 I'm really honored to be the non-mycologist in mycology symposium. I don't know most of the other speakers personally, but I certainly know their work and have used and benefited from it. And I really appreciate that. And I also particularly appreciate being here given that I took mycology from Dawn a long time ago. And I was trying to think what year that would be and I couldn't decide, but I realized for context I can specify that there was a question on the final exam based on the X files. So that should probably narrow it down a little bit about how long ago that was. So I'm gonna talk, as Dawn said, I'll be talking about fungi, but kind of on a larger scale and how fungi then interact with a broader world. I will talk about the fungal fossil record, what it's like and kind of how, what you guys have done have really changed what can be done with the fossil record. And yeah, I feel like I would best, I'd be disappointing somebody if I did not talk about a giant fungus. So I will include a little bit about that in there. But mostly as one, I did it while I was at Harvard. I at least started it while I was there as a postdoc. Even I didn't finish it until later. But also it's relevant to saying how the world's changed in the interim. But then I'm gonna then look beyond that and think about the carbon cycle and how fungi could interact with that over the long term. And then kind of delve into one particular way that that could be of importance. So to the extent that this is an introductory lecture, it's important to at least have some introduction. And I think the real important thing to say here is that fungi are really strange. The fungi are really weird in that we have three multi-cellular groups that dominate terrestrial life. And of those, we mostly just think about the plants and the animals in our daily experience and the plants, the producers and the fungi are the consumers. Great, along with the animals. And that's fine. They can be consumers too. But they're also like the plants that they have cell walls. So they can eat. They're eaters that cannot eat. And there's a word for that. It's osmotroph, great. But I feel like that kind of whitewash is just how odd that is to be a complex multi-cellular organism that has to eat and yet does not eat. And so everything has to be in solution. They become masters of modifying their environment whether that environment is the soil or that environment is another organism. They're masters at modifying it. And that really becomes why they've been entrained and suggest every large change over the last 500, 600 million years. At some point, someone has suggested that fungi have somehow been involved with that. Whether we're talking about changes in carbon, oh, you can't see my pointer yet here. Let's go laser pointer. Whether we're talking about changes in carbon dioxide through time and several large drops in carbon dioxide concentrations, big peaks in oxygen abundance at different points in Earth history, even changes in marine diversity of marine animal life. Fungi have kind of factored into those space as well. And that's really kind of gets into this larger issue of what's now called geobiology of how life and environments through time have interacted and shaped each other. So if fungi are this important, we got to look to their fossil record. And when we look to their fossil record, it kind of just looks like this. It's largely dominated by the plant fossil record. Anatomically preserved plants are a routine part of the record. What you're looking at here, these kind of darker bars, those are the tracheas of a fern. This is a petiole of a fern. It's 330 million years old. It's old. Here are some hyphae strung across, like a little festoon across there. That's what the fungal fossil record tends to be. It's hyphae. If you look inside plant fossils, there will probably be some fungi in there. But typically it's gonna be like this. And just like with deuteromycetes among living fungi, if you don't have the spores, if you don't have a fruiting body, if you don't have a sexual stage, what is it? And so there's lots of plant fossils with hyphae in them and there's just not necessarily much you can do with it. This turns out to be a very important fossil. You can see the clamp connections. This is the oldest Pacificomycete that we have in the record. So this is hugely important as a specimen, but you can imagine if this was 50 million years younger or 200 million years younger, it's just hyphae. We would have a million other examples of this and it would be of no significance at all in any kind of singular sense. So the record as it is studied tends to push the old things. Cause if you can find the first example of something, well then that means something. But after that first example of something, you're never gonna fill in the rest of the record because you can never see it in enough detail. So to continue a little bit with introduction, here are some fungi and this is remarkable how much this has changed since I took Don's class. When it was just Cetridium, my seed zygos on up and that was it. We know a lot more about the base of the tree and that's all just been worked out by some of my fellow speakers in recent years. But we can talk about how at the base of the tree, there are various things that are single cellular. They might have what are called rhizoids that do not have nuclei in them but they can kind of filamentously expand into their substrate that they're gonna be eating. They have zoospores which are flagellate. They don't have a wall, right? So this is like the one time they don't and then before they start eating, they add the wall. Again, fungi are weird. Why you would do that? I don't know. There are reasons of course, but so be it. Beyond that, we have the filamentous fungi. The basal branches don't have septa in their cell walls and then beyond that, we have the dicharion that do with the ascomyseeds and vasidiumyseeds. We have things like the mycorrhizal fungi that are busculars, mycorrhizae here, the glomerum microtina. Where those are located in the phylogeny has toggled back and forth a little bit in recent years between being with the mucoramicoda here versus being sister to dicharion. Maybe it's stable now. It seems to be getting more stable but that's kind of in here someplace. So that's what we have as far as phylogeny to think about. What does the fossil record look like of that? Well, again, since the fossil record of fungi comes from the plant fossil record, plants are the vessels for fungal fossils pretty much. We have to talk a little bit about that plant record. This is showing what this looks like through time, focusing on the early stages here. We have spores that indicate bryophyte grade lime plants going back to the Ordovician. So about 470 million years ago, 460 million years