Andy Knoll: The First Four Billion Years of Life on Earth

[Music] hi i'm lawrence krauss 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 was a spectrum of radiation coming from through that star and you're 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 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 them 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 noel of harvard university andy is a it's hard to define him he's a geo a geo biologist 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 suggest that the rise of sudden rise of carbon dioxide was perhaps responsible for the last major extinction on earth a very topical subject uh 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 in 2018 and just this year was awarded the crawford prize of the royal swedish 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've learned a tremendous amount from andy over the years i've actually he tutored me early on on on many aspects of the development of life when i wrote my book adam and we became friends then and i've enjoyed his writing ever since he's written some very cogent books on on the first few billion years of life on 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 watch the discussion on our sub stack 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 if you if and in that case i hope you'll at least subscribe to the channel to get more information on upcoming events and uh 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 and renault as i was [Music] 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 after a while i haven't seen you so thanks for being on the program and and uh and i'm sure it'll be enlightening um and i love the background behind you which is not real but but uh my background is real but yours uh i don't think you're you're doing this remotely but yeah that background will be probably relevant to some of the things we're going to talk about i think and uh yeah and uh i i want to say in advance that um you have been my teacher for many many years and so many years ago when i uh when i was writing my book on on adam um 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 uh i i benefited tremendously from your wisdom and experience and um and i'm really happy to to do that again and to give other people an opportunity to do that in the in the context of uh uh your new newest book with a brief history of life on earth which i want to use as kind of a guide uh 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 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 i i i guess i realize how important it is uh because i wasn't the first person to realize how important it was most recently i want to congratulate you on the 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 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 uh it was 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 but of course i i want to learn more about um what one thing i don't know i know we you and i have talked about about the evolution of your time a little bit from 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 probably doesn't differentiate me from most 18 no but well it's that's a i like to say that's a great thing i'd be sad if when if you're 18 you knew what you wanted to do i mean for some people that worked 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 be a doctor or a lawyer so i went to engineering school and then being really a bright uh teenager i realized after a year that i didn't want to be an engineer either 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 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 on you know proceeded from well you know that's an amazing realization and i will say and 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 and well that that probably gives me too much credit to be honest um 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 in the wilderness that i think the 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 it 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 is 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 um you know at the wrong time it can be a waste i i think i've said before in this program i remember when i was doing my phd uh at mit down the road from where you were at harvard but a little bit later um i i got discouraged in particle physics and i thought of going into into biophysics and um and i was gonna do a joint phd md at harvard mit and and then and some 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 seven late 70s and he said because biophysics isn't of interest to biologists and it isn't of interest to physicists and and he may have been right at the time but of course 20 years a decade later yeah exactly a decade later it was it was exactly wrong but uh 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 i wonder about i i have a friend of mine who's a became a physicist and um um and he wrote a poem i think in kindergarten when i when i grow up i want to be a doctor of philosophy and i was amazed because i would never have known uh is now a professor in in in british columbia um he and he did his 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 uh so i'm wondering about your parents what what uh what their background was well um you know my parents grew up during the depression you've had uh uh you know understandably an important influence on their lives and and my dad basically went from a depression at depression era high school into world war ii so he didn't have time to to go to college and when he got out you know he wanted to settle down and uh became a bank teller and blah blah blah my mother whose uh father came from germany and was more yeah i think education was more central in his view of the world he was an engineer she did go to college and and became a teacher so my parents um you know they were good hard working people they they always supported me i think when i told them that i was going to become a geologist and paleontologist 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 maybe he'll be okay good okay that's you know that's good that she didn't continue working 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 say 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 um what was she went to college and studied what uh basically education home economics and then you know she became a teacher uh after okay did you read so 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 um um i you know 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 schliemann 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 lawrence i i rarely got up in the morning and thought hmm what should i do for yeah sure my life i was more worried about you know what i was going to do on saturday night that's a 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 and you know being at harvard and living in sort of an academic community i've always been amazed uh when i taught new haven uh the people parents are worried what their kids how well they're writing in kindergarten or whatever it is i mean they're worried about getting what college they're going to get into and it's it's kind of sad that kids are so pro 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 uh but that's good okay so you um um 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 well music has always been important avocationally i actually met my wife uh 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 women's school and so we got together to sing choral music um you know in both in graduate school we both sang in the chorus pro musica a very very good chorus in boston uh at what i taught at oberlin for five years we were in the oberlin community chamber singers and 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 a good high school teacher of music and which i have great the greatest respect on earth for people who do that and succeed in it but i 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 uh um donald glaser who was uh who was one of pete won the nobel prize in physics and he was at berkeley and he was um and he was interested in music he played the violin i think and he and he was also sort of interested in science my dog and cat are fighting here i'm gonna i'm gonna have to just wait one second i'll be right back and remove them okay okay guys anyway there we go they just i knew they were gonna at some point decide they didn't want to hang around here okay but anyway let me repeat this uh so donald glazer um won the nobel prize in physics uh uh for discovering a new way to detect elementary particles actually and uh but he told me a story he was a violinist a pretty good one in in in cleveland um which has a great orchestra might and and i know oberlin's music because 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 it's so he went into science because he figured even more have changed but he's right uh 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 have to be exceptionally talented you have to be exceptional that kind of career yeah it's amazing i'm because of my daughter who's very musical i got involved you know got to see that firsthand in cleveland with the cleveland orchestra and uh and uh it was really kind of amazing to see and and going to aspen where there's a physics institute but also a music school to see the the wrongs 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 weren't going to be employed so that yeah you all was lucky you chose that then and uh and ended up okay as a scientist but okay so you you as an undergraduate um and and and you were let's see your phd at harvard you did your undergraduate degree where again i forget lehigh university pennsylvania in pennsylvania where you'd grown up in pennsylvania okay but uh and i remember talking to you about this when we first met um you you chose to 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 do it to went in to teach at oberlin right after that and um 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 for a uh a letter of recommendation and i wrote it and i didn't know what he was what 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 he be that was a huge experiment and he moved back from overland to to become a researcher at nasa and then and then moved to become a professor but why did you choose um 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 and which is in 1977 um it was not the standard practice in earth sciences to do a postdoc oh i didn't know it is now but some people did it but many people went right into a profession and and to be honest at the time i thought a place like oberlin was was just ideal there's all the music and and b you know i i saw a lot of things that i didn't particularly like about the research environment at harvard in the 70s and so uh you know i i wasn't fleeing from it but i realized i didn't have to to do that and i might be happier if i didn't um 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 my research trajectory and then it turned out i you know fortunately i had good luck in research and realized that there were at oberlin or or any other liberal arts college although they support research there are walls to what you can do and and then um harvard came around and said well you know we have uh an opening why don't you apply for it and since it was actually in the town where my wife had uh an elderly father yeah and and you know 