners should at this point be saying, well, I've heard about all these things. And the answer is, yeah, because they're happening now. Well, in fact, that's why obviously

why I wanted to focus on it. But it's interesting to me because this permitting extinction, this release of large amounts of carbon dioxide didn't happen in decades back then or a century. It was more of, it was a longer term release, right? I mean, I assume this period of volcanism. rapid, it's more rapid than our ability to resolve time that I can account for. So it could have happened over thousands of years, but not millions. Thousands of years though, but the thing I want to get at is, is for the people who've made the obvious connection is we are doing the same thing, but not over thousands of years. And so the planet couldn't, one of the reasons people the extinction happened is that animals couldn't adapt quickly enough or

natural selection could adaptation couldn't happen on the time scale of this of this massive volcanism in rise in CO2 and that was maybe thousands of years we're now talking about a situation where we're releasing huge amounts of of carbon dioxide and i don't know actually that's a good question the comparison we've increased the carbon dioxide abundance in the atmosphere by 30 percent in the last century or so. How much do the carbon dioxide increase in the in the permune extinction? Again, this is all model dependent, but it might be dripling, something like that. And so, and we're headed on it, and we're headed to doubling it by 2050 or certainly by 2100. So we're headed towards something amazingly similar to the largest mass extinction we know of.

on a time scale that's even faster than it occurred naturally. Does this, what can we take from this? Well, a number of things. I think one is there is a difference between the end of the Permian and today in that our ecological crisis, which is building right now, is the result of human activities. and we can both, you know, understand the past and envision the future. And if we have a will to do so, we can do something about it.

So I think what people should take from this is something of a wake-up call. That, you know, it's not necessarily clear to me that we're headed for the loss of 90% of species in the oceans. But we are headed for a world that by the end of this century could be. fairly dramatically different than the one we live in now in terms of both physical environments and biological diversity and something we're already seeing, more extreme weather, larger development of wildfires, aridity causing water problems for people in many parts of of the world, sea level going up. You know, if you care to look,

you'll see that the world is changing at a rate that is faster than any of your ancestors could have imagined. Absolutely. And as I like to say, the basic science of it is not controversial, simple. I don't even know if you know, but my last book is called The Physics of Climate Change.

I'm in a short book on just the physics. And not the chemistry. Well, there are some chemistry of it. And so it is there, these are basic processes. There's nothing, these are well understood phenomena that have been understood for over 100 years and are the basis of much of modern physics and chemistry. But I think the point you made, which is really an important point, is that doesn't mean we're heading towards an extinction, especially for those people who think that it implies that

humans are going to become extinct. We are, as you say, a very different kind of animal. We can choose the, we can foresee the future, we can plan for the future, we can be stupid about it, or not. But I think it's really important to say that there are dramatic changes and many species will not survive those changes. The world will change, but it doesn't mean, it means we're going to live in a different world, but it doesn't mean we're not going to be living. I think that's a really important point. No, I think that's absolutely true. And in some ways, yes, we should absolutely be concerned about biological diversity.

But, you know, if you live in Florida, you should be very concerned about sea level change. If you live in Phoenix, you should be very concerned about growing aridity and worries about the water supply. If you live in Australia or California or many other places now, you should be worried about an increasing incidence of wildfires. And if you live in the eastern United States and Canada, you should be worried about an increase in extreme hurricane storms. So, you know, in addition to worrying about nature, there are reasons why we should be worried about the life. that most of us would like to live. Absolutely, and it's important, you know, I ended my book with the, with the phrase from Louis Pesture, Fortune favors the prepared mind. And I think that's one of the reasons why it's

so fascinating to learn and to talk to you and to learn about the, about how understanding the history of the earth prepares our minds, how the earth is a textbook if we choose to read it correctly, which you've done your whole life and, and, and, illuminated a lot for the rest of us in that regard. And, you know, I have to read the last paragraph of your book because especially it strikes me more now when you talked about, I asked you at the very beginning of this dialogue about your own interest. And it was a book on archaeology and you were kind of amazed that you were standing on this history. And I thought, wow, because that may be that, it really resonates with me when I read the last, I'm going to read the last paragraph.

So here you stand in the physical and biological legacy of four billion years. You walk where trilobites once skittered across an ancient seafloor, where dinosaurs lumbered across gingo-clad hillsides, where mammoths commanded a frigid plain. Once it was their world and now it's yours. The difference between you and the dinosaurs, of course, is that you can comprehend the past and envision the future. The world you inherited is not just yours.

