EGU GIFT2018: The great oxidation event, 2.3 billion years ago

so thank you it's a honor to be invited to give this presentation and tell you what we don't know a little bit about what we know about the great oxidation event one of the great transformations maybe after the origin of life the greatest transformation in the history of life on Earth just to orient you a little bit to what the what it is we're trying to understand this is a quick cartoon showing you the relative abundances of the gases in the atmosphere most of the earth's atmosphere is nitrogen but the next most abundant gas is oxygen at about 21% today so the question is how'd it get to be that way wasn't always 21% and it's rather important it's 21% because we wouldn't be here otherwise to enjoy this enjoy this conference and enjoy everything so this is this is a first order challenge in Earth history trying to understand how the atmosphere got to be the way it is the answer to that we don't fully understand but we know that the way we get to it is through the rocks I think was Carl yesterday showed a picture of a banded iron formation so this is a spectacular setting in Western Australia where you can see these banded iron formations these are rocks that appear uniquely towards the middle part of Earth's history then they go away and we essentially never see rocks like this in the geologic record afterwards and we think this has to do with the rise of oxygen I show you this particular as a website this particular picture the website because this is a teaching resource here that I think might be useful to some of you that a group that I lead at Arizona State University this Center for education through exploration produces we produce a virtual field trips among other things we produce immersive interactive virtual field trips that take you to places where your students unfortunately well and most of us will never get to go but we've gotten to go to some of these places and capture some pretty exciting renderings and imagery and and data for these places and have these as resources that you and your students can go visit and in some cases we've built interactive and adaptive lessons that take students through these locations and teach particular scientific concepts so that's the there's a link to this in the brochure and in the pack in the packet if you go to my page they there's some links and one of them is 2vf t dot asu.edu which is a website that has dozens of these virtual field trips and growing a little bit every year so what we want to understand in this particular case is the origin the cause of the great oxidation events this is a plot showing you oxygen through time so here's four and a half billion years ago here's today and this is summary from a few years ago of oxygen in the atmosphere over time so here we are today at around 20% oxygen in the atmosphere here's the first half of history with very little or no oxygen and then there's this sharp change that happens around 2.3 billion years ago we argue about the exact date roughly halfway through Earth history we have this sharp increase that we refer to as the great oxidation event so this is what we want to we like to understand why this happened big transition in the history of the planet not the only transition involving oxygen and a worth noting that this is if you're teaching a math class this is worth pointing out this is a log plot here that axis here is law a logarithmic and on a log plot this looks like the big increase but if you were to plot this as linear plot this would be the big increase right so sometimes you know when you switch from linear to log things can look quite different so so there's a second big increase here in the neoproterozoic the neoproterozoic oxygenate oxidation event and this really made the rise of animals possible but this rides wouldn't have happened if this rides hadn't happened first so we refer to this one as the the great oxidation event even though an actual amount of oxygen it's smaller because here we went from almost nothing to something that we argue about how much but something appreciable so before we launch into what happened it's and why maybe we should talk a little about why we care certainly in education that's something your students will ask you about I get asked all the time not just by students but why why do we care about this and I'm gonna give you two reasons that both come from this orientation of about thinking about the earth as a planet this is a pic this is a pale blue dot this is Earth you're all in this picture all of us are in this picture few years ago it was taken this is from the Cassini orbiter when it was orbiting Saturn and they pointed it back to earth to take a family portrait about all of us so here's earth as a planet and when you think about Earth as a planet there are two big air is that pop into our minds many of us who are geosciences one is to think about life on other planets and how we would look for it how would we look for life on this planet from a distance like this so the astrobiology questions that motivate many people and the other questions that motivate many people when you're geoscientists or just a citizen of the planet and occupant of the planet thing about the future our Anthropocene questions about the future of this world and in both cases the oxygen question has some some very big picture relevance so from the astrobiology standpoint as most of you probably are aware we're discovering planets outside our solar system at a crazy crazy pace there are now over 