Reading Planets through Rocks: A Conversation with Andrew Knoll

Jennifer Berglund  

Welcome to HMSC Connects!, where we go behind the scenes of four Harvard museums to explore the connections between us, our big, beautiful world, and even what lies beyond. My name is Jennifer Berglund, part of the exhibits team here at the Harvard Museums of Science and Culture, and I'll be your host!


Jennifer Berglund  

Today, I'm speaking with Andy Knoll, a now emeritus professor of earth sciences and biology, with dual appointments in the Department of Organismic and Evolutionary Biology, and the Department of Earth and Planetary Sciences at Harvard. He's interested in how physical and biological processes have interacted across the span of our planet's history to shape our world. I was curious to learn more about how he reads Earth's history through rocks, and how what he has learned informs our understanding of our current plight on Earth today. Here he is.

 
Jennifer Berglund  

Andy Knoll, welcome to the show. 

 
Andy Knoll  

Thank you, glad to be here.

 
Jennifer Berglund  

Your journey to becoming a scientist was somewhat indirect, but may have begun during a fifth grade trip to collect fossils. So, tell me that story and how do you think it may have set you on your path?

 
Andy Knoll  

When I was in the fifth grade, my brother was in the eighth grade and his science class had a field trip. And my father was commandeered to be a driver. And so then I was corralled into going along. The field trip was to look at what I now know, our Devonian sedimentary rocks ,not far from our home, that contained fossils. And while I don't think my brother was especially excited by that trip, I just thought it was amazing, I would take a piece of rock, split it with a hammer, and I would see something that had been alive millions of years ago, and that no human being had ever seen until I split that rock. Now, in all honesty, given my sort of rural background,

 
Jennifer Berglund  

You're from rural Pennsylvania, right? 

 
Andy Knoll  

That's right, I really didn't know that there was necessarily a profession that would allow me to work with fossils. But it did excite in me this sense that there was this history of life just in the rocks waiting for you to unravel it. And you know, in the fullness of time, that's where I ended up. 

 
Jennifer Berglund  

At that age, it's not like you really decided right then in there that you wanted to go into the sciences, it was more kind of a gradual thing. And when you were young, you really just decided that you wanted to find some way to travel the world. 

 
Andy Knoll  

Yeah, that's exactly right. And that has worked out better than I ever could have anticipated, since a lot of my research over the years has involved fieldwork into places that one would never see unless you were doing geologic fieldwork. And also, you know, science is a very international endeavor. So through meetings and visits to laboratories, in that I've had tremendous opportunities to work with people from many different cultures.

 
Jennifer Berglund  

Eventually, you found yourself in college, and ultimately in grad school, but you maintained throughout your advanced education and interest in biology and earth sciences. Tell me the story about how those two intersected for you, and led to your globe trotting career studying the early evolution of life.

 
Andy Knoll  

It's fair to say that when I was 18 years old, I hadn't the slightest idea of what I wanted to do or should do in life. And again, the professions that I knew something about were doctors, lawyers, and engineers. I knew I didn't want to be a doctor or a lawyer. And I was pretty good at math. So I went to engineering school. And then by the end of my freshman year, I also knew I didn't want to be an engineer. So the first semester of my sophomore year, I simply took six math and science courses, hoping that something would rub off. And actually two things did. I took both a biology course that I really found fascinating and an Earth science course, that I really enjoyed. And sitting in my room one night, it dawned on me that maybe these were not the separate universes as they seem to be from the way they were taught in those days. That maybe from some perspectives, they ought to be seen as two sides of the same coin. And then I remembered that paleontology was one area where earth and life come together in very important ways. And that's really what set me off in general on this journey to try and understand how Earth and life interact through time. If you look at the environmental history of our planet, for the first billion years or more of life's history, there was no oxygen in the atmosphere or oceans. I mean, you and I, if we were transplanted to the world 3 billion years ago, would have lasted a few minutes at most. Then, about 2.4 billion years ago, through an interaction between evolutionary innovations, which was the evolution of photosynthesis that uses water as a source of electrons that gives off oxygen gas as a byproduct. And actually tectonic, or physical changes, that greatly changed the landscape as far as primary production was concerned, the earth just underwent a fundamental change, and it didn't become modern. But it became a world in which at least single cells that use oxygen could thrive. And then another billion and a half years later, there's a second oxygen revolution, again, with the interaction of photosynthetic organisms and tectonics, that essentially gave us an atmosphere and oceans that could support large animals. So that whole history of oxygen, which is the fundamental rate keeper of evolution, in very profound ways, reflects the interactions of physical and biological processes. 