It is your responsibility. What happens next is up to you. And so that lesson is important, but I like to think of the fact that archaeology, sure, you stood on the cultural history of humans and the fact that when you stand on the earth here, as you've now shown, we're standing on a, we're learning so much about the history of the earth that illuminates the present. And that would be a profound way to end this dialogue, but I'm not going to do it that way. I want to spend five minutes on, I know, I thought you were thinking, wow, isn't this poetic? And at least I was thinking that. But, but, but, but, I have to talk about Mars for a second because I know you've been involved in that. And I want to talk about, you know, especially since, you know, life on Earth here, we may, we may, we have an impact on it. And whether we end it through, through climate change or in some ways for many species or through nuclear war for our own, if we're, um, there, the universe has probably got life

elsewhere. And in fact, I remember, and you've been involved in Mars missions. And I remember you telling me, I'm sure you told me this. because again it was the first time i think i thought about this which is that um if we find you've been involved in the rover missions looking for life on mars extant or extinct likely extinct but but i think you said if we find life on mars you would be most surprised if it wasn't our cousins and um so so let me say let me let me let me i'm pretty sure i can attribute that to you and i don't I know I thought of that myself, but I think you were the first one to plant that seed.

And if I'm wrong, then forgive me. But anyway, comment on that statement. Well, yeah, I think I won't take credit for that. I mean, that implies that somehow life began either on Earth and was transported to Mars or and there's- Yeah, that's right. And there is certainly a school of opinion that has always liked the idea that life came to Earth from Mars, which simply kicks the can of origins down the screen. I've never, yeah. I think at this point, it's fair to say that we have no idea whether life ever evolved on Mars. We have now had through three rover missions that have looked at ancient rocks on Mars

in the same way that geologists look at rocks on Earth to reconstruct. our planet's history. And I think it's fair to say that one has not seen anything in those explorations that requires or perhaps even suggests the presence of life doesn't rule it out. And I think it's still worth looking for it as we try to understand the early history of Mars better. But as we are talking,

There's only one place in the universe where we actually know life exists and we're it. And we're awesome. And I certainly agree with you that statistically, if you think that life is, you know, really born of planetary processes and sustained by planetary processes, then, you know, just by the fact that there's, you know, billions of galaxies and each one has billions of stars and many of those that now looks have some sort of planetary systems. Almost all of it looks like. Yeah, that's right.

And so it really does, you know, it, in some ways it would be surprising if we were alone that the trick is going from that kind of statistical probability to actually demonstrating it. And that's hard. And that's hard. And you've got to find it. You can hypothesize it about, and most of, I think most of that, hypotheses, as I say, will be wrong because nature usually surprises us.

But what's, so what, if you're going to bet about Mars, what's the most exciting thing you've seen in the rover missions on the most exciting thing you'd like to see? Well, I think the most exciting thing, to be honest, was just the idea that I could actually do sedimentary geology and geochemistry on another planet and try to piece together the environmental history of another planet. You know, that's pretty much fun. That's exciting. Yeah, that's got to be amazing.

I do think one of the things, and again, this isn't without some loyal opposition, but with some colleagues, we published a paper recently in which we propose that while there's more evidence for wet Mars early in its history, that that wetness may have been episodic. So in terms of life, it makes a, it's really different if you have, you know, a sort of temperate wet planet for 300 million years is different from having a temperate wet conditions for 100,000 years every 20 million years. Yeah, yeah. We at least think the latter might be closer to the mark.

But again, those are hypotheses that can be tested through continuing research. Okay. Two, two other related questions, I guess. One is, is it not true, though, getting back to my cousin question, that if life developed on one or the other planet, which we know developed on Earth, it would be hard not to put, if the conditions were compatible in some ways, it would be hard not to pollute the other planet with life. Well, we do know, certainly we have meteorites that come from Mars.

Yeah. And we've identified with certainty. I think things would go in the other direction, although I think that the trip from Mars to Earth is more probable. I think the biggest impediment to that is, let's say you have some specific environment on Mars that has some kind of microbes in it that are adapted to that environment. And you take it and randomly drop it onto an early Earth, what are the chances that it would land at a place where those bugs could thrive? Again, you can't say it couldn't happen, but it's probably not a really high probability. So again, you know, I don't tend to spend a lot of time thinking about things that I can't do anything about, but I think I tend to think of Earth and Mars in terms of their own merits. and if someone, you know, at some, you know, it's a moot point until someone,

and unless someone provides evidence that there was ever life on Mars. If that's shown, then we'll have some interesting conversation. Yeah, yeah, yeah, right now it's, it's, but you're dubious. But let me, let me then, the second last question. What about where, well, let me, where do you think the most likely place, if we're going to find life in our solar system is, Europa and Solitas, do you think those are more likely environments or just throw it out. Oh, you know, I think Mars might be the best place.