3000 over 3500 confirmed planets orbiting other stars so 2530 years ago now as a graduate student it was science fiction's even you consider kind of crazy to try to go into that field of science and now it's almost boring it's like easy to find planets that's kind of amazing when you think about it almost a thousand of the planets that have been found are terrestrial planets meaning they're rocky planets they aren't quite necessarily earth size and most immersed super Earths but these are planets where we can start thinking about life like hours on and and and this is growing all the time every time I give a version this talk I go to the JPL website and update these numbers because they change weekly so we're finding exoplanets all over the place this is the Kepler space telescope which is one of the main ways we've found a lot of these planets and it finds planets by looking at dips in the brightness of light from the star as a planet passes in front of the star and that sets up the ability to do once we get better telescopes spectroscopy you can imagine if you have a planet passing between us and a star that the lights that's going through the atmosphere of that planet will be dimmed differently will absorb certain wavelengths of light due to the gases in the atmosphere you can do spectroscopy and tell what the atmosphere is made of we can only do that now for terrestrial planets orbiting other stars but we will be able to it's a big goal that NASA and ESA have the so-called spectroscopic search for biosignatures and oxygen looms very large among the ways we might do this so here look at our solar system as an example here's Venus Earth and Mars and if we look at the infrared wavelengths we see that the atoms Venus has this big feature due to the absorption of carbon dioxide there's a the Venus atmosphere is about 90 times Earth's atmosphere and pressure and it's almost all carbon dioxide and carbon dioxide is a very strong infrared absorbers there's a very strong infrared feature and not much else Mars Mars has almost no atmosphere it's an atmosphere of six millibars of pressure it's it's it's six thousandth of the Earth's atmosphere but it's also almost entirely co2 so there's this big absorption feature due to co2 and there's really nothing else if you make the same kind of observation of Earth in the infrared you again see SCO to feature the earth has 400 ppm co2 and rising but you also see this interesting feature here from ozone in the Earth's atmosphere you don't see this in the Venus or the Venus or Mars atmospheres an ozone is a byproduct of having a large amount of oxygen in the atmosphere and so this is arguably diagnostic of life the spectroscopy of Earth's atmosphere looks different in the spectroscopy of the atmospheres of Venus and Mars because Earth has life which pumps out oxygen through photosynthesis and and gives us this this feature so this is one of the sorts of data that astronomers want to obtain from planets orbiting other stars or to look for right now if we found something like this we'd get very excited and then we'd argue about whether or not they're non-biological is to make ways to make that and we'd have you know twenty more years of controversy but at least we'd have we'd move the ball down the court in terms of what we're arguing about so oxygen looms large in this astrobiology field and so wanting to understand it's kind of important than understand what controls oxygen in the app in the atmosphere from the Anthropocene perspective you know we're entering this epoch of Earth history where the future the planet is very much in the hands of us of beings walking around with big brains and hands who are big evolutionary innovation on this world perhaps as big an evolutionary innovation as the right as the photosynthesizers that evolved we'll talk about when they evolved and changed the surface of the planet so the earth is very much in our hands and that's leading to all sorts of amazing and scary ideas like deliberate intervention in the Earth's climate system as a way of coping with what we've been doing accidentally to the Earth's climate system so ideas of deliberately removing co2 from the atmosphere sort of cleaning up our wastes or deliberately modifying the Earth's atmosphere to reflect sunlight these are ideas that are being taken very very seriously in the most by the most of Guus scientific bodies and natural National Research Council of the u.s. issued a report on this a few years ago working on another one now so there are ideas like this that are out there as we enter this sort of hopefully adulthood at least teenager hood of humanity on the planet and their ideas like this they're floating around Elon Musk wants to terraform Mars now we're a long way from doing this but this is the kind of this kind of talk is out there and it's going beyond science fiction into people who actually have industrial capacity to try to do things this is where Elon Musk is aiming he wants to make Mars green okay if we're gonna start modifying the earth let alone modifying other planets if this isn't something really gonna think about we kind of need to understand the system that we're modifying and if we don't understand why the earth has 20% oxygen the atmosphere and how it got to be that way which is one of the first-order things you could ask about in our atmosphere then I think you could rightly say that our knowledge is pretty primitive compared to our ambitions and our abilities and this is something we might want to try to understand if you want