hi everyone welcome and good evening my name is lauren artilles and on behalf of harvard bookstore the harvard university division of science and the harvard library i'm excited to introduce this virtual event with andrew h knoll presenting his new book a brief history of earth four billion years and eight chapters in conversation with peter gergis i hope you're all doing well and hanging in there on this extremely hot day thank you so much for joining us virtually tonight's event is the latest installment in our harvard science book talk series which works to bring the authors of recently published science literature to our cambridge community and beyond coming up in the series on monday june 21st at 7 00 p.m we'll host stanford professor of bioengineering and psychiatry and behavioral sciences carl desaroth for his new book projections a story of human emotions in conversation with harvard professor of molecular and cellular biology catherine dulac to learn more about this and our other upcoming virtual events you can visit harvard.com and sign up for our email newsletter or check out the page harvard.com backslash science for more info we also have a science research public lectures youtube channel where you can view previous talks that you might have missed and i'll post the link for that in the chat this evening's discussion will conclude with some time for your questions so if you have a question for our authors at any time during the talk tonight click on the q a button on your screen and we'll get through as many as time allows closed captions are available for this event depending on the version of zoom that you're using you may need i'm sorry you may need to enable them yourself by clicking on the closed captioning button on your screen in the chat i'll be posting links to purchase a brief history of earth on harvard.com as well as a link to donate in support of this series and our store your purchases and financial contributions make events like tonight's possible and help ensure the future of a landmark independent bookstore so thank you to our partners at harvard university and thank you to all of you for showing up and tuning in in support of authors publishers indie bookselling and especially for science finally as you may have experienced in virtual gatherings over this past year technical issues may arise if they do we'll do our best to resolve them as quickly as possible thank you for your patience and understanding and now i am delighted to introduce tonight's speakers andrew h knoll is the fisher professor of natural history at harvard university his honors include the international prize for biology the charles doolittle walcott and the mary clark thompson medals of the national academy for sciences the paleontological society medal and the wollaston medal of the geological society of london for nearly two decades he served on the science team for nasa's mars exploration rover mission and he is also the author of life on a young planet for which he received the phi beta kappa book award in science peter gergis is a professor of organismic and evolutionary biology at harvard university his research resides at the crossroads of microbial ecology physiology and biogeochemistry and as such is highly interdisciplinary he received his bsc from ucla where he also worked with doctors david chapman and william hamner he received his phd from the university of california santa barbara where he worked with dr james childress tonight they'll be discussing andrew's latest book in which he serves as tour guide through our planet's many different geologic epochs drawing on his decades of research to contextualize our current climate change crisis steve rosade calls it an engrossing witty and eminently readable romp through our home planet's 4.5 billion years
from trilobites and dinosaurs to human origins and our rapidly changing modern times and neil shubin writes in a brief history of earth knoll treats us to a 4.6 billion year detective story revealing the origins and inner workings of our home in the solar system in these pages you'll discover something profound how our past present and future are grounded in planet earth we are so pleased to be hosting them here tonight without further ado the digital podium is yours andrew and peter and thank you there we go sorry peter every time it's all good how you doing good good how about yourself i am doing grand thank you uh uh you know first i want to say uh thank you so much for the invitation to hang with you and talk about this book uh it's always a pleasure and um yeah i'm looking forward to hearing some more thoughts from you about what you got in here but i'm gonna make i'm gonna be shameless here and say this is a great great read folks so by all means uh pick it up and check it out um you know andy um you know one of the things i wanted to to sort of start with right off the bat is is uh a kind of theme throughout this book and actually a lot of your work it's one of my favorite things about your work over the years both your books you've written and your research but it's this emphasis about the relationship between the living and non-living components of our world um you know i don't mean like zombies or you know the undead but but the the interactions between the the rocks and the sea and the atmosphere and and living organisms um you know i would love to hear a bit more about that your thoughts on that relationship between the abiotic and biotic sort of in our world and specifically you know how has that relationship changed over time okay well that ought to take up the hour we're done my work here is done yeah i i have to say that you know this goes back to when i was a sophomore in college and had this hadn't the slightest idea of what i was going to do with my life and really in desperation i took a whole bunch of science courses and actually audited some others and found on the one hand i really liked an earth science