ago. The first macrofossils, and by macro, I mean about that big, are these things like coaxonia here in the slurian, so about 430 million years ago. As we cross in this Devonian here at about 415, 420 million years ago, we have larger plants that are clearly vascular plants. They get to be about that big. They're about a pencil and diameter, pencil within diameter. Very simple anatomy. They don't have leaves or roots or wood or anything like that. But by then the end of the Devonian, we have several groups of plants have large trees. You have seed plants and ferns and horsetail leaves, things and stuff like that. And then things kind of really take off from there. And the carboniferous will have likeopsid trees that we're gonna see a little bit more of that can be 40, 50 meters tall and so on. And then this will continue forward through the rest of Earth history from here. So after this carboniferous, which ends about 290 million years ago, we'll start to settle down more into a world that feels familiar to you, as far as conifers and ferns and cycads and stuff like that. And then of course, antysperms will come and ruin everything about 120 million years ago. And really kind of take off from there to the point that they now dominate most systems. So if we wanna talk about the earliest record of fungi, that's gonna come down to here and specifically a place called the Rainy Church, which is in Scotland. It's the oldest anatomically preserved biota that we have. This is a cross section of a plant and you can see all of the cellular detail. And if we look at the fungi included in these plants, it's kind of an interesting picture. This is the first chance that we have to really look at this and pretty much everything's there. We have chitrids and they're even doing chitrity things in the same way that you would bait chitrids with pine pollen or something in the modern world, there's some chitrids on a spore. We have various other things, blastoclads and doggonellies and we have the actual mycorrhizae, the glomerum, mycotina and stuff like that. They're present. And there's even an ascomycete. And if you have an ascomycete, even though we don't have obesityomycete, they're the dicaria, they're sibling lineages. If you have one, the other one, at least as a lineage exists. So when I first kind of became aware of this record, and I was interested in what funds I were doing through time and all these things, it felt like, well, here's our first chance to look and we're already done. We got everybody. What can we do with this? We're never gonna fill in the later record and it feels like everything's here. Now, I was kind of a callow youth to feel that way. There's plenty of things I could have noticed. For example, in the modern world, the dicaria are 98% of everything. And back here, there's exactly one ascomycete and obesityomycete, right? So some things have changed. I didn't notice that. And certainly, I also did not notice that we had some things, but there are plenty of things we didn't have. And a lot of people have put a lot of work into filling this in. People like Christine Struleau there again have described another number of lineages that we just did not have. But from my perspective, I felt like, well, everything that we could expect to see, we see it. And that since we're done, so if we can't focus on what you might expect to see, what we should instead have to focus on are the things that you wouldn't expect to see. And that gets into this thing. Yeah, it's really big. It's eight meters tall as far as the largest specimen. This is proto-taxides. It's known throughout the Devonian cosmopolitan. It was originally described as a conifer, proto-taxides, right? This is the Dawn U Tree or whatever. It's made up of little filaments. It was first described about 150 years ago by Dawson, one of the great early paleontologists of the North America. And then since then, it's been controversial ever since, where in paleobotany, a controversy means a paper every 15 or 20 years, but none of those papers have agreed with each other for a very long time. So it's been called a conifer. It's been called a sea plant. It's been called a lichen. It's red, green, brown, algae. It's been called a fungus. But what do you do with this, right? The most recent thing at the time that I started working on this was a guy named Fran Huber in 2001, he was at the Smithsonian. And he described it as a fungus, particularly at the city of Mycete, like a bracket fungus. When I looked at this, I felt like, well, there's no way. If people have been arguing about this for 150 years, there's nothing for me to add as far as the sources of evidence they had been using, but maybe we can look at alternative sources of evidence like the geochemistry of these fossils. So we looked at kind of a broadband of just geochemical things that could be helpful in various ways, not knowing what would work. And what turned out to be very useful were carbon isotopes. So these are stable isotopes. There's no radioactivity involved or anything. This is carbon 12 versus carbon 13. And different metabolisms will fractionate the carbon 12 versus carbon 13, they'll favor the lighter carbon 12 versus 13 to various degrees and so on. And so the way this is done, when you're working with fossils, you always have to worry about the fact that this thing is 300, 400 million years old, it's been cooked. When you look at the chemistry, are you looking at remnants of the original organism or are you looking at the history of how it's been cooked for 300 million years? And to get around that, what we did is we only made comparisons within locality. So at least know that they share the same history. And if they've been cooked in a particular way, they would have been cooked together at least. And what we can see is that, the plants are consistent and so on, but the proto-taxides can be enormously variable in this carbon isotopes compared to anything else. So again, you have to first worry, is this real? Or is this some kind of signal of how the thing's been altered over time? Looking at the organic chemistry, all the proto-taxides is very similar to each other. It's different from vascular plant fossils. It's different from the coal. If we look at elemental abundance, this is look at carbon and you can see the little tubes and stuff like that. There's not, there's carbonate or anything else that would obviously screw up the carbon isotopes. And they're all well preserved. Across this whole isotopic range, they're well preserved fossils. So the signal appears to be real. And if that's a real signal and you have a signal and a grains that broad, what that basically requires is a heterotroph, something that's eating rather than being a primary producer. If you're a primary producer, you'll have some range but it'll be relatively