understand your system one of the first-order things you might want to be able to be able to explain is when did the Earth's atmosphere become 20% and why did that happen in oxygen it's like a first-order feature of the atmosphere if you can't explain that one you know we're in bad shape trying to do anything deliberate to earth let alone try to replicate earth somewhere else so so for both these reasons but the astrobiological and the anthropocentric reasons this oxygen pursuits is a very big picture important thing to try to figure out so so what caused the great oxidation event and I'm just noticing that the timer didn't start so I have no idea if I'm on pace or not just so Carl oh please or max back oh yeah I know I'm okay right now but later on let me know so what caused the great oxidation event how do we get oxygen in the air in the atmosphere so there's one process that nobody talks about very much but is worth worth noting so that you're aware of there's a continual source of oxygen to the Earth's atmosphere from the loss of hydrogen at the top of the atmosphere this is a process that happens all the time it's happened throughout Earth history it's happening right now we can actually see emission of photons from in this process hydrogen being lost at the top of the atmosphere we've heard a little about it yesterday from John's heart do you know in the context of the Martian atmosphere a massive atmospheric loss happens on earth - for hydrogen and if you lose hydrogen you leave behind oxygen most that hydrogen is coming one way or another it was kind of paired with with what oxygen and water at one point and as you lose hydrogen you gradually oxidize the planet so there's a continual geophysical source of oxygen over time and people argue about its magnitude and it certainly plays a role but there's no reason to think there was some big inflection or anything like that some big change halfway through with history and the rate of hydrogen loss so we don't think this is the story about the great oxidation and we don't think this is this is it but it's a factor that needs to be thought about and considered the textbooks will say something like this especially the biology textbooks will say something like this the rise of oxygen is due to the evolution of photosynthesis life figured out how to take co2 and water and react them to make oxygen and organic carbon this is the geochemists way of writing organic carbon we don't actually mean the molecule C h2o we mean this estoy qiyamah tree one carbon to two hydrogen's to one oxygen in a whole array of different molecules my chemistry friends especially my biochemistry friends are horrified whenever I write this equation down but stoichiometrically it makes sense one co2 to one water - makes one oxygen and an organic carbon molecule so that the biology textbooks will tell you well this evolved and oxygen rose and a story we can we can drop the mic and go out right that's the end of the end of the game but the geologists if you look at the geology it's more complicated than that and since we're here at a gift workshop not a gift workshop it's a gift workshop we're going to delve a little into the geology so this is a virtual field trip to Shark Bay in Western Australia to karbala Beach specifically and this looks kind of nice and pretty but kind of nondescript until you go under the water when you see these mound like things all around you and if you and these are really interesting to swim around with it's kind of cold also - but once you get over the shock of how cold it is there really interests come around and if you look at these things very closely what you find is that while they look like rocks they're really not or they're not purely rocks there are layers of microbial microbes and and sediment interbedded and the microbes are living here are dominantly cyanobacteria and there's cyanobacteria that are making oxygen and we call these things when their fossilized we call them stromatolites these are modern versions of what we find in the ancient fossil record that are called stromatolites and they are these very complex microbial communities that leave behind a very distinct geological marker in the form of these things which when they get buried and lithified they're pretty distinctive in in ancient rocks so when we go back in the geologic record what we find is that before the rise of animals you go back before a half a billion years ago or so you find the fossil remains of stromatolites are quite common you find them even if you go back before the great oxidation event 2.7 billion years ago this is in Western Australia go up this Ridge here I don't know if the lighting works well if you can see this all that well but but we'll zoom in to this cross-section and you can find these fossilized from a delights that are we're gonna zoom in over here that are absolutely spectacular and you can again feel lighting a little better you could see all the glorious detail in here and I'm not a paleontologist let alone a geo microbiologist but those who are look at these and say oh yeah we can we can pretty convincingly argue that these are fossilized forms of those stromatolite s-- that we were swimming amongst in Shark Bay that you can find living today and when you go back into the the Precambrian before the the rise of animals this is the dominant form of life that you see in terms of anything macroscopic that you can see that's biological today these terminal i'ts that we see today make oxygen and so it's quite conceivable that these are making