course and on the other i really liked biology and in what may have been the only real insight i've ever had in my life i was sitting in my room one night and i thought wait a second these are not separate disciplines there are a lot of ways in which the physical and biological earth are are two sides of the same coin and and once i had that in my head i i just went from there and and i think that many of the problems of modern earth science many of the issues in evolutionary biology certainly almost everything we think about when we think about environments and environmental change hinges on this conversation between the physical and biological earth and that basically is written in an alphabet with only a handful of letters you know kind of c o h p s and n the the basic building blocks of life and what's important about those is that the largest reservoirs of all of those don't lie in organisms they lie in rocks in the oceans and and in the atmosphere and as i said i can't understand the history of life without embedding it in earth's physical evolution and i can't understand environmental history past present or future without considering biology so it yeah it is it's an ongoing conversation and to get your question about change it's been going on since the origin of life and it changes i think largely as the physiological capabilities of organisms change so when organisms learn to make biomineralized skeletons that changes the way limestones get deposits for example but also because the physical earth itself has changed if you had been around three and a half billion years ago and looked at earth from afar it would have been basically a water world kind of a global indonesia if you would and as continents emerge and start looking the way they do today that has tremendous influence on this conversation so it's it's a continually changing cast of characters and continually changing conversation yeah you know i don't want to spoil it for those who haven't read it or finished reading it but but the your your description and discussion of continental formation and drift is spectacular so it is a lot of fun and it really actually reshaped the way i think about it so i thought that was fantastic um the um the other thing i really like about your book is is the use of benchmarks um you know i think both of you and i i think i learned this from you andy in fact i'm almost sure i did as i uh when i came here and first started as an assistant professor and began thinking like how do you help how do we help our students understand time uh geological time and the like and being able to go to to use these kinds of familiar benchmarks uh is really useful and you you mentioned the beatles which of being a big beatles fan it was an extra bonus but you talk about how global sea levels you know sort of been rising and oxygen's dropped three percent right since you've been in sub surface oceans yeah in this right and and since the beatles catapulted to fame um and that seems i mean that's astonishingly fast on geological time scales um but i i wanted to ask you are are there other periods in earth's history uh where conditions changed rapidly maybe it's similar time scales or longer but how do things turn out for organisms uh when change is rapid is there is it more challenging for the biosphere to respond yeah absolutely uh you're correct that we live at a geologically unusual time uh a number of features of our environment temperature ph of the ocean sea level oxygenation of subsurface oceans are all changing at rates that are geologically unusual now they're not unique and that's where the bad news comes in because if we look back at intervals we can identify in earth history where change has been very rapid and profound those have been times that have commonly been actually catastrophic for organisms so my my favorite example of this is actually something that we've worked on over the years that uh the largest mass extinction that we know of when ninety percent of animal species in the oceans disappeared in a geologic instant that occurred 252 million years ago and was driven by volcanism a million times greater than anything that humans or our immediate ancestors have ever witnessed and so what happened well turns out co2 went into the atmosphere there was global warming uh the ph of the oceans went down ocean acidification oxygen was depleted in subsurface parcels of seawater in other words what happened then is basically what's happening now the difference being that rather than massive volcanism driving this it's technological humans so i i think the the message of the past is not only is our present moment in our planet's history unusual but that it brings us in contact with other times of rapid environmental change that have actually been you know famously detrimental to the biota wow a million times that's bananas you know i don't know if anybody is has how many of our of our of our audience members are those of us joining us here have seen a volcanic eruption but that to me is just astonishing um you know and on the subject of mass extinctions um i also want to call out page 137 because you end with such a fantastic cliff kind of cliffhanger you said something else happened um by the time uh glacier collapsed uh some 70 percent of all known animal species had disappeared and that really got me thinking about mass extinctions um how many mass extinctions have there been okay first of all i have to give a shout out to charles dickens who was a master of ending one chapter in a way that wanted to get you into the next one so i'm just i'm just aping dickens got it um yeah generally speaking people have talked about the big five uh and that's why you have elizabeth colbert's wonderful book the sixth extinction which includes the the present um and they don't all have the same causes uh fairly famously 62 or 66 million years ago uh there was a giant impact most people think uh a meteor although there's