narrow because you're getting carbon dioxide from the sky in one way or another. And that metabolism is gonna constrain how variable you are. A heterotroph, though, will look like whatever eats. If you look at a human being from Europe versus a human being from America, they will look quite distinct based upon their diets. Here, we're mostly corn syrup and stuff like that. That's the American way. That's the C4 plant. So Americans tend to look like C4 plants. You go to Europe, they look like C3 plants, like wheat and sugar beet instead of sugar cane, that kind of thing. So when you see a range this large, that's an eater. So if this is a terrestrial filamentist heterotroph, that sure implies that this is a fungus. There's not a lot of other options. It could be something entirely extinct and there's no way to rule that out. It's not an Umei seed. That's the other filamentous saprophytic thing that you can imagine that would be an eater. That thing would look more like plants because it has cellulose cell walls and this doesn't look like the plants. So the best option here is a fungus. And that kind of gets to where I wanted to go with this particular fossil in this context of just how much things have changed in the last 15 years. So it's a fungus. Now what? Fran, Huber in 2001, he described it as a Bacidium Icy. His evidence was pretty non, it was a fossil that he'd been interested in for decades and he had dealt for decades with people going, no, no, no, no, that's too big, that can't be that. And so he really emphasized things like Bracket Fungi that could be a robust thing that last years and slowly grows and stuff like that. And he described it as a Bacidium Icy and he made specific comparisons to various Bracket Fungi and stuff like that. He was doing this in the late 1990s, published in 2001. So when I did this study in 2007, that was in the middle of the heyday of how much the fungal phylogeny has changed. And I wanted nothing to do with trying to say what this thing was phylogenetically. The geochemistry doesn't constrain it anyway. So there was nothing to say there until that phylogeny settled down in any case. So we just kind of went with what had been said, but now that the phylogeny has settled down, it's clear that the points of comparison that were being made are totally off base. He was looking at polypores and the Garakales that aren't gonna show up for 200 million years later. So there's no point of comparison there that actually made sense. It was the best he could do as a shot in the dark without that phylogeny and without any time calibration of the phylogeny certainly. And he did what he could with what was available. But now we know that those points of comparison couldn't possibly work. And actually, most recently, it's been compared to Ascomi seeds. There's another fossil that's been described. It's not, this isn't airtight, but it's an Ascomi seed. These are in association. They're not attached, which is a common problem in the fossil record. So they might be the same thing. They might not be the same thing, but they're specifically comparing it to Neolectes in the, to find in Micotina. I never have to say these words out loud. I'm just reading. And on some level, just aesthetically, I kind of like this because in this lineage, it's mostly yeast or kind of scantly hyphal things. And then there's one genus that gets put all the way up in its own class that makes these macroscopic structures, right? So why not, right? What is, as a comparison proto-taxides, whatever it is, is an anomaly. It's not going to fit with the city as easily even if it is there. And it's not going to fit with the Ascos as easily even if it is there. And it doesn't have to be in dicary at all. It's not like it's set date or anything like that in those filaments. So wherever it goes, it's going to be an anomaly. What I find particularly interesting is that when this was suggested, just like a couple of years ago at this point, they were clearly very aware of phylogens like this. And they knew what they had to work with and what they didn't in the way that Fran didn't 10 years before that. So it makes an enormous difference, the context that's now available to us as far as the phylogenetics. And there's so many questions I can now ask about the soil biota 400 million years ago because of this context that's now available. And so where I want to go from here is just kind of delving into the fact that this is a wonderful new source of information, but we still then have to treat it as another line of evidence that is useful in the earth sciences. So this kind of the same work as far as time calibrated phylogenies, the Bacidium icetes. When this came out, it provided kind of a new life for some old ideas. This paper is from the early 90s. There were papers saying this kind of stuff back in the 1950s actually. And what's being suggested here is that what this is shown in the black line is this is coal abundance through time. And so this is the carboniferous here. And there's a reason why the carboniferous is called the carboniferous. That's where the industrial revolution comes from. This is all the dirty faces and every dick in the novel you ever read. This is where this all comes from is from the carboniferous period. And notably the Cidium icetes which are the primary wood rotters starts showing up both in the record and now from molecular phylogenies kind of thereafter. So the idea was floated and has been floated repeatedly over the decades. Then maybe what's going on here is that the things that digest lignin that the robust recalcitrant molecule that's found in wood wasn't there. And so we were accumulating coal because there's nothing to digest all that plant matter. So if we look at this, every cell wall and every plant has polysaccharides in it like cellulose here, which is just sugar is strung together. Lignin is a polyaromatic gemesh that's joined together every which way and so on. And it's added to those polysaccharide cell walls but this is much harder to attack entomatically. And this is beautiful, beautiful work that's continued since this point as far as actually looking at all the enzymes involved in that and where they are and the phylogene stuff like that. So it's hard to do and sometimes I figured out how to do it. But then so what do we do with this going forward from here? So yes, Lignin has been recognized as being a very abundant contributor to coal but the way you study that the way organic geochemists have studied that is with relatively young coal. If this is looking again at the plant fossil record through time and to study how that coal was formed they want immature coal and then more mature coal. And so they want to look at the ontogeny of the coal and how the chemistry changes. You can only do that in young coal. So you look at those