oxygen as well and notice the date here this is 2.7 million years ago the great oxidation is 2.3 billion years ago so we're already quite a bit of time before the great oxidation event here and we see these stromatolites we can go to some of the oldest sediments that we that we know of oldest nicely preserved sedimentary rocks these are the these are rocks in the dresser formation 3.5 billion years ago in Western Australia and they aren't nearly as well-preserved but they are not terrible and you can make an argument that in some of these rocks we see structures features that are that have been interpreted again as being mr. Matt lights at 3.5 billion years ago and if you look at the detailed morphology of these of these stromatolites the argument has been made that that indeed they were oxygen producing stromatolites now that's not a slam dunk that's very contentious but you can at least make the case and it's not a weak case that there could have been oxygen production as early as 3.5 billion years ago just based on the fossil record so the great oxidation event happens in about 2.3 billion years ago but well before that there's there was certainly biology there was certainly phototactic biology those making use of sunlight and there's a good case to make any way that that biology was making oxygen so it's not as simple as saying oh photosynthesis turns on and oxygen takes over the world now we being geochemists we don't believe all that morphological fossil stuff some of us well so that we don't believe it it's that we we we trust magical things that emerge from our mass spectrometers more so so we work with our paleontological partners to do things that are geochemical to try to confirm verify and extend what what the paleontologists find the paleo biologists find so what I'm gonna walk you through here now is a little bit of stuff that my group and collaborators have done looking at of all things the element molybdenum why molybdenum of any you read the Hitchhiker's Guide to the galaxy in this room Hitchhiker's Guide to the galaxy ever read that yeah what's the answer to life the universe and everything 42 it's element 42 so of course you'd be usable of did and what else would you do but that's not the real reason using Libman the reason we look at molybdenum in ancient rocks is because it turns out the geochemistry of molybdenum in the environment is very sensitive to the amount of oxygen that's around it's a proxy for oxygen the amount of molybdenum in certain kinds of sediments as a proxy for the amount of oxygen in the environment we can't record ancient oxygen directly in rocks billions of years ago but we can reconstruct him out of molybdenum that was in rocks laid down billions of years ago and from that infer what the chemistry of the atmosphere notions was or draw some inferences and libel is not the only element but it's probably when it's been looked at the most carefully in this regard so there's a number of of molybdenum related arguments I could make to you but this is probably the simplest one to get across in the short talk so molybdenum in in in crustal rocks especially in igneous rocks which are the primary rocks of the make up the crust molybdenum is found inside sulphide minerals dominantly sometimes as an impurity in pyrite and sometimes as molybdenum sulfide molybdenite is a sulfide mineral that is a molybdenum bearing mineral but either way those sulfide minerals are major reservoirs of molybdenum in the crust and they react quite vigorously with o2 right sulfide minerals oxidize quite readily if you expose them to oxygen they don't really fall apart right away sitting on your desk but give it a logical time and you know your fool's gold your iron pyrite sitting on your desk is not gonna last all that long because it's reacting with the oxygen in the atmosphere so the logic of using molybdenum is a paleo redox proxy goes something like this imagine I've got a continental crust that has molybdenite molybdenum in sulfide minerals in it if there's no oxygen in the environment if oxygen is absent then that molybdenum basically stays locked in the sulfides and if it stays locked the sulfides there's really not much opportunity for molybdenum to get into the oceans and so the molybdenum concentration the oceans is low and if you go to ocean sediments that could scavenge molybdenum if it was there you'll find that there isn't much gold in them there but if I turn oxygen on if there's oxygen around in the environment then these sulfides oxidize they fall apart they deliver their sulfur their molybdenum into the oceans and the molybdenum content of the oceans Rises and I can find evidence of that in the geologic record that's the that's the the simple logic and we can make it more complicated with equations in math and talk about solubilities and stuff like that but the logic is basically this all right so no oxygen molybdenum stays locked up in the crust oxygen around one of them can accumulate in seawater and all the rest is important comment so we can go into ocean sediments that are ancient we look at the kind of sediments in which molybdenum can accumulate if it's in the water in the first place not all sediments will scavenge molybdenum for example calcium carbonate rocks are very molybdenum poor molybdenum really go into calcium carbonate very well but malignant goes very nicely into black shales into carbon rich organic carbon rich rocks that make that sediments that eventually make up these kind of sedimentary rocks called black shales and so there's a