 
Jennifer Berglund  

This is interesting, because we just redid some of our cases in our mineral Hall in the Museum of Natural History. And one of our new cases talks a little bit about mineral evolution. We divided it up into three stages, where you have the early stages of mineral formation as the Earth was forming. And then as you were talking about, you have those minerals interacting with each other, essentially, and with water on the earth, and different materials that way. And then, as you were saying, this third stages, the minerals interacting with life. So this is actually a very important point for the study of mineral evolution. So what you were tapping into as a college student in those days is actually, in fact, very important to the entire field.

 
Andy Knoll  

It works both ways. Not only do organisms influence the environment, which in a way dictates what minerals can form. But also, as most people who are listening to this will recognize, many different kinds of organisms actually precipitate minerals. Today, nearly all of the limestone formed in the oceans begins as skeletons. And so it's another interaction between the biology of marine organisms, and what most people would consider a physical process, the formation of limestones on the seafloor.

 
Jennifer Berglund  

You've described, every rock is having a story and every cliffside as its own library, which is just a beautiful way of thinking about it. But can you describe what you mean by that, and how that plays into your work?

 
Andy Knoll  

In many ways, the history of our planet is written in sedimentary rocks that are laid down one bed at top another through time. And you know, if you go around today and look at modern environments, you'll see that sediments are accumulating different places - sands are forming in one place, muds in another limestones in a third. And if you look at the physical characteristics of those beds, as they accumulate, they carry clues to the physical environment of sedimentation. And then if you get serious about them and look at the chemical makeup of those rocks, they carry clues to the chemical environment when those rocks formed. So basically, every rock has a story in its physical, chemical, and in many cases, biological components. And the whole training of a field geologist is to try and read those the way a medieval scholar might want to read old English. One of the things that I did early on in my career was to establish a research program on the Arctic island of Spitsbergen, which is pretty much halfway between the northern tip of Norway and the North Pole. And there was a particular rock there, which geologists would call a flake conglomerate. And what that really means is that it consists of little flake like pieces of sediment that had originally formed as microbially built layers, and then was basically ripped up by storm and re-deposited in a lagoon and that whole story is something you can deduce from the physical characteristics of the rock and why this particular rock is important to me is that many of those flake like particles were actually transformed by silica SiO2, quartz if you will, soon after they were deposited. And they preserve a remarkable record of the organisms that lived along that tidal flat 800 million years ago. So there are two things going on. One is that you actually have preservation of fossils, but equally important, the physical features of the specimens tell us where the organisms that formed the fossils lived in life. 

 
Jennifer Berglund  

I'm glad you brought up Spitsbergen because this is actually a really important place the beginnings of your career. Tell me about that first trip traveling there, what were you doing? Who are you traveling with? How did it shape you as a scientist? 

 
Andy Knoll  

The story begins really when I was a graduate student, and I spent a lot of time in the library, just reading the geological literature on ancient rocks, just so I'd have a better sense of what the opportunities might be. And as I started my own career as an assistant professor at Oberlin College, I decided that this place called Spitzbergen, really seemed very promising. So I actually wrote, since there was no internet at the time, a man named Brian Harland at the University of Cambridge in England. Brian and his students had done most of the work on the rocks I was interested in and Brian, bless his soul, simply said, I've been hoping somebody be interested in this, why don't you just join us this summer. So I spent two months in 29 foot converted Norwegian fishing boat, with three other people basically sailing around the northern tip of Spitsbergen, around 80 degrees north latitude, and sampling the rocks. And it turns out that my intuition was right, these rocks turned out to be extremely fertile in terms of fossils. And as we eventually started looking more closely at their chemistry, they really changed the way I thought about the environmental evolution of the Earth as well. So Spitsbergen was really were the ways that I've come to work on and think about the rock record were hammered out. In science, almost every discovery leads to more questions. And so in some ways, the one of the most important things you can do as a scientist is to articulate good questions. And as I did that, I started thinking, well, where would I go to do this sort of thing. So I spent a good decade working in various parts of the Arctic, mostly on rocks that were between about 600 and 900 million years old. And then I had this remarkable opportunity to work in northern Siberia. And I spent six months of my life over three field seasons, working there, mostly in rocks that were a little bit older. And so that took this whole integrated view of Earth and life backward in time. And I guess the short answer to your question is that as you learn new things that prompts new questions, and then if you know enough about the geology of the world, as 100 years of geologists have described it, that really helps you to say, this is the thing I want to do next, this is the issue I want to tackle next.