studies and you're looking at chunks of wood in the coal and then seeing how the chemistry changes. So that doesn't mean that Lignin is everything. It means that Lignin is everything in the coals that they're looking at. But what we care about is back here. 200 million years earlier, the carboniferous. So these are totally different floras. They're totally different plants involved. So what do these plants look like? These are all seed plant dominated. We know that they're woody and so on. What's going on back here? Well, this is the time of the crazy Dr. Seuss trees. They're giant Lycopsoids. Lycopsoids of course are still with us but they're the herbaceous things. These could be enormous trees, 40 meters tall, two meters wide. You look at the anatomy of these things. This pie piece is kind of showing that. This is the wood, this little bit in the middle here. All the rest of this is primary tissues and some bark. This is showing us an actual fossil. Here's the wood, the overall plant that would be kind of squashed all the way off the sides of the screen there. This is all other stuff. It's bark and stuff like that. It's completely different from something like a seed plant that really is abundantly wood. What's the chemistry of this stuff? Looking at the chemistry of a fossil like this with organic chemistry here and what this is doing is it's using the fact that X-ray frequency of when you bombard a specimen at different X-ray frequencies, you'll ionize it depending upon the organic chemistry that's present. So the spectra what it's showing is the relative abundance of different types of bonds. And because you can actually do this with imaging, these are individual cells in that fossil there. We can compare different tissues. And again, these are tissue comparisons within this fossil. We know it's helped the same history and so on. And what we can see is that all this bark stuff is very different chemistry from the wood. We know this is lignified. We don't know what this is. These look nothing alike. This is not lignified. This plant is the dominant contributor to most cold carboniferous. And it doesn't appear to be lignified. It'll have a little lignin in this wood, but that's it. Okay. So lignin is not gonna be a big contributor to those carboniferous coals in the first place, right? Those plants, those arboricinlicopsis, they can be 70% of the biomass. That bark alone can be 50% of the biomass. It gets heavily kind of concentrated in these lenses of stuff. So when we look at kind of coal distributed through time, this is coming right in the middle of all this. It's not dominated by lignin. If we look across individual coal horizons across the carboniferous here, there's actually a big turnover from the light gray here are these arboricinlicopsid trees that would not have been lignified heavily. There's a turnover. These kind of go extinct, at least in Europe and North America. And they're replaced by tree ferns. And the tree ferns would have been lignified, right? So there's a big turnover in the biochemistry inputs. And apparently the biochemical inputs don't really matter. There's coal because there's coal. It doesn't necessarily matter what's going into the coal the way you might expect. So it's not about the lignin. We can take that further and say that we definitely had coal rot, wood rot before the carboniferous. This is some of the first wood. This is colycelon. It is the first abundantly woody plant. This is the Devonian age now. So it's right before the carboniferous. This thing is chewed up. It's rotted. If you look at this microscopically, this is the same specimen. There are the hyphae in there. Now you could argue that it was rotted by bacteria or something, because bacteria can do it and that the fungi are somehow benefiting from it. This is not... There's no clamp connections here. We can't identify this as a basidium icid. So it's not necessarily related to modern wood rots, but it's a fungus and it's in wood that's rotted. It feels kind of like a wood rot to me. And this can be quite comparable to some modern rots as well. So it's absolutely appropriate to ignore this fossil if you're trying to use fossil calibrations of a phylogeny or something like that because we don't know what this is, right? But if you're not interested in this as a fossil tie point, if you're interested in it as part of the earth system, there's undoubtedly rotting wood before the carboniferous. We can also see this in the carboniferous because if you look at these coal fossils, they're overwhelmingly dominated by roots and not shoots. Now why would that be? Because the way this organic matter is getting preserved is if you are buried in anoxic muck that retards decay. And the roots are burying themselves in the peat versus the shoots which are falling on top of the peat and then have a chance to decay before they end up getting submerged to the point that they're gonna be preserved. So this all is pointing to, it's not about the plants and what's the input you need the plants, they are the coal, but it's really coming down to an environment. And we can see this in one more way. This is a different graph from the one we looked at as far as coal through time. The first time I saw this graph, it really surprised me. A colleague of mine, Shannon Peters made this and I asked him, can you just print out coal through time? This is what it looks like. Did all those spikes, I was not expecting to see it all but then you wait 30 seconds to go, yeah, actually that does make sense because what we're looking at here is individual basins where you could preserve coal coming in, filling up and then going away and then you have to wait for the next basin. So that's one thing to notice. Another thing is that in recent times the last 50 million years, 100 million years it's kind of co-equal with how much coal is being produced back in the Carboniferous. We're still making coal, we can still make as much coal. So it's not about the inputs, it's not about who's degrading it, it's about having an environment where you can store the stuff. You both need a wet environment so that it won't decay and you need a hole that you can fill with the coal, otherwise it's gonna erode away and just won't be part of the record. So what is going on here? What is going on here? We won't get past anymore, there we go. This is unique in Earth history. The reason we have so much coal from this time is it is the one time since we've invented plants when we both had a wet tropics because we do not always have to have a wet tropics. If you go back to dinosaur times, Jurassic times there are no rainforests across the tropics. It's more like savannas all the way across, it's summer wet all the way across. But we had a wet tropics back in the Paleozoic related to the fact that we were also in the Niceties then