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're at oberlin you did your first set of groundbreaking research if i'm if i'm not incorrect is that true yeah um things worked out well i i started doing field work in spitsbergen which turned out to be this wonderful geological library for uh a portion of earth history i started in collaboration with the late john hayes to do geochemical work on those samples so yeah uh 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 i could make it work okay i was wondering about how you how you balance that i was also wondering whether um the opportunity of at oberlin you know teaching during the year whether the summers um became a key point for be able to do field work or uh and and when and where and if you did that where the funding came from yeah i mean one of the great things is that uh 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 and so they were very interested in finding things that they could fund somewhere in the heartland and so i i benefited from that so i did have uh nsf funding uh while i was at oberlin and actually started working with nasa on that time scale as as well so you know to do a a certain amount of of meaningful research uh i had the support of people at oberlin i had had some funding um but i do 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 you know i should say that i i know a lot more people at overland who just thought they were the most lucky people on earth and yeah i'm sure 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 the most central thing to my professional life will will be this this institution and you know i figured you know harvard was not let's be honest famous for tenuring junior professors at that time but i realized that if 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 then put that point and said well i tried it and it didn't yeah and it's not a bad place to ju to jump off from if you have to oh yeah yeah and yeah no it and your point about it's interesting your point about the liberal arts college you're absolutely right i mean i i've i've in various times my career had these positions where i visited liberal arts colleges and gave lectures sigma xy and phi beta kappa kind of thing and it's amazing to see the people who are you know it's if you're right there's their faculty who are so dedicated and and involved in teaching and and thrilled and and the small liberal arts environment is such a different environment getting to 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 uh you know my daughter my stepdaughter didn't go to liberal arts college because they were kind of they 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 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 and it's not all and you as an economic 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're told where to go um 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 what 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 in some ways that is kind of the way you know you make your bins uh it turns out that i was hired to uh succeed my mentor the late also barghorn who was hired in the 1950s as a paleobotanist and so that that's what they were looking for and that was in the biology department and you know in many ways i'm glad that that happened because a you know for most of the last 40 years i've been a member of two departments 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 i think brought um much more richness to my research on on the earth oh yeah absolutely and it let me ask you a question that 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 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 uh and earth sciences i think the other important influence on me as an undergraduate came further along in in my undergraduate life when i i just took a course it was called something like an evolutionary survey of the plant kingdom and it was you 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 margulis's uh hypothesis that the chloroplast originated as a free-living cyanobacterium or photosynthetic bacteria yeah we'll get 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 uh 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 uh the origin of animals and so it was really thanks so to lynn that interesting i discovered this world of early life early earth and that's then what i went to do in graduate school oh okay uh okay and lynn yeah as a part my first year in graduate school uh i was sitting at my desk and barghorn comes in with this relatively young woman and says andy i i think you should meet lynn margulis and to me it was kind of like saying here's joe dimaggio yeah yeah wow yeah that was wonderful she was a friend for 40 years oh really that's great and and and she was a great scientist and i happened to also have been the wife of carl sagan and and who was a who uh had a good career in in popularizing science and uh and um 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 then um i tell students that i mean the whole point of being i 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 i and even in in the kind of physics i do i i've taught 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 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 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 uh everyone should have that opportunity and experience and one of the nice things about writing books to the public is is is to give people that opportunity and so you one hopes that you know for everyone life should be a lifelong learning experience and and uh and 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 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 um we're going to be in trouble yeah you know i 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 and public uh explanations of science was what i call the received wisdom yeah you know uh they're it's almost you hit 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 and make sense of those and and i i think you know in all teaching this question of how do we know what we think we know is is really important because it you know it 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 um and you know if you actually know well here's here's what we know here's how we know it now give me your your story in equal detail exactly and and you know because it's it you the appeal to authority is just 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 is incredibly warm and i've you by the way you know i used your book in my in my i used in in classes that i taught um a lot because i i like to teach uh 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 were writing it in fact um the uh and and it 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 to say these crazy things actually happen and and as opposed to sort of geology also some of the things that we talk we'll talk about are very non-intuitive um also and 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 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 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 um which which uh which presents this beautiful sort of understanding of the interplay between biology and geology and and and uh and the and it's and and the other thing i guess which is really kind of neat about it that i hadn't appreciated so much before so i i learned some 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'll 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 um the fact that the earth evolved in around in in a solar system around the sun in an emerging environment is of incredible importance and the and the the um 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 in in the last 50 or 60 years um obviously i can't go through all of that in detail with you but there's a few things i wanted to to um talk about one is is of course the importance of meteorites of understanding um the materials that came to earth why don't you talk about the early formation of the earth in terms of meteorites and and yeah it turns out um 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 uh between that are older than four billion years old although there is pretty much consensus that the earth originated more than four and a half 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 materials 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 uh beautiful beautiful uh entry into our solar system as it was as it was forming and and you know 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 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 that really record the earliest history the socialism and by the way you said consensus but i worry about people thinking that sort of scientists vote on things there's there's really good you know especially when we get to climate change um it's it we we know that the age of the earth to actually and the age of the solar system is really high accuracy 4.54 billion years it's not as if it's i mean there's top many independent ways of knowing it so i don't want people to get the impression that it's just some some thing that we that's that that we vote on or anything but but these oldest meteorites that uh come the carbonaceous chondrites i guess that come from out of our 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 were amino acids in in these things i remember wow that was i don't know when that was first first discovered but i remember learning about it was really maybe yeah it was a it's and that alone hey that's highly suggestive of something important it may be it very important as we try and understand the history of life and earth not just that the raw elements the carbon nitrogen and and you know phosphorus and other things came from these meteorites which were building up the earth but also that maybe even primary organic molecules that were very important for perhaps jump starting life on earth already pre-existed 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 is really cool is it's possible that some of those materials may have actually survived in their trip to the earth as 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 and and we'll get to that when we talk about the chemistry of life a little bit because um you know one there are many questions about the original life and i've just been writing it actually about it in in the new book i'm finishing but you know it's not only how but where and it's an interesting question what i want to talk to you about in a bit but so meteorites help form the earth but they give us this information about the earth and we will 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 i think 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 we'll get to that but hold which i was reading in the new book um the the um not only was that material important for understanding than how the earth formed but the way the earth formed is something that's also important that there are layers in the earth that were first kind of realized and one and and you might 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 um you're right if you if you cut the earth in half um 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 surrounded 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 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 you know aggregate all of these things together by gravity you get heat produced there must have been a much higher concentration of radioactive uh materials at that