some cometary enthusiasts that's what killed the dinosaurs and lots of other less evocative creatures but then at least two others and possibly three of the other major extinctions are driven by massive volcanism which happens episodically in earth history fortunately uh only once every many tens of millions of years so there are more proximal things to worry about now but that happens and then the one that you mentioned about 440 million years ago at the end of the ordovician period is actually associated with an ice age now in in some ways for someone like me that's really odd because you know we have been in and are in some way still in an ice age and the level of extinction particularly in the oceans that's associated with that is pretty small so so what was different at the end of the ordovician period and as near as i can tell the difference is that when the ice sheet started to grow in what's now southern africa antarctica australia what were called the gondwana continents they started to grow at a time of high sea level and this is where one has to give a tip of the hat to our our old friend eo wilson who many years ago with robert macarthur came up with the theory of island biogeography one of whose fruits is this uh quantitative relationship between the number of species that an area can support and the size of of the area so if as has happened in our current ice age sea level is fairly low when the ice age starts yeah sea level can go down 100 meters but the actual change in habitable area for shallow water marine biota is fairly small but if you have high sea level and you actually flood the continents because there's vast sort of flat areas of the continental interior then if you drop sea level by uh a hundred meters or so you actually get rid of a majority of the surface area available for for colonization so we know that this particular ice age is or mass extinction is associated with an ice age and as near as i can tell the circumstances of that ice age with regard to sea level very likely played an important role that is a bad day you're talking you know um which is sort which just brings to mind another question off the top of my head though andy so i never really thought of this so again without spoiling you know a little spoiler alert i suppose here but you know you talk a lot about continents and supercontinents do we what do we know about the susceptibility of continents to environmental change as a function of their size is having one big supercontinent advantageous or disadvantageous in some ways or do we know that's a good question and i don't think we have a definitive answer i think it is the case that in the past say for example 250 million years ago when most if not all of the continents were aggregated into one mass that has some interesting effects on the one hand the interiors of those continents probably have climatic patterns that are very different from much of what we we see today and we see evidence of that in the geologic record and the other thing that it's worth thinking about if you aggregate all the continents into one mass that means you actually have a global ocean that is greater than half the half the you know circumference of the world and that changes physical sea water circulation as well and that has uh environmental consequences as well so in some ways we know that the geography of continents has varied through time we live at a time of almost maximal continental dispersion around the planet we know that 250 to 300 million years ago most if not all of the continental masses were uh aggregated together we know if you stick around for another 200 million years or so it's going to happen again you know you move things around on a sphere and they're just going to rip them apart but they're going to bump into each other again so this is something that has been happening for more than 2 billion years and i i think people are still trying to understand both the causes and the consequences of that that geographic variation yeah absolutely uh this will be a good time to remind uh our um uh our friends who have joined us here to send those questions in so we do have the q a um do take a moment and send the questions in because we're going to set aside some time to allow professor noel here to uh to speak to your questions directly i see we got a couple in so far so so so keep them rolling um but on you know thinking just to sort of remind our our friends who have joined us here uh well you know we have these patterns of ocean circulation today that uh support life in the deep oceans uh and in turn provide nutrients to the shallower oceans so that our ocean today is very well connected bottom to top um again off the top of my head i i you you remind me that the the if you have this sort of super continent you really different um sort of conditions uh sort of oceanic conditions do you have a sense of or do we as a community have a sense of those global weather patterns again is there any sense of what happens when you have a super continent in this sort of large expansive ocean greater than the circumference you know sort of three quarters is a conference or earth or like yeah there certainly have been models and uh i think you are likely to get a more sluggish ocean circulation particularly as was true uh for the last time we had a super continent once you have no ice at the poles then you end up having a sluggish circulation and that will contribute to fairly low oxygen conditions in in deep water environments and that could have consequences for you know cycle for example since that's really in a way driven by the uh rain of organic matter down to the deep ocean then it gets chomped up by bacteria and the phosphorus comes back up through through upwelling um that's something that works very well today um probably for most of earth history it didn't work very well yeah that is very cool and uh you know i know i'm sort of showing my true colors here