 
Jennifer Berglund  

One really interesting thing about your work, you're essentially looking at microscopic fossils, correct? Do you have to be able to read the rocks in a particular kind of way where you know that there is some sort of microbial life imprinted in them that you can't necessarily see with your naked eye? 

 
Andy Knoll  

When we think of life, I think in general, people think about plants and animals. But there's probably 30 tons of bacteria on earth today for every ton of animals. And for most of Earth's history, there were no animals. So for the first 85% or so of the history of life, life was largely microbial. And so if you want to understand that long history, you have to look for clues that microbes can leave. And so what people have found out, and this is not uniquely me, but a number of us who worked on these rocks of this age found that certain types of rocks give you a relatively high probability of discovering fossils. And so we made sure that we collected these very systematically as we worked our way through sections. But the other thing that we did, that has really paid dividends, is that we just collected everything systematically. So if there's 1000 meters of rocks of this age, we collected at least one sample every meter. And it turns out that some rocks that don't contain microfossils actually contain really informative chemical clues to the history of life and environments.
 
Jennifer Berglund  

And that's how you're reading cues about the environment in which these organisms lived?

 
Andy Knoll  

Yeah, if you look today, organisms that you find on a tidal flat are not the same organisms you find in a river basin, and they're not the same organisms you find in a coral reef. So it's pretty clear that, today, the distribution of life on our planet, is to a first approximation, governed by environment. When I first came in to working on the early history of life, people were interested in how things changed through time, but they hadn't done the work of seeing how life at any one time was distributed among environments. And so that's one of the contributions that we made. And I think that has helped us to really get a much more nuanced sense of the extent to which evolution versus ecology shaped the record that we're seeing. 

 
Jennifer Berglund  

This is also very interesting because your work has actually taken you off of the planet, you've also worked on a Mars mission. So tell me about that work, and how you've used your previous work on Earth to understand Mars, and in turn, how understanding Mars has enhanced our understanding of our own planet.

 
Andy Knoll  

This is a story that actually begins really in 1996, when a famous or infamous depending on your point of view, paper was published in which a group of scientists claimed to have found evidence of life in meteorites that originated on Mars. And you know, the controversial part of it was not where did the meteorites originate. They were certainly pieces of Mars that had been essentially blown off by meteor impacts and ended up on the Earth. But the evidence was quite controversial. 

 
Jennifer Berglund  

I have a question about that. How do we know for sure that they came from Mars?

 
Andy Knoll  

It turns out that there are at least two types of chemical clues. In some Martian meteorites, there are actually little bubbles that preserve evidence of the Martian atmosphere at the time they formed, and that is quite distinct from the atmosphere of the Earth, we know much less about things from the asteroid belt, but there was a close match between the composition of the air trapped in these bubbles and what we know about the Martian atmosphere from NASA and its international partners research. Also, if you look at a chemical detail, which is the so called isotopic composition of oxygen, and what that means in plain English is that oxygen atoms have eight protons and eight electrons, but the number of neutrons can actually vary. It can be eight, nine or ten. And so you have these different weights, if you will, of oxygen. And those are extremely valuable in earth science. And, since the oxygen isotopic composition of Martian materials is distinctly different from that of Earth, once again, it became very clear that some of these meteorites very likely originated on Mars. 

 
Jennifer Berglund  

But it's not like a meteorite hunter's walking around looking for meteorites, and they spot something and they're like, "Oh, this is from Mars. This is definitely from Mars." How are they discovered? How do you know to even look at the isotopic composition? 