small cottage industry of us going around drilling ancient sedimentary sequences to get these nice black shales out that are well preserved and then measure the heck out of them for molybdenum and other trace elements and isotopes to try to reconstruct what the chemistry of the waters was waters were where these sediments were accumulating billions of years ago and when we've done that we've been able to do things like this so here we're looking through time here's today here's three billion years ago so we're not going all the way back here yet so zero to three billion years here's a molybdenum concentration in black shales so it's been done here is to get black shales through time measure the molybdenum contents and then plot them up and what you can see is in the last half billion years or so the molybdenum contents are quite high which makes sense because the last half billion years or so there's been a lot of oxygen in the environment ten twenty percent oxygen a little image should be a very mobile element in that world it should be abundant in seawater like it is today today one of them is the most abundant transition metal and seawater it's still very scarce but it's but it's but compared to other metals it's quite abundant in seawater and that was probably true for most of the last half billion years or so and that's why you see good enrichments all the way up here then you go earlier remember I've mentioned that that neoproterozoic oxidation event so we go before that time and melittin concentrations are lower and then we go further back and there's not a lot of data and the concentrations are lower still so you have this sort of first order confirmation of this kind of threefold or two step change low something goes up and then it goes up again kind of like what I showed you before for oxygen and this is this is this is one line of evidence that's taken to say taken as support for that hypothesis I gave you they we can use molybdenum as a way of tracing oxygen through time but let's dig into this a little bit more so that great oxidation event happens at about 2.3 billion years ago that's right around here here's 2.5 billion years ago and you can see that is actually somewhat it's actually not there's not a big difference here there's not a big step here hmm what's going on here so let's look at this more closely so this is a this is data that that my group and collaborators generated about 10 years ago at this point we wanted to look at sorry at whoops back at that point of time we didn't have these data that was just very low we said let's start looking before the great oxidation event and see is there molybdenum around in environment and what we found is in these rocks from about 2.5 billion years ago with is these beautifully preserved black shales when we looked with depth in these rocks we found this enrichment of molybdenum it's kind of transient but as an enrichment of molybdenum that goes up to around 40 parts per million at around 2.5 billion years ago this is a healthy amount of molybdenum and you can look at other tracers we won't go into all this because it gets to all sorts of geochemical nerd nerdiness that we don't need to go into don't have time for but all sorts of things kick here at the same time and you can argue about alteration and stuff like that but but we and most people are pretty convinced at this point this is all primary it's all telling you something about the original seawater and what we think we see here is a transient pulse of molybdenum in the environment and we've argued that that actually reflects a transient whiff of oxygen small amounts of oxygen wafting into the environment in sort of variable ways a bit like today right today methane is a rare gas the atmosphere but but it's around that it varies in concentration certainly over over tens and hundreds and thousands of years it can vary up and down and so we would argue that in this pre great oxidation event environment we had oxygen as a minor gas but one that varied around and sometimes you might get a pulse of it for a few million years depending on vagaries of biological production and other things that are going on so we call this the whiff of oxygen and the picture that emerges from this in other studies is that during that first half of history whereas today the it's quite simple more or less oxygen penetrates through the water column in places most parts of the world the environment is the oceans are thoroughly oxygenated we think that before the great oxidation event it was a more complicated picture we had large volumes of ocean water that our so called ferruginous they had very little oxygen but lots of iron that's why you could get those banded iron formations and then as you went to nearshore environment you had we argued and this is not just us as a classic argument actually you had cyanobacteria living close to the seashore producing oxygen creating an oxidized near-surface region and sort of oxygen Oasis so some regions Laura large but contained regions that were oxygenated in the shallow waters overlying and paradoxical reasons we could talk about later on you get these very reducing sulphide rich regions below that but the basic story here is a kind of heterogeneous story with some oxygen around in these nearshore environments probably being produced by cyanobacteria probably many of them in communities like those stromatolite s-- so we see fossil record of stromatolites and we see geochemical evidence that we argue as evidence of their being oxygen around in the environments