with so many ocean-centric questions uh but it's you know it's a kind of reminder to all of us including those who are who joined us here today that uh um you know we sometimes it's easy to think of the deep ocean as this harbor for really ancient life uh ancient animals you know really things that may have been around for a long time and that there are elements of what you just shared that make that less likely in some ways right well yeah i mean if we look today there's oxygen in the surface waters that are in contact with the atmosphere there's oxygen in in deep waters there are there's certainly places in the oceans where oxygen is depleted and can actually fall to zero but they're you know a relatively limited part of of the volume of of the global ocean now for the first 90 or so of our planet's history most of the subsurface ocean was anoxic most of the time that's a very different world and then even over the last you know three or four hundred million years when we have had it appears a more well ventilated ocean we have these brief intervals of time called oceanic anoxic events when most of the deep ocean goes anoxic again you know it may only last for 10 000 years a little bit more but yeah um i that that's widespread enough and frequent enough that you probably have to recolonize part many parts of the deep sea floor afresh because you've exterminated much of what was there wow that is so cool and you know when we're talking of course about animals that are oxygen dependent and microbes that are oxidant dependent and that and then of course there's this whole other sort of that's not even an other world it's a part of our world but those that are the those that are the anaerobes the microbes that live without oxygen oh yeah and and again one of the things that a lot of people including us have been thinking about in recent years is uh again this phosphorus cycle and does phosphorus in seawater make it back up to the surface um you know the ease and efficiency with which microbes can actually re-mineralize organic matter and free up that phosphorus depends on the supply of oxidants and if you don't have much oxygen you won't have much nitrate you won't have much sulfate and so uh many people have now suggested that for much of our planet's history you know the earth system wasn't very good at remineralizing organic matter and getting those nutrients back up to the surface so that results again in a in a very different world and i think that the bottom line is really that the past is not simply the present with dinosaurs or the presents the past is really different and a lot of scientists have worked for decades just to try and understand how different it was in the past and how that trajectory through time ends up with what we see around us today i love that you know i am as as as you know i have a fondness for silly t-shirts i think i need to get you one that says the past is not the present with dinosaurs that makes me happy i'll have to see what we can muster um you know on the subject though of mass extinctions um i wanted to ask you this question about what the sort of potential let's call them global upsides to mass extinctions i mean the downsides are seemingly self-evident um and and we know of course that you can imagine upsides for those species that now have a chance to thrive after such an event so you know we think of mass extinctions and understand it from the through the lens of the individual species but is there some benefit to that kind of a reset uh at a sort of biosphere level well um as people have said in many circumstances when you have a mass extinction there are winners and losers um mass extinction is the removal of of many species and from the perspective of dinosaurs there's not much of an upside to to mass extinction now from the perspective of mammals there's a tremendous upside because mammals had coexisted with dinosaurs for 150 million years and most of the mammals were these little things that lived in trees or in holes in the ground and kept out of the dinosaur's way yeah you removed the dinosaurs and within about 10 million years all of the extent orders of mammals had come into being and it was a very different world i always used to like to talk to my my classes and tell them that you know a clambake during the paleozoic era that is between 541 and 252 million years ago wouldn't have been very satisfying because most of the arthropods are trilobites which have these very small muscle systems and would not give you much of a meal and rather than having clams all over the seafloor you had brachiopods and most of the interior of a brachiopod is simply a filter feeding apparatus there's there's not much brachiopod to it mud right and the reason we don't have that world today was that that world was wiped out by this massive volcanism 252 million years ago and the survivors which preferentially included mollusks and decapod crustaceans uh they then radiated and did a you know a total makeover of marine ecology that brings us closer to today so so yeah mass extinctions are important both for what they remove and for the opportunities they present for those things that happen for one reason or another to to survive oh that yeah that is that is very cool um well you know switching gears though a little bit andy i the other thing that uh of course i love to talk uh with you about is mars uh because you've done such phenomenal work in in helping us understand the martian landscape um and i know this book is about earth's history but you know what what else do you think we can learn about earth's history by studying other other celestial bodies including mars well i think the more we know about other planets in the solar system particularly the inner solar system the more we're able to constrain at least the formative events in in earth history uh you know there is a line of thought you see sometimes it says oh we can learn a lot about the early earth