time they produce heat and the earth melted and the heavy stuff the iron went down into the center the mantle uh formed around it and then through time parts of the mantle differentiated to give us this scum on the surface we call call continent so it really is it's a planetary process and once again um because of the the outcome of that the uh physics of the core gives us a magnetic field which is important yeah i was going to ask you about magnetism but yeah um the the properties of the mantle allow it to convect which actually really is the motive force uh 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 well we'll get i want to get to mars at the end too because the differences between mars and 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 think and um the you know there i was thinking about this in when when i was thinking about the early earth and the molten aspects um i didn't i don't see this as an argument maybe you can use it but i think if people are are suspicious maybe it wouldn't work because it still requires some belief in science but um are suspicious of the fact that the earth was molten um uh in my early research uh actually when i was still at harvard um 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 nature called neutrinos and i discovered that um hey new the earth is a rich source of 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 that i didn't have any idea of the time until i did my research was that most of the radioactivity 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 earl rest of the earth as they were in the surface the earth would be much hotter than it is and the heat outflow from the earth to be much greater and it shocked me 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 they shouldn't they fall towards the center like iron and then i asked someone who knew chemistry and i 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 radioactivity is concentrated in the south of the earth is kind of proof that it was molten is that is that 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 uh since different minerals actually melt and crystallize at different temperatures what happens is you start with a material called basalt 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 uh elements including many great radioactive isotopes in the in the uh the surface now that said uh i think we all agree that the earth's interior was hotter yeah early on than 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 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 outlawed they were outliers and the people who claimed to me that okay they were outlawed yeah now the earth has cooled through time yeah and by the way that process of of 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 and you you get rid of the impurities by by refining it that way 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 um and it's increasing incredibly important for understanding for dating that early formation of the crust and understanding processes related to um the chemistry of auction in the early earth as well and um and i wanna i wanna know if you could take me through that and i'd and also take me through um your own uh uh research in that regard okay well um it turns out that while what i said earlier that there are no terrestrial rocks older than 4 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 that uh are along the coast now were basically eroded from the white mountains uh some 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 that those mountains and zircons are the geologist's 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 right yeah that's the beauty i'm glad you brought it up because the 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 of uranium and these things i used to liken them to the flight recorders and 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 zircon is so stable i i think it's a they have a very high melting point um they're not easily changed by pressure either so um and it's not easy to have actually exchange materials you know in solid state between them and and their surroundings and and so the result is that since we know from modern processes and and younger geologic times the kinds of physical circumstances that give rise to zircons we can actually use those to look backward into that that dark age and you know there are zircons that go back to about 4.4 billion years so 4.4 billion years that's that's amazing yeah within 100 million years of the of the earth forming which is amazing and we learned some things which from that in a number of ways and we'll get to some of the more maybe controversial things about that but but um you all say the chemistry of 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 um the the mineralogy or the chemical structure of zircon is zirconium silicon and four oxygens and so oxygen is part of that that mineral lattice uh oxygen comes in three distinct flavors uh their most oxygen is oxygen 16 with uh 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 um analyze materials and see the ratio of these these ions and it turns out that that provides a 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 formation earth that there there's liquid water and oceans potentially and that um that itself is surprising and the and it's surprising when you when you you point out that the that meteorites and and and um are not only help build up the earth they're 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 was something like a thousand degrees in that region i think is is a rough temperature in the early solar system you don't have water around um or you know and and um and yet we have a a a a a water covered planet to first approximation and um and the question of course that arose early on and and 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 um we tend to think of water as this liquid or or an ice but there are a lot of minerals that actually have water in their crystal lattice you know a good example is gypsum everybody's seen plaster of paris and things like this and that's a calcium sulfate but its whole formula is calcium sulfate dot 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 um you know it was not free-flowing water and then as the earth accreted and started to heat up these and other volatiles were sort of released and degassed up to the surface and the atmosphere of course and the early atmosphere yeah that's right the the the liquid and and uh gaseous surface uh of the earth both came from that 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 it turns out the amount of water you can actually stick in the mantle varies with 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 a airplane around the earth 4 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 to me when i read that in in actually in the new book that 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 there 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 but anyway as i was is is is that while it makes sense that water came from from um 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 have certainly been enough material enough comets bombarded the earth since its formation that you might have populated the oceans with that um with those comets but we know they didn't and um and and we know they didn't uh because of of looking at 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 um you know a major reservoir of volatiles uh in the solar system is is comets and fred whipple called them dirty snowballs yeah that was a great name um 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 the view is 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 percent of the water came from comets and and so when it this seems at least from my understanding of what i learned 25 years ago versus now um this recognition that the water did come from from from meteorites that must have been growing and when when sort of when did that really be understood when did the isotopic analysis of water on on meteorites be such that you could say oh that that isotopic abundance com 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 like i can't vouch that there were no earlier papers but well if there were i mean it could have been many earlier i would have heard about it in 2001 yeah well you know 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 uh tell you about all sorts of different things so you know reasonably enough people started looking at the isotopic composition of materials like like uh meteorites i think the the the hardest thing was to actually get samples of comets that you could you know 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 comet'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 uh has wayne and and where does and just so people know where do we get the i mean we don't have comets here well you know you look hold your hands up so where do you get the material from comets as near as i can tell you got to go out and sample yeah and it's so so it involves space-based uh sampling now i gotta say in in light of that that one of the fun parts of my my life was to actually work on a mars mission and talking with the engineers at jpl you know makes me reconsider this oh yeah 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 it's quite amazing yeah i've been yeah when i was at jpl it really yeah it makes you want to grow up and be and be one of them and it's really an amazing um you know it's 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 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 um there were enough meteorites and comets bombarding the earth early on that they were oceans would have evaporated any early oceans very very early oceans but by the time these er 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 third yeah yeah but rather there's a very high commentary or a meteoritic flux um as the earth is forming and then it just kind of decays so there's still uh you know if you go and look at uh sedimentary of all and volcanic rocks that are three and a half billion years old you will find evidence of you know impacts so they 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 the cells of australia which is really something to think about but but you're right uh 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 you know if you go out and you know look outside your house today uh the 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 either 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 um you know around 3.9 billion years or something there was some thought that there was a a period of a peak of bombardment that fell down after that yeah that's been an evolving subject i mean this is uh and correct me you may know more about this than i do but the 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 you know the materials that astronauts picked up on the moon yeah 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 starfleet 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 uh at 3.83.9 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 uh 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 it still works but it works a lot more easily if you you know say it happened to 4.4 billion years yeah yeah so the question of whether or not there was a discrete you know and transient in increase in the meteoritic flux i i think is very much under discussion um but i think