 
Andy Knoll  

Well, people have been collecting and analyzing meteorites for a long time. And that originated in sort of serendipitous ways, including people actually seeing meteorite falls and collecting the debris. But, this is probably about 40 years ago now, people started to recognize that you could get a lot of help and collecting meteorites if you let Earth do a lot of collecting for you. So people started working in Antarctica, where through time, meteorites would fall on the ice, and be carried by the ice to the edge of the glaciers and then deposited there. So that dramatically increased the number of meteorites that scientists had to work with. And people started recognizing that there were differences among them, not all meteorites are the same. And in order to unlock those differences, you had to do careful work on the metrology that is the microscopic features of these items and on their chemistry and through time, that gave us this much, much better sense of both the variety of meteorites, what they're trying to tell us about the formation and early history of the solar system. And, there's now, I'm not sure what the number is, but it certainly several dozen or more meteorites, whose distinctive composition tells us that they originated on Mars.


Jennifer Berglund  

You were telling me about this infamous paper that came out declaring that there was evidence of life on Mars and these meteorites? 

 
Andy Knoll  

Yeah, that's exactly right. And it's fair to say, I was actually at a meeting, the day that paper came out and all anyone talked about at breakfast, the next morning was this paper, and not very much was positive about it. But NASA noticed something. And that was that people were interested in it, the public was interested in the question of, could there be life somewhere else in the solar system? So I think it was actually Al Gore convened a meeting in Washington and invited a couple dozen scientists of different types to come and consider the question of how NASA might alter its solar system research program to really put the search for life on the front burner. And I was invited to that. And there I met a then young planetary scientist from Cornell named Steve Squires. And Steve was actually in the process of putting together a proposal for a Mars mission. And Steve recognized that in addition to people who build and operate instruments, and those people are just wonderful, we couldn't do without them, it might actually be helpful to have a couple people on the team who had experience actually interrogating and interpreting ancient rocks. So Steve basically said, "How'd you like to be on a Mars mission?" And then I said, yeah, sure, why not not knowing that this would take over my life for a decade or more. And it really worked out very well. I worked mostly on famous rover called Opportunity. And the first images that Opportunity sent back to Earth when it landed, showed that it had landed within a few meters of outcrops of sedimentary rocks. And so we just then treated those rocks basically the same way you treat rocks from Earth. You try to understand their physical features using the instruments on board the rover, understand their chemical features. And that, through a lot of work on a series of missions now, have allowed us to go a long way toward reconstructing the environmental history of another planet in much the same way we have reconstructed the environmental history of Earth. 

 
Jennifer Berglund  

And by the way, the presence of sedimentary rock means that there was water. 

 
Andy Knoll  

Well, it doesn't necessarily. I mean, you can get rocks or sediments that are formed by wind blowing particles and that. But in fact, every mission that has looked at ancient sedimentary rocks from Mars has shown that at least episodically, there was substantial water on early Mars. One of the questions has been, was Mars continuously wet and temperate for hundreds of millions of years? Or, and this is where I land was Mars repeatedly, warm and wet for short intervals of time, separated by intervals of varying length where it was cold and dry? That's still something that is debated. But we now have a level of information to actually conduct that debate and construct the models to understand what we're seeing that I think would have been impossible even 25 years ago. 

 
Jennifer Berglund  

And when you say short intervals, what are we talking about? 

 
Andy Knoll  

I mean, there's evidence from lakes and river systems on ancient Mars that there must have been liquid water for thousands, perhaps tens of thousands of years. But you know, when you add up all the evidence you have for standing water or flowing water, make estimates of how much time would be represented by that, and then make the crazy estimate that all of these are different ages, which probably isn't true, you've only accounted for a couple of percent of the time interval involved. So it may well be. And again, I say this is not canonical knowledge. This is, I think, the way at least some of us would piece together the puzzle as it appears to us right now that because of volcanism or large meteor impacts, you might have had warm wet conditions for tens of thousands of years, but then have dry terrible for life conditions for the next million. 

 
Jennifer Berglund  

What do you think the chances are of us finding life on Mars? Or past life on Mars? 

 
Andy Knoll  

I think the chances of finding present day life on Mars are very, very small. There's a wonderful series of novels by Kim Stanley Robinson called Red, Blue, and Green Mars. And in the preface to the first novel, he just says, we are the only intelligence Mars has ever known. And I think that's a good place to start. But we may be the only life at all that Mars has ever known. To date, we have no direct evidence for early life on Mars. But it's not impossible that you could have had even repeated origins of life that persisted for short intervals of time. And by the continued systematic mapping of Mars as missions are available, I think it's important at least to keep that search in mind.

