Andrew Knoll, "A Brief History of Earth: Four Billion Years in Eight Chapters," with Peter Girguis

Andrew Knoll,

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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 22:31

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