this to the extent that it did happen it may well have happened before three point eight or three points yeah you know the reason i brought up it's a it's an aside it's just important to realize that that you know what we know is determined by what we can see sure and and sometimes in certain areas you know you you develop a picture based on one one set of measurements in this case from the moon the astronauts in the moon and there may have just been a big impact then and you're and it's easy to be to to realize that or to forget that your influence selection effects influence you a lot and and uh it's important therefore to realize that when there's one set of data you have to be skeptical and uh um and you know i i i like to say to people if i happen to have been watching a basketball game in and a meteor hit and and killed me and all the people in the in that basketball and and archaeologists millions of years now unearthed us and they found me and uh and a basketball player and that was the only sample they'd say well they're 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 but um sample size is a useful thing it's a really and 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 i'm in the areas of physics i work in it's great to have 10 billion events but but uh 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 learned about this time is not just that there was a 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 what i did you're you're either too kinder yeah anyway but uh you know 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 in the earth would have been frozen over if it hadn't had a massive greenhouse effect due to that huge carbon dioxide in in in the atmosphere at the time yeah no that that's exactly right um we we only standard models of how sun-like planets sun-like stars evolve suggest that they should become more luminous through time um and when you run that backwards uh 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 a unsteady thermostat yeah exactly earth which you know in some ways you know people always talk about the origin of life you know here 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 formed but that it's persisted for four billion yeah exactly that's not a given yeah so as 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 say is is determined by a number of things and acts as a thermostat for the earth and we'll get obviously going to get to life but it it is really remarkable how how um 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 yes and 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 uh plate tectonics that the earth's um surface the crust has a particular characteristic and um which again was you know in the history of science was relatively recently understood and and first uh ridiculed when it was first proposed that that the continents were moving around and and uh and uh were different forms but now form an essential part of understanding of the history of the earth and life on earth um and maybe you could just walk us through that a little bit in particular something you point out that the the plate tectonics themselves was essential in a way for also the early evolution of life so and let me let me let me jump and say one other thing that i meant to say earlier this this decrease in the bombardment of life on earth over the first hundred million years is really fascinating because when you look at what potentially maybe the earliest forms of life they occurred about as early as the laws of physics would have allowed the the bombardment to have stopped and that either that's fortuitous or it tells us something about the ease of life evolving so but but plate tectonics themselves played a role in that so maybe i'll talk about plate tectonics first but i will share one little uh vignette on how hard or how easy is it to make life i years ago i was at a meeting and uh stanley miller one of the real pioneers in chemical evolution experiments was giving a talk and someone asked him 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's i think a decade's probably too short you know maybe a thousand ten thousand years and if you can't do it in a million years you probably can't do it no well 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 determinate chemistry that would happen on any planet that had the chemical and physical makeup similar to the earth so that that's that that's very important and we'll get to that because obviously one of the things people are interested in we'll talk about later and i want to talk about near the end is the is life elsewhere and and 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 sure 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 um uh uh uh let's go back to okay so so plate tectonics uh as you said is an idea that has really become a convention you know in our lifetimes uh it it goes back to earlier in the century particularly through the writings of a german meteorologist named alfred wegener 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 uh 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 uh in beginning actually with uh 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 um and then gradually through a series of 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 um this is called subduction zones and so between about 1965 and 1970 this went from heresy to a a broadly illuminating view of how how the earth works uh you know there's still research going on but it's it's not on the fundamental question of is there this convective engine in the mantle that really uh 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 uh so it's not a necessary part of planet formation and 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 when plate tectonics began is a good way to do it and and part of the problem is that the way it's often stated you get the impression that you know 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 [Music] but it also provides something of a of a dynamic system for rejuvenating the earth's 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 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 and the earth and volcanoes versus humans that that that carbon cycle which is incredibly important happens over you know and i again i remember in 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 ten thousands the rate at which we're putting it into the atmosphere if you if you that carbon cycle i think it's something like 0.01 gigatons uh per year or something like that uh or 0.03 or something yeah i think the important thing is is what you said you know i 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 lust 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 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 and and we and our production is somewhat similar to another event that you played a key role in unraveling which is a permanent extinction which i hope to get to and and um so we'll get there um uh i hope um the i always like when physics can be used for something so one one of the ways i want to at least um mention that one of the ways we can compare what they prove for people who may not believe continents are actually drifting is magnetism and it's a lovely a lovely factor so maybe 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 uh 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 of those two observations these people actually mapped the distribution of you know the point the way that the magnetic minerals were pointing uh as you moved away from the mid-oceanic ridge and you see these strips of magnetic uh coherence you know close to the close to the uh um 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 the sea floor is slowly getting larger from its source of that ridge and you know you can actually use um satellite observations now to to demonstrate that you know boston is getting farther away from london by about two and a half centimeters or an inch everywhere every year moves at the same rate your fingernails grow i'm told but basically yeah yeah and uh yeah the this wonderful fact that the earth's magnetic field flips which we still don't understand and i would had more time i talked to you about it because it related to the physics of presumably of the molten core of the earth um uh but it it whether we understand it or not it happens and it gives us this another kind of chronometer um and uh um uh so it it uh yeah any and it's it anyway it's interesting you could also measure the econ that continental uh drift and a number of other ways with sophisticated um physics experiments from gravitational waves experiments to cern can allow us to to measure that two and a half centimeters a year it's a kind of a neat thing and it's important to realize and i'm going to stuff over it although we might get to it when we talk about life on earth that the 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 have that motion has produced a time super continents pangaea and other things and they've affected they've affected the evolution of life we'll get to in in big ways and there's a period of 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 i i l and it's it's related to the albedo of the earth and where continents were at the time and i i point that out also because when we talk about the possibilities of life elsewhere in the universe and and planets elsewhere people talk about habitable planets which are mainly planets that were in a region of their sun where there could be liquid water on their surface but i like to point out that since the you know the earth is a habitable planet but 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 it's a far cry from being able to say we have any certainty that there's liquid water on those systems yeah and and we can talk about this more later but you know i think we have good geochemical and and 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 and that has real implications for how you think about uh life on another 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 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 north america beneath the sea of japan things like this and and there are also places where it's pretty clear that uh two continents have collided um so india moved north rammed into asia and now we have the himalaya and and so the the explanatory power of plate tectonics is is really quite astonishing yeah no it's it's and and it's important as you say it's important it's not just explanatory uh utility but also its impact on the fact that there's this interplay between life and the earth that is that goes in both directions and uh and so it's a i want to now move to life another area where you've had obviously a huge impact in your research um by by merging biology and ecology and geology and i want to talk about that uh and we won't be able to do it give it its due course because i don't want to keep you here for eight hours but um although i'm i'm fine with it but um anyway uh the so yeah i 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 probably used the wrong materials um but it was first realized the first time you know life seems like a miracle until you discover it may not be and um and one of the ways to discover that is that that natural pro 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 yuri experiment so maybe you talked about that for a minute yeah what um when