in small amounts before the great oxidation event so again the geochemistry is telling us something similar to the fossil evidence which is that it's not as simple as life figures out how to make oxygen and boom a way it goes we had a long period of time it looks like when life was around possibly making oxygen but the but the environment was not taking off into a 20% or anything close to that oxygen in the rich atmosphere right so here's this taking this diagram again from my friend Tim Lyons and adding into it oxygen etic photosynthesis we think oxygen in photosynthesis is old I think today we might extend this back to 3.5 based on some other data that that's out there now but the rise of oxygen was delayed and didn't happen until around 2.3 billion years ago so in text summary so far before we get to the conclusion here how am i doing on time ten more minutes perfect so summary so far the great oxidation event occurred around 2.3 billion years ago we kind of took that as a given I didn't show you the evidence for that but just take that as a given evidence of microbial matze which when fossilized stromatolites The MITRE produce oxygen or found as far back as 3.5 billion years ago molybdenum and other elements in ancient ocean sediments suggest a slightly oxidizing surface environment and hence arguably and this is all arguable but arguably oxygen production at least by two and a half billion years ago and I didn't show you this evidence but but there's other things they're a little more complicated show around molybdenum a little you isotopes and chromium isotopes and stuff like that all of which lets you extend this kind of argument back to almost 3.5 billion years ago this is geochemical evidence and so yes photosynthesis was necessary for the great oxygen to oxidation event we don't think you can get a 20% or even close to an oxygen atmosphere on earth without having biology pumping oxygen in the environment but it originated much earlier another way putting this does photosynthesis is a necessary condition but it's not sufficient on its own to explain why we wind up with a heavily oxygen atmosphere so this question what caused the great oxidation event we can be a little more sophisticated about it now the question we really need to be asking is not what caused the event but what kept oxygen low before the great oxidation event it was being produced we think but something was keeping it down so there's a broadly two arguments that people make and one that I'll argue is is more likely or to be more important that to try to account for this so we need to get into one more step of geochemistry to to understand the first these arguments so we talked about oxygen the atmosphere but it turns out that oxygen in the atmosphere the accumulation of oxygen the atmosphere is a consequence of burial of organic carbon how's that work so it's a very simple way to sort of conceptualize this so this is such a tight relationship that in the literature you'll find people talking about organic carbon burial as if it's synonymous with oxygen production and unless you know what's going on it's like why they talk about organic carbon burial we're talking again probably or what is this so I want to get this across to you here so co2 and water are the reactants in photosynthesis in oxygen producing photosynthesis so they react to make oxygen and organic carbon that's the photosynthetic reaction but as you all know unconsciously if not consciously because you're doing this right now with your breakfast the back reaction of aerobic respiration takes oxygen and organic carbon and turns it back into co2 and water we're all doing this right now as we speak and on a global basis these are pretty finely balanced actually pretty much all the organic carbon and oxygen that are produced every year by biology our Rican soom by respiration I mean why wouldn't be that way they're all organic carbons they're docked in the atmosphere so if if if this is being made there are bacteria and other organisms that are gonna do this back reaction and respire it so how do you actually then accumulate any oxygen in the environment at all how do you end up building up oxygen in the atmosphere what happens that there's a trickle of organic carbon that gets buried in sediments on geologic timescales and gets protected for for hundreds of millions or billions of years from reoxidation and for every mole of organic carbon that you bury you leave behind a mole of oxygen in the atmosphere so there's a so barrel and sediments this is geology now right so everything here is biology but this is geology and so if you do things that change the efficiency with which you can bury organic carbon in sediments over time you can change the source the effective source of oxygen in the atmosphere so one classic argument that has been made is that the rate of burial of organic carbon in sediments might have changed are there because of geological changes or maybe because of changes in evolution that changed the efficiency with which organic carbon gets packaged and sent into sediments and so perhaps early on Earth history we were simply burying less organic carbon than we are today and maybe that maybe there was a big change that caused the great oxidation event so this gets too complicated to go into I just want to summarize the result people have looked at this hard they've used carbon isotopes and this is a whole hour long lecture to explain how you use carbon isotopes to get at this but they've tried to reconstruct the fraction of carbon