Wisconsin Public Television University Place Wednesday Nite at the Lab  Patrick McLaughlin Catastrophic Geological Events In Wisconsin  November 2, 2011 UP653     cc >> Tom Zinnen: Welcome, everyone, to Wednesday Nite at the Lab. I'm Tom Zinnen. I work at the University of Wisconsin-Madison Biotechnology Center. I also work for UW Extension Cooperative Extension. On behalf of those organizations and our other sponsors, Wisconsin Public Television, Wisconsin Alumni Association, the Science Alliance here at UW-Madison and PLATO, welcome to Wednesday Nite at the Lab. We do this every Wednesday night, 50 times a year. Tonight I'm delighted to be able to introduce to you Patrick McLaughlin with the Wisconsin Geological and Natural History Survey. Patrick received his master's and his PhD from the University of Cincinnati, finishing up in the spring of 2006. His focus is on the architecture of marine rocks in eastern North America. His research currently focuses on the record of hydrosphere, biosphere, lithosphere interactions; in other words, water, living stuff and rocks. 

[laughter] Especially the Paleozoic rocks, which I interpret to mean really, really old in the metric fashion, here in Wisconsin and in the surrounding region, and also sedimentary ore deposits, and groundwater transport and contamination. I'm not sure, but when I go to the boundary waters and I get to camp on those wonderful, huge old rocks that are out in the Canadian Shield, are those the kinds of things you might be talking about tonight? >> Those are really old! >> Those are really old. [laughter] Please enjoy me in welcoming Patrick to Wednesday Nite at the Lab. [applause] >> Patrick McLaughlin: Thank you. It's nice to be here and again thanks for coming out in this fall weather. As Tom said, I work for the Wisconsin Geological and Natural History Survey. It sounds like you'll be hearing from more of us soon. We study the rocks, soil, waters of Wisconsin, and we do that for many reasons, but in part to help inform policymakers about environmental issues and hopefully provide them with a bit of context from natural history. And so tonight I'm going to talk a little bit about providing some context.  We want to go back one. 

There we go. About environmental changes that are happening today and that are happening fairly rapidly. Today, we are in a state of global climate change. We are in a state of global warming. And that is shown here in a graph some of you may have seen before. This is a published plot of temperature, average temperature for the northern hemisphere, over the last 1,000 years, and you can see there's a marked increase, about 150 years ago, starting with the industrial revolution, towards much warmer temperatures. Why is that? Well, there's pretty good consensus in the scientific community now that greenhouse gases are the primary culprits that are leading toward this warming. We have CO2 and methane as two of the major contributors. Notice the C in both of these, CO2, and CH4 is methane. Those are both carbon molecules and the carbon is coming mostly from the burning of organic matter or the transition of organic matter into a gaseous phase. 

It comes from lots of different sources, mostly associated with human activities. On the lower here, I just added a little bit of an artistic rendition of Chicago in the summertime, now, from a Chicago resident. Smog and gas, industrial activities, just driving cars are contributing to this build-up of greenhouse gases. >> Can you account for the drop? There was a drop in the middle of the 20th century. It's fairly significant. >> Yeah, I don't know. On this graph, you know, I really couldn't tell you what is significant and what's not, actually. But that's a part of the talk, is kind of assessing, again, gaining some context. What is significant, what's not. So going forward, you know, what's going to happen is on a lot of people's minds with global warming. 

What does this mean for changes in environment and things like that? We've got the Intergovernmental Panel on Climate Change, IPCC, doing lots of modeling to try and assess, firstly, what the warming is going to look like, and there's various scenarios here that are shown in these different colors. These are different trends. They're based on the amount of industrial growth. How much more greenhouse gas is going to be pumped into the atmosphere is largely going to depend on where these trajectories go, but you're looking somewhere between just a little warming in terms of degrees Celsius to three and more degrees Celsius. Now, this model is just based on anthropogenic delivery of greenhouse gases, industrial activities, and driving cars, and things like that. This isn't taking into account other possible natural feedbacks in the system. So you need to keep that in mind. So that's kind of where the uncertainty comes in here. How is this going to go? There's other folks who are saying right now there's a lot of hype about perma frost, melting of perma frost, that below the arctic ice in the northern regions there's a lot of methane trapped in perma frost and as the ice melts it's going to release a lot of methane. That's not included in this chart. 