stanley miller was a graduate student at the university of chicago in the 1950s uh was working with uh nobel laureate harold urie 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 and yuri's thought of what an early atmosphere might have looked like now even at the time they did that there 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 flasks becoming brown and after a couple days when they looked at what was in the flask they found amino acids the building blocks of proteins and and other things and and what that showed was in principle 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 the principle still holds and and you know 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 um you know you're sort of knocking on the doors of biology when you have things that can uh 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 uh a deep understanding of it yet but 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 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 yeah 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 constitution and in fact as understood that's a wonderful introduction to what i wanted 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 as you point out there's been a tremendous amount of work since miller urey there's still a lot of work left to do but um 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 i guess i i think of it in my own kind of course and heathen way uh as just thinking of the fact that uh of life is kind of controlled burning and if there's lots of oxygen the burning happens before the life can do it um and and and so maybe that's the way i i tend to think of it as oxygen if there was a lot around then there were energy available to make you know for 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 i think if you're looking for a planet where you can originate life the last thing you want to see is oxygen it's a great poison which was a shock to me when i first realized it um the uh the the interesting thing is and i want to just jump i mean because i don't want to spend so much time on origin life studies i want to talk about the work you've done that on on under where it really did happen life did originate on earth and how can we learn about it but but it's fascinating that um there's a question i want to ask you because more and more the understanding of 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 with because 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 and john sutherland and his colleagues at cambridge have done a lot of work on that but one of the things that interests me because it sort of confronts what i used to think of the as the preferred place of life to form is that um i was listening to john sutherland talk recently and and is in the 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 to throw that to you to see because i'm sure you're more knowledgeable about than i am yeah you know when you uh talk to people interested in the origin of life there are two uh communities which i think are licensed to shoot each other on site uh there are the people that you have uh 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 you know rnas could both carry information and be replicated and have function gets you around this chicken and egg question which came first proteins or or nucleic acids and you know 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 evolve 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 um they are the people who like the idea of hydrothermal yeah sure rigid there's lots of energy natural chemical gradients yeah 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 i mean 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 ridge with all its hydrothermal vents is above sea level yeah and you have lakes so if john sutherland and jack shostak and others would like lakes that wet and dry if they would like sunlit or radiated environments um that is not something that precludes having the advantages of a mid-oceanic bridge and the same thing is true if if uh 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 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 oh that's fascinating that's a fascinating picture actually but 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 and uh and and 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 to merge 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 produced metabolism and that shift to me i think is the most is the hardest thing right now when i think about understanding no i i think that that that's exactly right that's consistent with with what what i was saying and um you know i in some ways i'm optimistic that uh 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 with them and then maybe that's trying to tell us something about what early metabolism was like yeah yeah it was a fascinating subject but 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 made uh important uh well groundbreaking developments and that's looking at something i guess um 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 spitsbergen um is to realization that if look at looking at this stuff called shirt if you look at it they're actually examples of really early life i think it's called edicarian life i'm i'm i'm not good at names which is another reason i couldn't do geology but but uh i don't can't remember names very well but but uh that um you know that before fossils everyone thinks it's fossils trilobites and all these other nice things that the big discovery is that there was lots of life before that and and you can try and follow it back and that there were microfossils and they take us back maybe not just 500 to 700 million years which i think is where your early work first illustrated that but maybe back to 1.6 to 1.8 billion years and maybe even to 3.8 or 4 billion years so could you just talk 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 that the first person to show that there was evidence of microbial life that long predated animals was my mentor elzo barghorn um and and i just thought that was that was fascinating you know everybody knows they're 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 four and a half billion years old and so if you look at comparative biology and you know trees of life for phylogeny so called that are based on comparisons of molecular sequences in living organisms they suggest that animals should be late comers 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 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 by built by bacteria and they're they're all over the place the sea floor 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 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 of the earth so we can use isotopes of carbon for example to you know investigate the history of photosynthesis could i can i interrupt you for a second because i'm i'm wondering whether i don't know if it was your research that would push this but it's looking at isotopes of carbon that can be very important to understand the early history of life and i want could you and people may not realize why so if you could just and am i right that you you were some of your i played a role in some of it again uh you know most of us have stood on the shoulders of giants 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 a small he was never humble and he was never nice just so you don't don't 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 one percent 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 the 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 uh they actually discriminate so that they preferentially incorporate carbon dioxide that has carbon 12 relative to carbon 13. and the distinction for 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 organic matter in them and if you go to these rocks in spitsbergen that i talked about or these rocks from southern africa behind me uh again yeah 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 i want to get to auction but they're incredibly important and they and and i guess i'll jump through the the details of of the spitzberg and then seeing it at one as you say 1.6 1.8 or 3 billion in australia and and and these old rocks you're looking at in africa le i want to ask you so where does the controversy stop i mean i've heard first i've heard of you know about four billion-year-old evidence of microfossils i just was reading about 4.28 billion-year-old evidence in quebec um is is that accepted is that controversial what's the deal yeah it's controversial i i think that um most people would agree that an actual set of you know well-preserved sedimentary rocks that are three and a half billion years old on several continents you've got both physical and chemical evidence that suggests you know you had a microbial carbon cycle a microbial sulfur cycle so early life was a going thing at the time now you can go back to metamorphosed rocks metamorphosed sediments you know they've been subjected to high temperature and pressure and they still have um carbon isotopes that suggest that there might have been a biological carbon cycle although if you you just don't have quite the confidence as you have in these better preserved sedimentaries well that's there's some little bit of carbon that's seen in zircon again right is it uh in one zircon yeah there is one bit of of graphite just carbon uh in it and first of all that that is a analytical turret of force 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 and that's their entire state the miller uri 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 about saying that um 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 i don't think they particularly advance the question uh 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 it's selection effects it's in fact we have very the older back we go the less evidence we have at least here on earth which uh which you know maybe we'll be able to find lots of more samples elsewhere but i hear an 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 so we didn't 4.1 4.1 is uh 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 her life goes back to 4 billionish years whether it's 4 billion or 4.2 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 when when and and that 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 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 um it'll be and 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 um yeah no you 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 to write 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 an early evolution in life um 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 the bottom line for the geologic record is that our modern earth in terms of both its biological diversity and its its you know environments that we 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 percent of our planet system yeah and in fact okay and that's wha that's where i want i want to go next to this other surprising fact of of of how life has changed the 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 dipped my toes in this water 25 years ago and then and to come back and see the the um how much knowledge there's been in in in terms of of that period of of of what's called the great oxygenation event and really how great it really was and and and the history of life and of oxygen earth which i think is important uh to get to