as we are now. But we were also actively forming Pangaea which means there were lots of tectonic basins that could be filled in these ever wet places where you can store the coal. Now we have a wet tropics but the tropics, all those continents tend to be surrounded by passive margins so they don't have the tectonic basins that could be filled with coal. So this is really a unique time. You go globally, this will all get smoothed out but you have the most coal in the carboniferous and the Permian and it's declines since there but it's strictly based upon environmental signals. Okay, one last thing to think about here and this is kind of then lead into a larger topic of the how do we think about these things and what should we be thinking about the fungi and how they could or could not have changed the world is that lignin is a big fraction of a vascular plant on average is about 20%. Productivity was probably lower in the Paleozoic. I think it was quite a bit lower in Paleozoic but even then we're probably still talking like three gigatons of lignin made per year. The end of the carboniferous is 100 million years after the first things that had vascular cells that would have been lignified. You can't just do 100 million years of a couple gigatons a year and not have that balance out, right? In the entire geologic record, there's about a thousand gigatons of coal. So you can do the math, right? 100 million versus a thousand is not gonna work but more importantly, that would just be a big weird imbalance in the carbon cycle. Here's the carbon cycle that you guys, everybody's seen at some point and a very important part of this is that everything balances out. Respirations is 35, assimilation is 35 and so on. There's no big numbers here that are not balanced out by an equally big negative number. So this would be a huge imbalance in the carbon cycle to do that and you can't just do that. So this is looking at an imbalance in the carbon cycle at modern pre-industrial CO2 versus 10 times modern CO2. And if you just impose a 25% imbalance, what would happen? And what would happen is in the less than a million years, maybe a million years, you totally would crash the planet. And the reason for that is that CO2 matters in more ways than one. It's also a greenhouse gas. If you had 25% too much weathering, which is a drawdown of CO2, you end up a snowball earth, you'd end up Mars or something very, very quickly. If you had too much volcanic outgassing of CO2, we'd end up Venus, we'd end up boiling off the oceans. Either way, you're gonna kill the planet, right? And so it's not just that this would be bad. It's that we can know this didn't happen because we're still here to wonder about it. There cannot have ever been imbalances like this. The one time is snowball earth and then the earth came out of it thereafter. But certainly in the history of complex animal life over the last 500 million years, that's never happened. So we know that there couldn't have been any imbalances like that. So this is 25%. What happens if we look at a little bit smaller? So we kind of took their exact same thing and we just made it a 5% and a 1% imbalance. And yeah, if you get down to a 1% imbalance, you can kind of kick that around in the system for tens of millions of years until some other imbalance takes over and stuff like that. So you can kind of drift on the currents a little bit if it's small enough. But the key thing to keep in mind here is that no one sells their science paper on we got a 1% imbalance in deep earth history. It's always some big crashing destroy the world kind of situation. Certainly like if you look at the popular media presentation of things that have happened in earth history, they're always making big deals out of things. And you can almost by default when someone suggests a very large change to the system that it didn't happen. Because if it did happen, it would have killed the planet. Changes can happen, they're gonna be small changes and they're things that have to happen in equilibrium. Or you can have a big change as a perturbation, that's fine. A big meteorite impact, that's a perturbation. The existence of humans, that's a perturbation. But perturbations are transient, they will go away. They have to stop and they stop quickly. So this is a modeling of that where they just dumped 50% extra carbon into the system and things went crazy. And then they settled down in less than a million years. We have real life examples of this. This is the paleosine thermal maximum. It gets a lot of press for being the most recent in time equivalent to what we're doing to the atmosphere now. And what did it look like in practice? Yeah, it's like 100,000 years. We dumped, something dumps. We don't even quite know those mechanisms yet. But something dumped, a lot of greenhouse gases into the atmosphere. And yeah, 100,000 years, it was done. Taken up in whatever kind of mechanisms there were as far as deposition in the oceans as carbonates and someone like that, but it's quick. And it's ultimately tied to the fact that the residence time of carbon in the system is about 150,000 years. Anything's gonna be resolved in a couple of terms of that crank. So this is important to think about because when people are making these models, you always have to remember why they're doing it. I'm a consumer of these models. I don't make these models. But what I'm interested in is not the same thing that these guys are interested in. Their bread and butter usually tends to be actual atmospheric composition. They wanna talk about giant dragonflies with oxygen and they want CO2 as a big deal. So they're modeling that. But the things that actually interest me as far as how the ecosystem would have worked, it's not this, it's the fluxes through the system. It's how much weathering there is, nutrients and stuff like that. And that's included in all these models, but it's not the point. So they'll talk about drawing down CO2 and so on. But they're talking about these graphs. They're not talking about what would actually happen in practice. So if we look at what that would look like. So here's the carbon cycle I showed you. This is the short-term carbon cycle. This is the ecological carbon cycle. This is the long-term carbon cycle. If you squint, there's almost no overlap between what is listed in one of these graphs and the other. They're both the carbon cycle. Volcanoes are in both. Great. And the reason for this is that there's all these big fluxes in the short-term carbon cycle, but they're not necessarily big amounts. And they keep going, right? The biomass, the forests, you burn down the forest, it's going to grow back. It's kind of a hamster wheel. How much biomass there is isn't going to change all that much through time. But you look at some of these other numbers, the huge numbers, those are