because on earth we literally have no well-preserved rocks older than 4 billion years so the first 500 million years or so of earth history is is a dark age for the most part whereas we have well-preserved sedimentary rocks on mars and while i think that makes it exciting that we can actually look at another planet and do virtual field work on it and learn about that planet's early history i don't know how informative that is for early earth history because you know mars is smaller it's farther from the sun and so while it is true that in the past mars was at least episodically wetter than it is now it's not clear to me that if you went back four billion years that you would see mars really being a mirror of the earth so i think it's really just the the greater context we get for solar system evolution by studying mars and we just learned the other day there's going to be a re-emphasis on venus which is pretty interesting and and i think as much as anything they will help us to understand the uniqueness of earth in the solar system as well as telling us something about how the earth is part of that larger system yeah yeah that really resonates you know and i it's that comparative it's that sort of comparative approach of thinking about not only what we share but but really how we're different than than the other uh planets in our solar system um no thanks for sharing that and um you know i i one more question that i wanted to ask and then i really want to turn it over to our um uh our uh our friends who are on with us here um you know and this one's a bit whimsical so bear with me but um you know there's a very famous broadcaster who of course uh is known for asking someone if they were a tree what kind of tree they would be so i'm going to do something a little similar here andy but if you could go back in time to any period in earth's past and hang around for a year you get one year and don't worry you know you have all the provisions you need you'll have your own little oxygen bubble and all that um when would you go that is to say what time would you visit and why okay that's a good question i i think one of my favorite transitions in our planet's history took place during what's called the ediocarin period which uh goes from about 635 million years ago to 540 million years ago it's bounded on the bottom by a massive ice age and on the top by the radiation of familiar animals including trilobites and things like that and the ediocarin is this time when we see geochemical evidence that oxygen is rising to new levels and the the oceans are getting somewhat more ventilated than they were before we find it's a time of tremendous mountain building in the southern hemisphere we find it's a time of transition in the phosphorus cycle it's starting to look much more modern uh it's the first time when uh primary production by phytoplankton is mostly done by or at least much of it is done by eukaryotic algae rather than photosynthetic bacteria and we start to see macroscopic animals and so all of these major things are happening on the same time frame and i will go to my deathbed convinced that these are all interrelated they are they are not just coincidental events uh but there's still a lot of discussion that that my lab and many others participate in actively and so yeah if i could go back and cheat and really learn what was happening and then write my science paper i could retire happy uh that is outstanding um you know and and um uh you know our friends who have joined us here today have a number of questions uh that they want to run by you so if you'll indulge me here andy let's let's start with brad who has a couple of questions let me just pair these two but brad was curious as to why is the air thinner higher up and brad also wants to know about the last mass extinction and can do can we can we predict when the next one might be okay well i'm going to have to admit ignorance that i i am not a particularly good atmospheric scientist so uh i'm going to have to punt on the question of why uh theirs is thinner than higher up although i'll look it up on wikipedia tonight on extinction unfortunately i think we can predict uh when extinction is going to peak again and it's basically in the time scale of our children and grandchildren's lives as we said earlier we live at a time that is geologically unusual in terms of the rate of change not the magnitude of change that matters it's if change is too fast for populations to either migrate or evolve you know the only other option is to disappear and disappearances tend to be at high rates when the rate of environmental changes is rapid now there's some potential good news in that you know in the past it was bolide impacts or massive volcanism that drove these environmental changes since we're the culprit in this one we have the capacity to actually do what we can to ameliorate the biological consequences of our own activities so with with luck or not with luck actually with very careful planning and discipline and commitment on an international scale we might be able to minimize the amount of extinction that uh that will will happen but that said i i think we are embarking on a time of extinction at rates that have not been seen in many millions of years yeah it is most certainly alarming and i you know i also wanted to you know ask you andy it's um you know is it also you know true that the impacts are going to be felt by humankind as well for the you know i mean i oh yeah yeah so when you know i i think that when we look at mass extinctions it isn't uh we can't just think of it as the loss of a critter here or there but but truly something uh that will change the the shape of our whole biosphere oh oh yeah i mean if if you live in florida and are not concerned about global change it's time to wake up uh you know sea level going up it's already changing uh water availability of aquifers and things like that uh coral reefs that have provided some