where i want to go next how would you feel about taking a break now and doing it later today or or another day to do that last 45 minutes so i wanted to find out about your time i i think it might be easiest if we i'm happy to talk for another 45 years it's a lot of fun uh it might be easier to schedule it and do it another day i think so it'd be easier in my life and i want to but i want to schedule it pretty soon so so while we're fresh but i think this is fascinating and again i hope you're enjoying it i bet i hope that you're finding it um yeah yeah this would be amazing it really it would be 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 i'm 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 facts fascinating because when we last spoke um um we were in a in a a an earth which was which was still essentially oxygen free and um and life had begun but um but uh just the beginnings of life and and and the thing that really changed with life where life changed the earth and then and then the earth changed life is is the rise of oxygen in some sense and um um and and i i want to reiterate something we said last time which i mentioned which i which was a sentence in your book which really hit me as as really important that that um uh prebiotic uh chemistry doesn't work in in in in in an oxygen-rich environment and and therefore no oxygen once again was very important in the early earth but then of course it changed now the 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 and that is the history of oxygen in the earth uh i had thought by two billion years ago oxygen was almost at its its current levels but my understanding is now that it's not and and uh 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 you could talk about that a little bit yeah there's actually a variety of geological signatures that tell us about oxygen history um 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 chirp 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 they're bad one thing these banded iron formations does that indicate that there was fluctuations in in oxygen at early times as well or no uh pro probably not there's a variety of ways you can get the sort of banding on levels from you know millimeters to to centimeters to meters that you see in these rocks and uh although there's there's every reason to believe that oxygen levels may have fluctuated on on the early earth both in time and space um i 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 what time again yeah 4.4 out of 4.2 and this does look like it's something that you know tried a couple times before it took permanently so uh 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 asked i think you said 4.2 and you meant 2.4 2.4 sorry yeah yeah that's okay good okay okay it was 2.4 to 2.2 before that we were definitely auction free there was also i i was always fascinated with my kit when i was a kid about pyrite and pyrite also plays a role in our understanding of this as well of the auxin 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 and by 2.2 billion years ago that signature is gone and it remains gone to this day so it's a it's an independent signature independent of the signature from iron yeah it's not well it's always nice to have two two independent measurements of different uh that are consistent it gives you confidence yeah in fact there's four or fives and they all give the same answer which is good now the 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 um uh 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 could either use oxygen or in these other environments hydrogen sulfide right and and and so there's this interplay between environments yeah i mean there there are for organisms that like us ourselves are heterotrophs that is they take in organic carbon and then uh oxidize it to 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 um and and so as oxygen started to accumulate in the atmosphere and surface ocean the inventories of things like sulfate and nitrate also increase 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 is 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 um i 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 2.2 looked huge yeah and then the other 99 today looked very small but 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 become fairly widely understood in the last 20 years or so yeah i know that's what i'm saying before before when we first talked which was about this which is more than 20 years ago or at least 20 years ago i was under the impression that things went up quickly and and and and yeah and now i understand it sort of didn't it it was at the one percent level for a long time yeah something like that and then uh there's a second event you know which interestingly enough as we'll talk about coincides with the rise of large modal animals yeah uh 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 an interplay i think i mean the chicken and egg and i i was going to ask you that question i i mean i'll wait to ask you that question because i want 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 i've made some contributions but so have have many other people um i i think one interesting idea which i credit the lab of don canfield in 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 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 of these other kinds of photosynthetic bacteria are likely to be the ecological dominance and under that those conditions uh 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 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 as 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 uh weathers from exposed continents and volcanoes and enters the ocean so one of the things that looks like is happening now and this is you know something that's evolving on almost real time is the idea that only uh 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 that that it was far you have this rate limiting step and you have enough phosphorus boom you get these the oxygen producing bacteria cyanobacteria and the fact that it was related to continents it it kind of interests me because you think of life influencing the earth but and this is a clear case where where the earth is influencing life and it did remind me of of the sort of in some sense this gaia picture of 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 uh i think there's also no question that at this pivotal event in earth history the initial rise of oxygen uh it takes both physical and biological processes to happen it's not that one dominates over the other yeah no that's that's really interesting to me because and then hit me that i used to think it was a natural consequence of sort of of of early stages of photosynthesis that oxygen would rise but this competition that you can get uh electron donors or or electron takers i should say uh from other parts of the environment is really kind of interesting and 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 uh when there are other electron donors present cyanobacteria don't compete very well so it you know 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 coupled change in the environment well you know that'll come later i want to talk to you later about life about our 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 crazy liquid water but but by this argument if you had a a water world which had no continence that might be an impediment to to to at least uh uh producing advanced forms of life because you wouldn't have those oxygenation events well yeah uh 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 um and and 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 uh um is that is that true yeah and and one of the reasons for that is that fundamentally eukaryotic cells which are cells with nuclei like in our own bodies uh have a little organelle called a mitochondrion which is where respiration actually happens and it is now fairly clear that the mitochondrion evolved 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 these uh mitochondria are fundamentally uh respiratory yeah their oxygen where and now they're in our current cells they're where the oxygen all the action happens with oxygen that's right making it in usage and and and and now that might so that that kind of engulfing that kind of symbiotic engulfing or may you be called cannibalizing the benny bonhomme we want to talk about it um we talked about lin margolis uh you talked about in the context of chloroplasts i think but did she i always thought that she that that the mitochondrial um merger was was also her uh but it was it someone else yeah well yes lynn did talk about both mitochondria and um chloroplasts 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 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 lin uh was very much an advocate of the idea that mitochondria were symbionts now so so you've now got these mitochondria and eventually have multi-cellular systems and 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 maybe it's obvious to everyone else but it occurred to me and i thought gee that's 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 uh respiration relative respiration using oxygen using oxygen gives a lot more energy than respiration using anything else or fermentation or any of the alternatives of being a heterotroph so oxygen yeah using oxygen and respiration really gives you a leg up in gaining energy from taking in organic well saying a leg up is appropriate because what i was going to say to i mean it's unless you it's it's clear it's it's not an accident it seems to me that animals emerged you can't have you 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 is it 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 uh probably 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 i don't think you would see a tyrannosaurus unless you had the kind of energy that only oxygen can supply yeah and and the animals so you have so you went from bacteria to algae to some extent an algae or 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 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 to into being around six or seven hundred million years ago in which algae our major primary producers that requires that there's more nutrients and so i you know one of the ideas we put forward uh is that this is an another jostling of the phosphorus cycle and that that then has a it produces more the algae take over in in at least coastal environments we have more oxygen more food and together those two things provide a new world in which large heterotrophs like animals can do yeah and it's sort of a feedback because more more food more algae more algae more oxygen and and it goes and it continues that way it's sort of a positive feedback and it's yeah that's really important because uh 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 you know influence you go back to where you were so you're absolutely right that this positive feedback is a key thing and then and and so oxygen achieves its current levels or close to its current levels you see about six or 700 million years ago well it becomes a lot closer to today so you know having had you know what a billion and a half years or so in which oxygen was maybe one percent of today's levels you go up at least to 25 30 or 40 and then fro most people seem to think and again there's four or five lines