Certainly Europa and Enceles are interesting in that, you know, they do seem to have liquid water beneath a surface and organic material. And you could get, you know, probably a limited biomass in those environments, but it's not impossible. So I am a great fan of actually, you know, using some of NASA's resources to explore those moons in more detail. Yeah, no, I mean, I think it's fascinating the idea because, first of all, we do see those guys you're spewing out some of those moons and they have salts, organic materials and such. And it would be fascinating. And the other thing that's nice about it is that those are systems that have definitely been cut off by the ice.

So, I mean, if you found life there, you'd know it was an independent genesis. It would be definitely an independent genesis of life. Speaking of Mars, you know, one of the things I've always, I love the rovers. I'm a huge fan of the rovers. And for me, I feel like I'm on Mars just as much with a rover as I would with an astronaut. So I never understood this fascination of sending people up there. But do you, and I've always said you can send, you know, a rover to Mars for the price of making a movie about sending a human to Mars. and and so cost effective is one.

I have friends of mine who are geologists who say the opposite, they'd like to put a geologist on Mars, but what's your view of given the resources of the rovers versus human space exploration? Well, I think you put your finger on a very important thing, and that is the cost of putting a human there with anything approaching safety is hugely high. you don't get much change for your trillion dollars when you do that. So I think that that if the United States and its partners are to do something like that, it is something I think that requires a conversation because the trillion dollars you spend on that is not something you'll spend on other things.

Eating the hungry and that sort of thing. And you're right. I think that just the increases over the last. last 20 years in rover capability suggests to me that we can have very, very capable science done by, you know, smart rovers in the future. So I suspect if the decision is made to go to Mars, it will be more out of a sense of manifest destiny than it will the scientific requirement of sending people up there. So we will see. I will probably be safe. in my grave by the time that happens. So I'm glad to see, yeah, yeah. I mean, most, I'm glad to see you throughout the trillion dollar number because

people seem to think it's just easy and it isn't. And, uh, and the other thing, and you the point, the key point on the head that that rovers technologies, you know, technology in Earth is improving so fast. And you may say, well, you know, a geologist could do in a day with the rovers during year, but a thousand rovers could do, you know, as much as, or more than a geologist could do by being in a thousand Yeah, and we've actually suggested this to JPL that it would not be very expensive to have a sort of a fleet of kind of mer capable rovers. You know, you could have instruments that switch in and out for various places, but really explore the planet. In some ways, it's mind-boggling what we have learned about Mars, but we've only, you know, had boots on the ground, if you will, a handful of places.

And so there's a great deal left to go. And if nothing else, I think we have a lot to learn about, you know, if we were to send a person or people to Mars for scientific purposes, what is so important that you would send them to a particular place? And I think we're still fairly ignorant about those details. Yeah, yeah. Oh, absolutely. And you hit the other point is that we don't, we, as far as I can see,

have never sent humans into space for scientific reasons. It's always other reasons. Because if it was for, because when you think about scientific reasons, there's no reason to send humans into space. If you're a bottom line, it's adventure and other things in politics. Last question, quickly, what's the most exciting thing in the future? History of life on Earth, Mars, whatever. What are you looking forward to next? In terms of science or in terms of the actual future? Let's just stick to science for the moment. Good. There I have stronger opinions. I think that, you know, if I look at my own home territory about trying to understand the history of Earth and life, you know, in the last 10 or 15 years, we've come a long way in trying to integrate records.

And so we have now a reasonably good first order understanding of what happened. And more and more work is going in to try and understanding why certain things happen. You know, we know that the great oxidation event happened. But why did it happen? You know, we know that there's more oxygen coming in at the end of the Precambrian. We know that there are these snowball glacations. Why did they happen? And I already see, you know, particularly through the work of some bright younger colleagues that, you know,

new types of models, new types of integration of different types of data is taking us in new directions. So if I were to, you know, just pick one thing about the future of natural science, it's the integrative nature of science as we move forward. Sure, the fact that 19th century disciplines were 19th century disciplines and not 21st century, which is great. Well, look, this has been fascinating and enjoyable and I can say with great honesty that it's wonderful to be with someone who's not just a scholar but a gentleman. And thank you very much, Andy, for taking the time. Thank you. And congratulations once again on the prize. You take care. I hope you enjoyed today's conversation. This podcast is produced by the Origins Project Foundation,

a non-profit organization whose goal is to enrich your perspective of your place in the by providing access to the people who are driving the future of society in the 21st century and to the ideas that are changing our understanding of ourselves and our world. To learn more, please visit Originsproject Foundation.org