physical barriers against extreme storms are being influenced very strongly by by global change yeah no there's there is no question that our own lives don't just continue as if nothing is happening because when things are happening all around us we're gonna you know have to have to deal with that i mean all you have to do is ask anyone who's a firefighter in western north america about global change and you know they don't need convincing yeah and you know we're going to see it again this year it's abnormally dry it's warm yep that's what what uh gives rise to major fires so i i think there is are many reasons why all of us should do what we can to leave our children with a saner earth yeah indeed now switching gears a little bit marissa asks what are you most hoping readers will gain uh from this kind of condensed history that you've laid out and and how can we apply that to our understanding of climate change uh as laypersons well that's a good question and i i i wrote it to be honest because um i was concerned that of all the phenomena associated with 21st century environmental change the one that's most concerning i think has been fairly widespread indifference on the part of of populations and so i i wrote the book in the hope that by knowing how the physical and biological earth we see around us came to be will help help us to act wisely when we think about the next chapter which like it or not we are writing so in in a sense then you know the hope is to put 21st century global change in the context of a longer earth history that in fact includes several episodes of rapid global change that in many ways are similar to the one that humans are are uh leading today and i think once we understand that you know just to back off i remember years ago there were all these books like the end of history the end of evolution and they were all nonsense because the plain fact is that you know evolution is not ending in the age of humans humans are simply becoming important evolutionary art arbitrators uh environmental change is not ending in the age of humans in fact it's it's actually ratcheting up to geologically unusual rates so uh again in some ways the hope is that people will understand how and to what extent humans have become a potent geologic force and be able to appreciate that in the context of our planet's history as a whole yeah absolutely um yeah thanks for that andy uh now yvonne asks uh or says states and then asks you you've underscored through your great research the connection between geology and biology how do we consider in the present time the impact of human-made substances toxic synthetics and similar factors with respect to evolution and or survival that's that's a great question uh one factoid that i actually use in the book because i was bowled over when i i first heard it at a meeting a few years ago is the uh estimate that uh there's basically a garbage truck's worth of plastic dumped into the ocean every hour something like this and i think there's no question that among the important things that we are doing that have an impact on both the physical environment and species does occur through those substances that are that are man-made so certainly plastics are a very important source of pollution both on land and in the oceans there are a number of uh chemicals that and we're always finding out new ones that have been uh are toxic to species um so yeah in fact and it isn't even just the things that that are toxic one of the things that humans do for for reasonable reasons is we put fertilizers on fields because we want to increase the yields of crops and that that makes perfect sense but you know of all the sort of phosphorus and nitrate that gets dumped onto the fields in the midwestern united states only about a third of that gets used by those plants most of it gets rained out goes into the rivers ends up in the gulf of mexico and then it actually contributes to growth but it's the growth of algae it makes these big blooms which then settle down and the respiration of that organic matter leads to um you know what are called dead zones and that that's a name that pretty much is self-explanatory and the dead zone in the gulf of mexico was you know about what 10 square kilometers the first year it was found now every year it's about the size of new jersey so you know everything we do because there are so many of us has uh an impact on the natural world that we have to take into account and and and be careful about yeah yeah and i want to you know i i for one caught my attention is that that that you said every year you know we so often think of these fertilizer runoffs or these other things this may be a an episodic event once every once in a while we do something bad but this is now predictable and growing and problematic um and it's of course for for the organisms that live there but also for for um for humankind's dependence on the ocean you know the the those dead zones have killed off a lot of fisheries and the like it's yeah and they're all over the world i mean it's sort of i i don't i just pick on uh on the gulf of mexico there are now dozens if not hundreds of these and they have similar consequences wherever they're found and those certainly include uh fisheries and hatcheries that have strong human consequences absolutely well these folk we got questions rolling in from folks so here's here's one um while the extinction of dinosaurs uh takes precedent in most people's minds when thinking of you know massive geological change what other key elements in earth's development professor noel do you wish were more widely known and taught oh that's a good question yeah i mean all of us who are paleontologists live in the shadow of dinosaurs and we just have to get used to it and get on with life on the other hand you know dinosaurs were massive they you know keep you awake at night but they fundamentally didn't change the earth whereas cyanobacteria who i think