in the surface environment that gets buried as organic carbon through time here's 3.5 billion years ago here's today and there is indeed a bit of a trend we are bearing a bit more organic carbon today than we used to but and and this is an attempt this is this study by Kristensen Totten is an attempt to really put rigorous statistics on this and the statistics tell you that yes there is a change here but it's not enough to account for the great oxidation event so there has been an increase in the barrel of organic carbon which means there is an increase in the effective source Vox from the environment but it's not enough to explain this big change that we see 2.3 billion years ago so we need to look for other things instead or in addition and so here again we come to geology what about the geological sinks for oxygen so over geologic time we produce oxygen through burial of organic carbon which leaves Auction behind and we also have escape of hydrogen space which is a source of oxygen I talked about the beginning but what happens to that oxygen that gets accumulated in the atmosphere well it reacts with things it reacts with reduced minerals on the continents through enduring weathering it reacts with volcanic gases and with rocks on the seafloor it reacts with volcanic gases on land and with metamorphic gases these are all sinks ways of consuming oxygen and so the question that has loomed large and last 10 15 years is well can we get better understand all these sinks and how do they change and if you think about it the Earth's interior is a very chemically reducing place it's effectively an infinite sink for oxygen and most of the planet is the interior right the oxygen that we talking about the atmosphere is very thin scum here it's a tiny tiny tiny fraction of the mass of the planet and so changes even small changes in the interaction between the Interior and the surface could make a big difference in the oxygen sink strength on the surface so you could have things the most controversially what if the actual redox state of the mantle changed slightly and Steve's talk would you summarize when he summarized avoiders work he talked about possible changes in the oxygen fugacity of the mantle that's a way of talking about how reducing the mantle is has this changed over time in some ways has the composition the continental crust changes changed in ways that would change the sync strength of oxygen and what about the composition and flux of volcanic gases means here or how is have those things changed so all these things have become areas of serious investigation over the last decade or so and it turns out there's support for each of these ideas against our it's argued about but but there's a blizzard of papers and this is only some of them there's more where people have attacked various ideas like this and shown hey this could be true this could be true this could be true and we're only now getting into the end of the stage where people are starting to attack some of these papers and see which ones can be shot down this is an area of very have a lot of intellectual ferment right now of looking at these geological sinks and try understand which ones are important and which ones aren't and what I'd like to leave you with is the thought that perhaps they're all important perhaps these are all just different parts of the elephant that we're all feeling in our blindness and imagine this kind of thought experiment imagine we begin with a hot earth an earth where there's where there's a very rapid exchange between the surface of the Interior because it's hot and it's it's in motion the mantle is convecting faster and things like that and so you have a lot of interaction between whatever oxygen is produced here and they reduced interior and so oxygen can never really rise can't really take off because you have to rapid interaction with the surface and interior and then as the planet cools down you kind of slowly freeze that out right you slow down the interactions between the surfaces interior and oxygen can increase and perhaps all these things we're talking about change in crustal composition changing the amount of the cross changeable can of gases all those really are symptoms changes in those things are is going to be symptoms of cooling of the planet so maybe what we really need to do if you really want to nail this question this topic is to sort of develop a theory of the earth there's been some previous attempts to write books called theory of the earth perhaps what we need to do as a community try to put together a theory of the earth system that really integrates that well the story that's emerged in the surface and what we're starting to figure out about the deep interior and its interaction with the surface and we really need to sit down as communities together and try to figure this out it turns out the surface earth scientists and deep earth scientists don't tend to talk to each other all that much don't tend to do research all that they don't even understand each other's questions and problems and vocabulary at the time all that much but maybe it's time we need to pull that together in order to resolve this problem and I'll leave you with that thank you

Channel: European Geosciences Union

Views: 6,400

Keywords: education, conference, outreach, science, Vienna, EGU, European Geosciences Union, Earth, Earth sciences, planetary sciences, space sciences, geosciences, history of the Earth, mass extinctions

Id: 0Py5HIFjdbg

Length: 35min 27sec (2127 seconds)

Published: Mon Aug 06 2018