of evidence that uh suggest this that oxygen reached more or less it's its current levels probably around 400 million years ago something like that okay now we went through this world of dominated by well bacterial world to world with algae but but it's not fair to say that i mean it's i was going to say a world dominated by that but in fact you present a number which is is kind of uh 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 um i i always tell my students that we are guests in a microbial world yeah and and that that's true on so many ways uh only bacteria have the diversity of metabolisms that allow them to 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 um yeah um you know i think we always think animals are important because we're writing the history but um you know animals were added to ecosystems on earth that are fundamentally microbial in all of the circuitry that runs the ego yeah so it's fair to say well in some ways we change 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 of of microbial uh life that's been around for as almost as long as life's been around yeah basically now but there are let's talk about the peaks so i want to want to move to um as we think about the animal world to the to another place you talk about which uh with with great love and um and it's a place i i've heard about and i can't wait to visit it's mistaken point in newfoundland um this important um well let me let me before we get there it's 565 million years ago um and and you talk about the these weird and and wild animals and it does look very science fiction like when you look at the at the at the uh fossils from there but before that between the time rise of oxygen and then is the snowball earth time which we talked about briefly before and i i don't know i think i i asked you this when i first 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 thought of it but um snowball earth was a dramatic event because it separated the atmosphere from 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 the cambrian explosion whether you know whether well the way to put it is disasters or or crises on earth which get rid of vast populations in some sense produce an evolutionary opportunity for other things and so the question is if there hadn't been snowball earth with this kind of transition and this explosion of new kind of life happened or or was it possible because of the of the 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 vestiges 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 some 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 surroundings so it it may well have played a role i don't think we have any detailed understanding of precisely what that role might okay now okay that's good okay but now we have these explo sort of semi-explosion of interesting animals you see at mistaken point and um and it's and you talk about um this sort of uh interchange of carbon and oxygen and um and the kind of animals that were there and where how they're 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 they have to be thin so you want to explain that yeah the the animals that we see in the so-called ediocarin period uh 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 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 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 placozoa which are you know just a couple millimeters long not much more than a upper and lower surface with some sort of gelatinous material in in between but in fact that might be the last you know vestige of what was a predominant type of organization in early animals and and these placozoa if you look at where they fit on the tree of animals they're right in the right place uh right near the bottom of the tree so it i i don't think we're looking in this early record of animals of something that represents 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 um 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 the the this first radiation of these weird animals of the and i'm and and i 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 mediocre adiocrine i had the c 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 that people argue about it is interesting that the world of these weird and wonderful animals goes right up to the end of the ediacaran 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 uh perturbations at that boundary that may have actually extirpated them at least 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 and back the top and the bottom you know organizations that we're more familiar with uh things are motile 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 the cambrian world and for the first time we see body plans that are still familiar you mentioned trilobites and the arthropods we see mollusks coming in um basically the cambrian period is the time when nearly all of the basic types of body organizations we're ever going to see and animals take shape a very so it's a it's sort of the real precursor of the modern world in a sense but but 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 the i mean could it not could it be simply having the reason these other ones disappeared as they were good food instead of uh life plans chain are they it certainly may have played a role sure um 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 talked about the green world basically when now you have plants beginning to you know when you have continents up and you have plans beginning to transform the world and um and uh 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 uh 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 of green or blue green because there were microbial mats yeah in wet areas on continents probably you know as long as there have been continents but remember that you know in a sense plants are green algae with a college education basically and they uh you 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 most molecular clocks would estimate the time of origin of some of these features uh suggests 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 uh yeah which is now the um essentially the modern world and and i want to move ahead because i mean and of course you we cannot and i think you talked about it once we cannot mention the animals in the modern world without mentioning dinosaurs um and because you know they're the interest when you think about early life especially for kids but for adults too dinosaurs of in a in a um which began and dinosaurs emerged around the time same time as plant life no um in fact uh dinosaurs are fairly newcomers they the oldest dinosaurs i would say are about 240 million years old and 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 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 uh you know die by this well that's right 66 million years ago another extinction well now you've you've done this uh segway perfectly for me because i want 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 exchange we all most of us who think about extinctions know about the dinosaur extinctions because we know about the you know the big comet or meteor or whatever you want to call it that hit in in chick syllab and and 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 uh but you're i mean i wouldn't say it was a pittance the the 166 million years ago was a major event in the history of the law of law 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 percent 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 an extinction that may carry a more important lesson to us i mean the dinosaur one carries a lesson which is we should be looking out for asteroids if now 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 and i and i can and i know you agree partly by reading what you've written but um 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 that that we let these are history gives us many lessons and and i i people have heard me say this before but my favorite favorite quote of mark twain i think was uh history doesn't repeat itself but it sure rhymes a lot but but uh and 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 is captured in in fairly great detail and i've been to one of these places uh where you know 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 it's really quite stunning to to be there and geology cooperated in in this uh 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 it's amazing with timing now this is um i am correct that this is sort of you 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 um i won't deflect this one but one of the things that we did was it turns out there are some very unusual uh 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 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 lab in the uh 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 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 it's profoundly interesting and again it's i love learning new things that i that that have changed our understanding and that may have an impact and this volcanism is amazing i mean it's from from siberia right and and and the amount it's hard for people to realize the scale of volcanism uh a million cubic miles of of so that's putting that in perspective maybe that doesn't ex 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 uh 48 united states that's what we're talking about yeah we're talking about 11 times larger than any volcanism any human being has ever experienced and and what we and the fact that it was immense is is remarkable it happened as far as retail once i guess in 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 did it only happen once well no there are um there's a whole class of phenomena that geologists talk about called large igneous provinces or and it is the case that every once in a while um and once in a while is the order of every 30 million years or so we do seem to have these massive outpourings of 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 but it happens and 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 uh than it is at other times and so this is not a unique event it's not the only event to cause a major extinction the same thing happened uh 200 million years ago which is when dinosaurs survived and other vertebrates didn't um so it is a recurring feature yeah but it was but but 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 it yeah it's uniquely large in its in its um the degree of impact on so it was just that other large igneous 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 it was the biggest yeah it was the biggie okay but 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 realized were were endemic were were characteristic of of what was happening 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 what so why don't you talk about it yeah i know you're just right and this is something that uh really came home came home to me as we were thinking about this that carbon dioxide can kill in several different ways uh 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 that and you know there's this wonderful physiologist in germany named hansardo 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 you know 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 obviously why i wanted to focus on it but but it's it's interesting to me because this um this permeate extinction this release of large amounts of carbon dioxide didn't