are they're my favorite organisms these are the bacteria the one group of bacteria that evolve the ability to do what we call green plant photosynthesis which involves taking water breaking it down to get electrons from it and giving off oxygen gas as a as a byproduct now i should say inter alia that it's wrong to call that green plant photosynthesis because the reason that plants can do photosynthesis is that one of their ancestors captured a cyanobacterium and reduced it to metabolic slavery so the the chloroplasts in plants are genealogically cyanobacteria and those organisms fundamentally changed the world you know for the first two billion years of our planet's history there was no large or long-term accumulation of oxygen in the atmosphere and surface ocean and the reason it happened again it required a biological innovation which was cyanobacterial photosynthesis but it also required changes in the earth so that's a an event where earth and life are working in tandem just changing the planet fundamentally and and so i i would just say yes i i think dinosaurs are are great uh maybe in retirement i'll i'll get some of my buddies to take me out and do field work on them but i think there are all these great moments in earth history and that's what i've actually tried to organize the book around that you know the origin of the earth original life oxygen animals things getting on continents the greening of the earth and catastrophic earth the mass extinctions and then finally us who are probably as important as any group of organisms since the cyanobacteria yeah yeah it is very cool i mean as a fellow microbial aficionado i've got my vote um now peter asks um and let's let's maybe professor noel you take your sort of best guess at this at the current rate of human co2 emissions how long do you think it might take to reach the co2 amounts comparable to the end permian extinction oh that's a good question and in a very odd way there might be good news there um people have actually suggested that the the rate of increase that is you know how much additional co2 is added to the atmosphere every year might be greater today than it was at the end of the permian period but that's because the volcanism goes on for many thousands of years no matter what we do uh we will not have thousands of years of uh increase in co2 simply because we'll run out of fossil fuels so i i think i'm more worried about how much things will change in the next 50 years or so when we will certainly go over 500 parts per million co2 and possibly a good deal higher but i think in some ways the good news is that many people around the world are now really putting new vigorous exciting energy into uh renewable of fuel sources and and that and and i think that i mean if you have stock in a petroleum company you better hope that petroleum company is investing in uh in uh renewables because you know even with the most optimistic projections for reservoirs that are yet to be depleted you know we're talking about a world where petroleum does not play an important role i think by the time we get to the end of this century if not before yep yep so now victor asks a question that i think will appeal to you here how did animal size change over evolutionary time and is it possible to trace size for an evolutionarily lineage for example if you look at the lineage of humans how far back in time does average individual size sort of change it can be estimated yeah we can and that's that's the beauty of the fossil record that that it uh preserves uh morphology and actually i'll put in a plug for a former student of mine john payne who teaches at stanford and john and his students have actually done a lot of this work and so for example on the longest time scales we see that the the first animals that we can look at and say oh that's an arthropod or that's a mollusk or that's a that's a brachiopod in the cambrian period are relatively small and they get larger as time goes on if you look at uh marine vertebrates many of which have come back into the marine realm from terrestrial ancestors they get larger through time over the last 200 million years certainly humans are the human lineage called hominins have gotten larger going from australopithecines a couple million years ago that were maybe a meter or so tall to uh you know modern humans some somewhat larger than that so yes there have been a number of uh good papers on this size does change through time uh we tend to look at increases in size but there are times when that reverses so for example if you look just after the big mass extinction 252 million years ago almost all the survivors are really small there was something about being small that facilitated survival and then over millions of years uh not everything and again it's it's an increase in the variance that is we still have lots of small animals today but some of them get get larger and larger so there there's a rich record there and we can look at it for animals writ large we can look at it for individual taxes through time that's very cool you know now susan asks a question um and she writes what steps are necessary to inform the general public about well about your subject about these ideas so that we can all take the necessary steps to respect our planet and maybe we can rephrase that as a you know what tips do you have for us andy as we as we inform uh our our friends and and colleagues um so that we can all move towards uh being more mindful of of how we treat our environment yeah that's a an important question and uh my approach to an answer actually comes from a rather remarkable statement made by a senegalese forest ranger named baba dayum years ago when he was asked about public support for conservation and his answer was i think just memorable he said we will conserve only what we love we will love only what we understand and we will understand only what we're taught so i i think that in the first instance we really