 
Jennifer Berglund  

Do you think it's possible for there to ever be a human settlement on Mars? Since we're talking about it, I have to ask.

 
Andy Knoll  

Well, I certainly know people who would volunteer, even if they knew they were never coming back. It's an interesting question of what would be the point and the benefit of that. I think a lot of the people who are excited about a potential human presence on Mars see it as sort of a manifest destiny, that, you know, we have the tools, and we should have the ambition to colonize the solar system. Set against that is a question of, if I started today to plan a human expedition to Mars, it would probably be 20 years before it could happen just because of all the planning you need to do. And, you know, 20 years from now robotic missions to Mars will be really sophisticated. So there's the question of, is there actually a scientific rationale for going to Mars? And, you know, this is not a kind of mission from which you're gonna get a lot of change from your trillion dollar bill. So I think that, should NASA or any of the other important players in solar system exploration, before committing to that, I just think it's something that should be open to public debate. Do really want to devote that money to having someone set foot on Mars? Or would you rather cure cancer or things like that? And again, I don't want to bias the debate, I think there are arguments for that kind of exploration. But given the costs of that commitment, I don't think it's a decision anyone would make lightly.

 
Jennifer Berglund  

I want to come back to Earth from Mars, and talk a little bit about how studying other planets like Mars informs our understanding of our own planet. Can you talk a little bit about that?

 
Andy Knoll  

One of the things that we've learned through the work of many, many people is that the expectation is that stars in the universe will have planets. Many, many solar systems, 1000s of planets have been found, which are orbiting around stars other than our own. So in a sense, one of the questions one might ask is, you know, is the earth in any way representative of this galaxy of planets. And even to get any sort of sense of that we need to start comparing Earth to what we see on other planets in our own solar system, and what we're starting to learn about planets surrounding other stars. And in many ways, I'm more taken by the differences between Earth and at least those other planets that we can characterize. So for example, one thing that makes Earth different, as far as we know, from Venus, and Mars and other planets and moons in our solar system, is that we have this internal dynamism of the planet called plate tectonics. Plate tectonics is not something that has to occur on a planet. And there's a lot of debate about when it actually started on Earth, and under what circumstances. But plate tectonics may actually fit back into this whole question about life. It may be that what makes Earth unique, at least within our solar system, is not that it was the only planet ever to give rise to life. But that life has persisted despite all odds for 4 billion years. And plate tectonics plays a role in that. So, in some ways, if nothing else, learning more about other planets, makes us appreciate what is distinctive and special about our own planet.

 
Jennifer Berglund  

You retired during the pandemic, but you still hang around Harvard is an emeritus professor. And one of the things that you've been up to is you wrote a book. It's called "A Brief history of Earth: Four Billion Years in Eight Chapters" Tell me about that book. What's the concept? How did it come about? I must say I've been reading it and thoroughly enjoying it.

 
Andy Knoll  

Well, thank you. I've always liked writing. In fact, when I was in high school, I probably would have told you that I wanted to be an English major and not a science major. And, you know, I think communication is so important in science. So that I have stressed in my own work and in that of my students that, you know, if you can't communicate, you're in trouble. And so one of the things that pending retirement did was free up time for doing more writing, and particularly of types that I had not done before. So I had actually thought about writing something for a general audience. And just by sheer coincidence, and good luck, I got a phone call out of the blue by an editor from HarperCollins, who said, you know, I think we need a good, short, informative book about our planet. And I think you should write it. You know, after that conversation, I went home, and I talked to my wife, and I decided, well, yeah, maybe, maybe I should try that. And so the intent of the book, which is twofold, is one, just to give an accessible sense of how everything around us came to be; the mountains, the valleys, the oceans, the biology, because you know, that's actually what Victorian British would have called a ripping yarn. It's a fascinating story. And by having some sense of that story, you just have a whole new appreciation when you go to the Alps, or the Rocky Mountains, or the Grand Canyon, or even just go down to the beach. And at the same time, one of the things that has concerned me most about 21st Century global change, and the public's reaction to it has been the indifference of many people, perhaps most especially in the United States of America. And it struck me that maybe if people understood how we got here in the first place, and if I could then place 21st century change in the context of Earth's deeper history, it might help people to understand the gravity of our situation in the 21st century. 