happen in decades in back then or or a century it was more of it was a longer term release right i mean i assume this period of volcanism it's rapid it's it's more rapid than our ability to resolve time that that i uh can 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 we are doing the same thing but not over thousands of years and so the planet couldn't one of the reasons people the the extinction happened is that animals couldn't adapt quickly enough or natural selection could adaptation couldn't happen on the time scale of of this of this uh massive volcanism and rise in co2 and that was maybe thousands of years we're now talking about a situation where we're releasing huge amounts 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 um how much did the carbon dioxide increase in the in the permian extinction um i i again this is all all model dependent but it might be dribbling something like that and so and we're like we're headed on we're 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 um a number of things i think one is uh there is a difference between the end of the permian and today in that our uh 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 uh if we have a will to do so we can do something about it so i i think what people should take from this is something of a wake-up call that um 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 you know wildfires aridity uh causing water problems for people in many parts of of the world um sea level going up um you know if you care to look you'll see that the world is changing at a rate that is faster than uh any of your ancestors could have could have imagined absolutely and and and as i like to say the basic science of it is it's not controversial simple i i don't even know if you know but my last book is called the physics of climate change i wrote a short book on just the physics and um and not the chemist well there and some chemistry of it um and and so it is there these are basic processes there's nothing these are well understood phenomena that have been understood for hunt over 100 years and are the basis of much of modern physics and chemistry um but i think the point you made which is really an important point is that 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 um we are as you say a very different kind of animal we can choose the we can we can foresee the future we can plan for the future we can be stupid about it or not but um but it's i think it's really important to say that there are there are dramatic changes and many species will not survive those changes the world will change but it doesn't mean it 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 i think that 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 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 leave absolutely and it's important you know i ended my book with the with the with the phrase from louis pasteur fortune favors the prepared mind and um and i think that's one of the reasons why it's 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 it the earth is a a textbook if we choose to read it correctly which you've done your whole act life and and illuminated a lot for the rest of us in that regard and you know i i i have to read the last paragraph of your book because especially it strikes me more now when you talked about i i asked you at the very beginning of this dialogue uh about your own interest and it was a book on archaeology and you were kind of amazed that you were standing on this on this history and i thought wow because that maybe that it really resonates with me when i read when i read the last i'm going to read the last paragraph so here you stand in the physical and biological legacy of 4 billion years you walk where trilobites once skittered across an ancient seafloor where dinosaurs lumbered across gingo clad hillsides where mammoths commanded a frigid plane 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 you sure you stood on the 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 i thought you were thinking wow isn't this poetic and at least i was thinking that but um 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 from any species or through nuclear war for our own if we're um there the 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 extent 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 set let me let me i'm pretty sure i can attribute that to you and i i know i thought of that myself but 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 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 uh or and or vice versa yeah that's right and there is certainly uh uh a school of opinion that has always liked the idea that life came to earth um from mars which simply kicks the can of origins downstream i've never i've never yet um i think at this point it's fair to say that we have no idea whether life ever evolved on mars uh we have now had through three rover missions that have looked at uh 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 uh and i think it's still worth looking for it as we try to understand the early history of mars better but you know as we're talking there's only one place in the universe where we actually know life exists and we're it and we're um and i 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 uh many of those that now looks have some sort of planetary system 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 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 and you've been yeah and you've got to find it you can you can hypothesize it about and mostly i think most of the hypotheses as i say will be wrong because nature usually surprises us but um 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 um you know that that's pretty much fun that's expensive so that's got to be amazing um i i do think one of the things and again this is isn't without some loyal opposition but uh with some colleagues we published a paper recently in which we we uh propose that while there's more evidence for wet mars early in its history that that wetness may have been episodic and 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 temperate wet conditions for a hundred thousand years every 20 million years 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 um is it not true though we're 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 if the conditions were compatible in some ways it would be hard not to pollute the other planet with life well we do know um certainly we have meteorites that come from mars yeah and we identified with uh uh certainty um i think things would go in the other direction although i would be harder the trip from mars to to earth is 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 uh again you can't say it couldn't happen but um it's it's it's probably not a really high probability so again you know i i don't tend to spend a lot of time thinking about things that uh i can't do anything about but um i i i think i 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 uh if if that's shown then uh we'll have some interesting conversations yeah yeah yeah right now it's it's uh but you're dubious but let me let me then the second last question um 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 enceladus 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 uh europa and enceladus are are are interesting in that you know they do seem to have liquid water beneath the surface and organic device and you could get you know probably a limited biomass uh in in those environments but it's it's not impossible so uh i i am a great fan of actually you know using some of nasa's resources to explore those moons in in more detail yeah no i i mean i think it's fascinating the idea because first of all we do see those guys are spewing out some of some of those moons and and there they have salts organic materials and and such and 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 it would be definitely an independent genesis of life the 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 um do you and i've always said you can send you know uh or over to mars for the price of of making a movie about sending a human to mars and and and uh that 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 um what's your what's your view of of given that given the resources of of the rovers versus uh 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 is hugely high you don't get much change for your trillion dollars when you do that so i think that that if 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 spent on that is not something you'll spend on other things eating the hungry and that sort of thing and and you're right i i think that just the increases over the 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 uh the scientific requirement of sending people up there so we will see i will probably be safely in my grave by the time that happens so i i'm glad to see yeah yeah i mean 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're the point key point on the head that that rover's technology is you know technology on earth is improving so fast and you may say well you know what geologists could do in a day with the rovers during year but a thousand rovers could do could do uh uh you know as much as it or more than a geologist could do by being in a thousand different yeah and we've actually suggested this to jpl that uh it would not be very expensive to have a sort of a a fleet of kind of mer capable rovers you know you could have instruments that switch in and out for various places but but really explore the planet i i 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 in a handful of places and so there's 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 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 them and the other point is that we don't we as far as i can see i've never sent humans into space for scientific reasons it's always other reasons and because if it was for because when you think about scientific reasons there's no reason to send humans into space if you're in a bottom line um it's adventure and other things and politics um last question quickly what's the most exciting thing in the future of the uh 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 there i have stronger opinions um i 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 uh 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 of that happened uh but why did it happen uh you know we know that there's more oxygen coming in at the end of the pre-cambrian we know that there are these snowball glaciations 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 and different types of data is 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 uh fascinating and enjoyable and 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 uh and uh thank you very much andy for taking the time thank you and congratulations once again on the prize you take care [Music] 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 cosmos 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 originsprojectfoundation.org

Channel: The Origins Podcast

Views: 119,672

Keywords: The Origins Podcast, Lawrence Krauss, The Origins Podcast with Lawrence Krauss, The Origins Project, Science, Podcast, Culture, Physicist, Video Podcast, Physics

Id: E67tjw69psA

Length: 174min 27sec (10467 seconds)

Published: Thu Jul 14 2022