want to be effective in schools in churches in civic associations in just trying to educate people to both the past present and and future of our own planet because i think people who don't have any understanding of how our planet works and our dependence on that working are unlikely to see why they should change their ways and you know as i said earlier i think that's really one of the primary motivations i had in writing this little book i guess to get something that hopefully almost everybody can read and maybe learn well yeah i that that was a a real wonderful perspective andy and um i'll just say that if i can read this book with three boys jumping on my head uh anybody can read this book i really it's it really is a wonderful read folks so do share it with your friends and i do think it's books like this and and and uh events like like this one andy that give us a chance to share with others uh you know what you've learned uh and and promote those conversations in in our different you know little corners of the world right um now a couple more questions as we're kind of uh moving towards the end of our time together here um steven asks uh his understanding is that there's a layer of iridium and sedimentary rocks roughly going back 65 million years ago and bolstering the evidence of an impact um steven wants to know what will future intelligent species sorry stephen i'll i'll say perhaps more intelligent species what will they find about in rocks from humans from today yeah that that's a great question and there's actually been a fair amount of work on it for a a very interesting reason and that is as many people who are part of this conversation will know we divide geologic history up into time intervals periods the cambrian the ordovician etc and we subdivide those into ethics and there has been growing interest in recognizing the age of human hegemony as the anthropocene and that has led to a lot of interesting discussion and work on you know if you look in the rock record where do we start seeing evidence of humans and and again it turns out that everything didn't you know human influence didn't start in 1945. uh you can go back well over 10 000 years and see influence of humans burning for example on vegetation and that but there's no question that beginning with the industrial age and actually accelerating since world war ii i think it's fair to say that most of the fossil fuels ever burned in the history of humans have been burned since world war ii uh we do begin to see records well we we see records of atomic bomb tests we see records of plastics i remember reading a paper about how there was this line and i think the gulf of california above which you found beer cans and you didn't find them below so i i think there's no question that a a geologist or paleontologist looking back at today from 10 million years from now would see a diminution in biological diversity and it would be at the same time as we would see this big increase in human generated products that are ending the geologic record and i and i think that would lead to uh probably rapid consensus that uh technological humans were responsible for that diminution and diversity oh that's very cool now one last question as briefly as we can in the time we have but a fun one to end on um one of our uh anonymous friends here asks can you give us some of your thoughts on how changes in elemental availability or geological factors in other words the physical environment may have affected affected cognitive evolution what do you think that's that's a good question um i was all ready to give an answer because i think on on longer time scales of earth history there's no question that for example i i think the story of oxygen is basically the story of phosphorous availability over over 4 billion years cognitive evolution is a a little bit harder and there's one of the questions is when do we start seeing evidence of humans that that think the way we do and here i'll give a plug to uh someone who's just down the hall from me dan lieberman in human evolutionary biology who says you know we don't know quite what it is but you know 40 000 years ago humans started acting differently and we do see cave paintings now in indonesia that go back to 45 000 years that tell us something about spirituality as well as cognition somewhere on that time scale very hard to trace through the geologic record language is becoming important uh new technical technologies tool cultures and that are coming in so there's something that's happening at that time interval and and to be honest it isn't clear to me that there's any change being imposed by the physical world on on that it may be something that simply reflects the you know the tremendous fitness advantage of being able to communicate work together and do all those things that we take for granted in human society yeah that is a a wonderful note to end on and end on and here's hoping that we can put this cognition to good use first check out the book it is really a delightful read and secondly let's uh hope that we can uh you know share what we've learned not just here but broadly about uh our relationship with this world both the abiotic and biotic and really try and uh do right by this planet and make it a better place but but andy i want to thank you so much this has been a real blast and thank you folks uh who joined us and for the for the many wonderful questions uh lauren i'll pass it back to you thanks peter thank you so much thank you peter for that wonderful moderation and thank you andrew for sharing this book with us um this is a really fantastic conversation um please do check out a brief history of earth on harvard.com and on behalf of the harvard division of science the harvard library and the harvard bookstore all here in cambridge massachusetts um have a great evening keep reading and stay cool and be well thank you so much guys hi thanks everyone we'll catch you later
2021-09-11