the rocks. There's very small fluxes in and out of those, but over geologic time, those are the things that end up mattering. And then all the actual life stuff are just kind of cycling through. And so the big players here are the weathering of silicate rocks, which is a big drawdown of CO2. You take granite and stuff like that, delts bars, mineral grains in that granite can be weathered with CO2 in solution. It'll form clays, that's where clay comes from, and quartz and stuff like that. And so you end up, you take a granite and you're knocking it down to sand, quartz sand, plus clay minerals, and that's the consumption of CO2. There's also a lot of ions released, they wash off to the ocean, eventually become carbonate and rolls up limestone. And so we can look at a system like this and like in this model of CO2, which has some backing from proxy data, this big drop off here is thought to have been caused by the evolution of trees and their fungal symbionts and how together they all are pumping organic matter down in there, both as organic acids and chelators, but also just as biomass that perspires and then decays and so on. And adding all that CO2 at depth results in this big drawdown of CO2. That's been suggested at other points in this curve as well. So there's one early on with the first land plants, about 5, 4, 180 million years ago, those bryophyte spores, those might have been the first one to have our bushy or mycorrhizae, that's the thought, even though we don't have any record beyond those land plant spores. That's thought to potentially been an important drop. And then here we have the evolution of angiosperms and nectomycorrhizae over the last 150 million years or so. But so what would that mean in practice? What would it actually look like? I just said that these numbers can't change, that you can't have huge imbalances. Well, this feels like this should be an imbalance. Well, what would actually happen if you add these roots to the system is you have to kind of put it in a modeling perspective. And again, there's nothing profound in what I'm saying. Any model of the earth system, the first equation is gonna be inputs minus outputs equals zero. That's gonna be the first thing. It's just a basic of the way these models are constructed. But so the outputs, well, I guess the inputs to the external system are things like volcanoes. Whatever comes out of the volcanoes has to come back down. That's all that means. The mass balance is based upon that. There's some other things, but the big input is the volcanics and one of the big outputs is the silicate weathering. So this leads to a system like this. However much is coming out of the volcanoes has to come back down and we're only considering silicate weathering right now, the weathering of the rocks. And you have some feedback between how much CO2 is in the atmosphere and how much weathering will get done. So that's kind of reflect this slope here. And the equilibrium is gonna be wherever those two balance each other. And if you have some disturbance of that system, you add in the plants. Yeah, that genuinely is gonna start sucking more CO2 out of the sky if you add in those deep rooting plants. But what does that actually mean in practice is that they're now drawing too much CO2 from the sky relative to what's being put in. That's gonna draw down atmospheric CO2 until you reach a new equilibrium. And then what's changed is the CO2 concentrations. That's what the modelers are worried about here. What has not changed is the actual weathering fluxes and nutrients through the system and that kind of thing. That doesn't change except as a transient perturbation. Now you could change those nutrient fluxes if you change the inputs. If there's more volcanism, then more CO2 has to come back out and there will be more weathering. But this is something that fluctuates through time. There's no directional change to be expected there. You could also have other changes by adding things in like coal deposition, but that'll be in the opposite direction. That's actually gonna have to detract from the weathering. So when people talk about plants coming into the system and weathering rocks and making more soil and drawing down CO2, in actuality, they can't do that. They can only change the equilibrium of CO2 concentrations. And if anything, they would have lowered the weathering fluxes because some of the CO2 is being shunted to making coal instead of the silicate weathering, the weathering of the rocks. So this is not just kind of semantics. This has real world applications, at least real world as far as the balsa record applications. I'll give you two examples quickly that have nothing to do with fungi just to show that this is not just about, this really is how the system, this is important for the whole system. This is marine diversity through time, Shelly marine invertebrates. You can see these two big jumps here. Both of those have been suggested at various times be related to the evolution of the land biota, either the first land plants and their mycorrhizal fungi or the evolution of antiosperms and different mycorrhizal fungi. And with the idea being of once you do that, there's more weathering and more flux of nutrients to the oceans and then that can foment diversification in the marine realm. I've said this myself, right? I'm as guilty as anybody of having said that. But once I think about it more like, no, actually that can't possibly happen because that would mean permanent huge changes in the weathering fluxes and there's no basis for saying that. That would be a system out of balance. Similarly, and these are papers that are just published in the last years or so looking at sedimentology and the buildup of sedimentary rocks, it's been recognized that there's a lot of mud, a lot of mud specifically in the last 450 million years or so. Mud involves those clay weathering products. So this is based upon the weathering of these rocks. This is a drawdown of CO2. They see this huge increase in mud and two things are suggested. One is that some way there's mud retention on land. So we're seeing more mud even though not more mud is being produced or there's more mud production. They can, you know and they entertain both without rejecting either. But no, this 25 increase in mud production that's saying something about an enormous increase in chemical weathering that can't happen. And interestingly, these same authors already have completely worked out beautiful systems as far as how mud retention would have changed. They'd already done it before this paper about how with plants you get flood plains where you have this flux of sediment rather than just being shunted off to the oceans it's spreading out during flooding events across these flood plains and being retained on land. So they have a beautiful physical