 
Jennifer Berglund  

Well, I highly recommend the book to anyone out there listening. It's really fabulous. And Andy, you're just such a beautiful writer. Another thing that you've been up to in your retirement is you received a pretty amazing award. Recently, it's the 2022 Crawford Prize in Geosciences by the Royal Swedish Academy of Sciences. And it's essentially a compliment to the Nobel Prize. And you received the award for fundamental contributions to our understanding of the first 3 billion years of life on Earth, and life's interactions with the physical environment through time. That's a really big deal. Tell me a little bit more about the work that earns you this really important award.

 
Andy Knoll  

The only the first thing to say is that, I don't know any scientist who gets up in the morning with the ambition of winning an award. Science is hard. And I think you only succeed in science if you get up just wanting to know how the world works. And so that's what's driven mej just curiosity through time. And the thing that I'm grateful for with this award is that you know, it basically saying you've done good. That over years of doing fieldwork and laboratory work and paleontology and chemistry, working on other planets that the Swedish Academy felt that these were useful contributions. And it still seems a little surreal, but I'm grateful for it.

 
Jennifer Berglund  

What would you identify as your most significant contribution?

 
Andy Knoll  

Well, I guess there's two answers to that. I mean, the canonical answer is I think that my students and I have done a disproportional amount of the paleontological work that has given us our sense of the early history of eukaryotic cells, that is cells that have membrane bounded nuclei, like our own. And so that's, I think, a useful contribution. At the same time, years ago, I came up with a, at the time very far out proposal for why Earth lost 90% of its species 252 million years ago, one of the greatest of all mass extinctions. And it turns out that we were right, that it was a massive, rapid increase in carbon dioxide. And that's important because all the things that seem to have affected life during that catastrophic event, are things you can read about in the paper right now, because they're happening in the 21st century. And then the other thing, and this is going to make me sound like a boy scout, which I wasBoy Scout, kid. But one of the things I really the most proud of is that I've been able to work with 40 graduate students and postdocs and a number of undergraduates. I was very pleased to see a list of what someone opined were the top 10 universities in the world and was pleased to find that I had 11 former students and postdocs on the faculties of those universities. So, you know, at the end of the day, just the chance to help wonderful young scientists find their own way has been, to me, certainly as satisfying as any of the scientific contributions. 

 
Jennifer Berglund  

Well, this kind of leads into my next question for you. Because reflecting on your long and storied career as it has been, what do you feel is your greatest accomplishment? Is it working with students and sending them on their way?

 
Andy Knoll  

Yeah, I think it really is. You know, it's not that I'm unhappy with the research contributions. And a lot of the work was done by students who are working in the lab. So it's not like I was sitting by myself and doing all of this and seeing there's something special about seeing those who you have maybe helped a little bit along the way doing well. And that's another thing that gets you up in the morning.

 
Jennifer Berglund  

Yeah, it's like rearing graduate students and postdocs is much like rearing a child in that way, you know. 

 
Andy Knoll  

Broadly speaking, 

 
Jennifer Berglund  

Broadly speaking, yes. But helping them grow intellectually, and then sending them off on their own for success.

 
Jennifer Berglund  

What do you hopenyour work inspires in others?

 
Andy Knoll  

I think two things, and this goes back to the rationale for writing the book we were just discussing. What I would really love is if, not only in our own country, but throughout the world, there was a greater appreciation of what is really a tremendous legacy that we have inherited from 4 billion years of planetary evolution. And that, with that, there would come a greater commitment to preserving that legacy for our grandchildren and beyond.

 
Jennifer Berglund  

Andy Knoll, thank you so much for being here. This has been absolutely wonderful. 

 
Andy Knoll  

My pleasure. 

 
Jennifer Berglund  

Today's HMSC connects podcast was edited by Emma Knudsen and produced by me, Jennifer Berglund, and the Harvard Museums of Science and Culture. Special thanks to the Department of Organismic and Evolutionary Biology, and the Department of Earth and Planetary Sciences, and to Andy Knoll for his wisdom and expertise. Thank you so much for listening. If you'd like today's podcast, please subscribe on Apple Podcasts, Spotify, Pod Bean or wherever you get your podcasts. See in a couple of weeks!