mechanisms for this mud retention. They don't have to worry about this, right? And then that will also start to matter then when we think back to the biota of we have this system here and we do have the addition of coal through time. So if anything, we have to worry about plants lowering the availability of nutrients. Okay, so the evolution of the plants and the fungi and the biota as whole it should have a big impact upon what's going on on land as far as the weathering and CO2 concentrations but those are equilibrium CO2 concentrations. It's not going to change the actual weathering fluxes because it can't in the permanent way unless you do something like change volcanism or so on. And this has real implications for thinking about how different parts of the system work the falser record, sedimentary geology and what a fungus could do or not do. And yet, and this is the kind of the last thing I want to really kind of home in on here is and yet there are times when it sure does feel like there's a change in the nutrient fluxes. People talk about this a lot of since the Med Mesozoic so like the last 150 million years or so coming through to the present it just feels like there's more stuff there's more higher productivity all these things are going on. There's a much higher diversity and that spans plants, animals and fungi. It feels like there's a lot more just biomass out there and so on versus earlier in time. What's going on here? Now, this is often attributed to the evolution of flowering plants and I could totally just support that, right? That would be very unbranded for me. I've worried about the evolution of flowering plants quite a bit over the years and some of the anatomical characteristics that might go with higher productivity within the flowering plants. And yeah, that's sure. Why not? In the same way that flower biology could be involved quite a bit in the species diversity. So between the floral biology of flowering plants and the vegetative biology of flowering plants this leaf here in the background is a flowering plant versus a fern in the front. That might kind of account for all this and yet you can't just have more productivity from the flowering plants. That sounds nice but in practice all photosynthesis gives you a sugar and you can't make an organism out of sugar. You need the other nutrients. You need nitrogen, you need phosphorus. So if productivity is going up I wouldn't see the angiosperms necessarily as the cause. I would see them as another effect. They might be the best ones to respond to a changing world but I don't think necessarily they can do the changing. The world has to change and then they're the ones taking advantage of it because they completely taken over the world in the last 100 million years. They went from nothing to being 90% of everything everywhere you go. So there are other ways we can get at this as far as thinking about how has productivity actually changed or not and that gets back to thinking about the fungi. This is looking at nitrogen fixation among lichens in the leucanaromyocetes and then ectomycorrhizae in the gericoma catina and all of these evolutions of this of metabolisms symbiosis that involve either nitrogen fixation or nitrogen scavenging from the soil and so on. They're really diversifying over this same time period. This is showing the number of gains in ectomycorrhizae specifically the ones in the gericoma catina and it's all kind of concentrated whether there's a lot of branches there and this is whether it's kind of branches per time or appearances per total branch length available per interval, it's drastic and later. We've seen that in other recent papers shoot that Vargas paper that I'm gonna put up. They show that similar diversification starting in the Jurassic and moving forward from there. If we, this is just the two lineages the basidios that have the most ectos and the ascoes with the most lichens. If we look more broadly and we also look at the partners in these associations there's a whole bunch more that we can add to this. Again, these are all coming from other people. In this case, there are other people's time calibrated phylogies but all of this everything on this graph is coming from time calibrated phylogies. There's no way I could touch any of this if I was just using the false record. And again, it's really taking off over the last 150 million years and there's maybe a couple of stragglers in the earlier record but that's it. And when you compare that to how early plants are on land it's really kind of striking how this is all suddenly being added towards the end. This wasn't all back there in the Paleozoic. So yeah, that kind of feels like there's more going on. Now this is focusing on nitrogen. Nitrogen comes from the sky. You can always fix more nitrogen as long as you have enough photosynthesis or whatever sugars to support the nitrogen fixation you can do it. Phosphorus comes from rocks. The only way to get more phosphorus is from chemical weathering of rocks and that's the thing that I said was a problem as far as you can't have unbalanced changes to those fluxes. And here we have a situation where we have all this extra nitrogen in the system that sure would imply extra phosphorus. Is there a way to go about increasing chemical weathering? Even though I said that you can't do that. You can do it as a fluctuation as a transient perturbation. You can't have a permanent 150 million year change like that and yet I kind of need one at the moment. So is there a way to go about getting that? Well, as we said before, you can add more volcanism. And sure enough, there is more volcanism in the Cretaceous but again, it's transient. We don't have more volcanism now and yet these processes are still going on. And that gets us to the alternative which also kind of reared its head earlier which is another thing we added to the system in the Paleozoic was the coal. Coal has to suppress the silicate weathering. It has to bring this down. And so as we all add this to the system what's gonna happen, right? So if we imagine the continents, the continents have been around going back more than three billion years in various configurations. What we probably buy about three billion years ago, three billion years ago, had about roughly what the continental mass that we have now. It's been sitting there the whole time. What we did not have was a big, complex productive land biota. We had productivity in the oceans and you can bury organic matter in the oceans and you have continental shelves where you can save some of it but anything buried on the sea floor is gonna get recycled quickly because that sea floor subducts and it ends up coming back out of volcanoes someplace else. Continents don't go down volcanoes. So for the first time, we have a huge bucket which are all the continents that we can worry about filling with organic matter. And so that's gonna last for a while. The accumulation of coal once coal is initiated but there's a limit to that bucket size. There is a rock cycle and rocks tend to get eroded. You can't make newer rocks without eroding old rocks. In general, rocks tend to live, continental rocks, about 100 million, 150 million years on average before they're eroded. So what we're gonna end up with is a system here where at first, once you turn on the deposition of coal, you can keep on doing it for a while in an unbalanced fashion and it's only gonna end up subtracting from silicate weathering. Over time, you're gonna start eroding the coal that you've already deposited. And at some point, you're gonna reach a steady state where as much as you're depositing, you're eroding someplace else. And then that kind of goes away as a useful sink in the system. So maybe it's not a question of amping up all that nutrient fluxes over the last 150 million years. Maybe it was suppressed earlier and we're removing that suppression over time. So what would that look like? So this is a very simple model to look at. This is just a step function of adding coal to the system and then continuing forward for 600 million years from that time zero there. This is how it would accumulate at first, very rapidly. But then over time, you're gonna start eroding the coal you've already deposited and you'll reach some steady state. It'll take a long time, but you'll get there eventually. So what will that do to the weathering of rocks, which is the source of nutrient flux like phosphorus is gonna drop very suddenly and then it's slowly gonna recover and all these different dotted lines here, those are just kind of sensitivity analyses for how long we're saying the rock cycle is from 50 to a 250 million years for the average half-life lifespan of a continental rock. So this is a very simple model and this would suggest that yeah, if we initiated coal about 320 million years, 350 million years ago, we should start to get it to a situation where we've lifted that suppression around 200 million years, 150 million years ago. So this really could be a change in the world without putting us out of equilibrium and giving us some chance to have a more kind of longer term effect. Okay, so this is a more complicated version of this, but it's still very simplified versus the big complicated models that people do for the deep time earth system. This is more like what coal deposition through time really looks like. This is what the accumulation would look like. And then this shows what those nutrient fluxes would look like. If we first focus on the black line, you can see it kind of come up and come down and stuff like that, but you can still see the suppression through the later part of the paleozoic, the carboniferous and the time period thereafter, and then it's only recovering later on. This big divot here reflects a period after the permotrastic extinction, which was the big deal, biggest mass extinction, much bigger than the one that took out the dinosaurs. And there's no coal thereafter. And that's often treated as a symptom of the extinction, but it's important to also recognize that that's in itself is a big kind of deviation of the carbon cycle that matters in its own right. It's not just a symptom. It can affect a lot of other things. And that's why there's this big pump up here because suddenly you have a lot of coal that exists, but you're not adding new coal to the system. So you get this pump up here and then it kind of comes back down from there. We can take this one step forward and make it a little bit more complicated where we have variable outgassing. This is variable volcanism through time. And so that kind of, again, you can still see the pattern, although there's that peeking in the cretaceous there that around a hundred million years ago. If we add in variable volcanism, we should also recognize that a lot of that is going on in the oceans and we're making new seafloor. And new seafloor will weather regardless of what's going on in the atmosphere based on just the hydrologic cycle working through that crust. And so what ends up happening is you get the gray lines instead. And it's all this roughly the same curves, but you can really see the suppression standing out in the late paleozoic and the carboniferous in the Permian. And then it's only thereafter that things recover. So all of those evolutions of nitrogen fixation, nitrogen fixation goes back, the cyanobacteria goes back two billion years, but all these symbioses, they're all accumulating fairly recently. And this might be a potential explanation for that. Now that's a really odd way, I'm sure, to think about the carbon cycle for anyone worrying about modern soils and modern fungi and stuff like that. And it's important to recognize that the world really is complicated. And I'm not trying to gloss over that. It's granular, it's all these different environments, lots of different things happen. This is a recent paper showing the distribution of ectoes versus arbustulars versus nitrogen fixing trees with nodules. There's a lot of complexity there. Pioneer plants in new soils are different from the things that will then later be established on those soils and so on. But this is a general way that kind of will lift all boats and push everything on average in equilibrium towards nitrogen being more limited and it could help explain why there's so many parallel evolutions of these metabolisms based on nitrogen only over recent history, where recent is expressed as a paleontologist over the last 200 million years. Okay, so overall, yeah, there are likely to have been some semi-permanent increases in weathering fluxes over the last 200 million years, but it's not from volcanism, which is gonna fluctuate. It's a consequence of what already happened when we first established those systems. So we make complex, stressful ecosystems, their first chance to flourish, as they're being created, they're actually suppressing themselves, right? It's the same plants that are kind of creating the coal and so on. And then it's only as we come out of that that we see all this diversification among the fungi, among the plants and among the animals that reflects these long-term changes in the cycle. Okay, I will stop there. I do wanna thank everybody I've worked with. This work I discussed spans like 15 years. So I would like to call it Matt Nelson, who is the actual mycologist among all of this. He was a former postdoc. He's now at the Field Museum and then various other people. Dan Ibarra is a geochemist. Mike Antonio is a student of mine and then we get into the people where I was the student who have all been very helpful through all of this. Okay, I will stop there and I am very happy to entertain any questions.