So there's a lot of side effects that are potentially involved in this process. And so if we go back and look at geologic history, we can look at essentially natural experiments in terms of increase and decrease of greenhouse gases, and we can look at how that's affected, how that's recorded in the lithosphere, how the lithospheric feedback and how it's affected the biosphere. So, what is the end result? One scenario here by NOAA, in terms of precipitation, trying to model, hey, it's going to get drier here, it's going to get wetter here. You know, if you have in-laws that live out west, you know, you might want to give them a call, tell them to store some water. So anyhow the impact of global warming, when these are modeled, these are really kind of first order assessments, models. We know from just the most rudimentary examination of the geologic record that when temperatures change on the planet, the climate belts migrate. And that has to do with the way heat is distributed across the globe. But essentially as warming occurs, the polar climate belts will contract, the tropical belts will expand. But it also, this map actually shows the changes per area in warming. So there will be a huge change in the temperature in the north relative to say smaller changes in parts of the Pacific and parts of Antarctica. 

Sea level rise, also as those glaciers melt, sea level will come up, that water has to go somewhere. It pours into the ocean. Sea level will come up. Again, if you have relatives living in the Miami or New Orleans area, you might want to talk to them as well. How fast is this going to happen? Again, we can model that. There's lots of scientists out there doing lots of wonderful work looking at the stability of ice sheets. We have great scientists at the Wisconsin Geological and Natural History Survey who study the glacial deposits of Wisconsin, world class glacial deposits, recording the expansion and contraction of glaciers, especially during the last Wisconsin glaciation that ended about 10,000 years ago, so we can look at modern glaciers, how they're behaving. We can go to the sediment and rock record to try to get an assessment of how they've behaved in the past. And we can go a little bit even further back in time. Recent, now, you know that geologists, when it says 800,000 years, that's pretty recent to me. 

Typically I don't consider things old unless they're a couple hundred million years old. There are several records that we can look at to start to assess how the climate, how the biosphere has changed through time. Carbon 14 you probably heard about in grade school. It's in charcoal. This is used by archeologists and Indiana Jones all the time to date archeological sites. You can date deposits going back about 50,000 years. There are other techniques, speleothems, looking at cave records. One of the best, really, is ice cores for assessing how the hydrosphere, the composition of the atmosphere has changed through time. That record actually goes back to about 800,000 years now. Showing some data here on the bottom of the slide, this is from the ice core drilled in Antarctica. 

There are ice cores from all over the world now. This one is pretty famous. It's got a very interesting record. It beautifully shows these kinds of cycles of rise and fall. Now, this data is represented in degrees Celsius here, so this is essentially temperature. This is a proxy record, though. You can't just take ice out of a glacier and say, hey wow, look, temperature. This is essentially, they're looking at the different isotopes of hydrogen in this case. And we can get into later how do you derive temperature from the relative abundance of one stable isotope of hydrogen over another, but it has to do with the thermodynamics of the evaporation of water, transport of water and you can back calculate out a temperature. So you see these beautiful cycles going back in time, so this is going back 400,000 years, and we're sitting here, okay. 

So you go back in time and it's about the same temperature and then it gets much colder very rapidly, and then it starts to warm, warm, warm, yes, and then it gets much colder rapidly. Or you can go toward the present, which is the typical way a geologist thinks, and you have rapid warming and then slow cooling and expansion of glaciers and then rapid warming and deglaciation, and then rapid-- excuse me, growth of glaciers and cooling. So there are essentially four or five of those cycles represented here. Now, this is context, okay? This is what I was talking about earlier. You say, now here we are today and it's getting warmer. Is that part of the natural cycle? Right? I mean, that's been an argument that people have thrown out there, that, well, it's getting warmer, but sun spot activity changes, and solar insulation, and things like that. This is probably just part of the natural cycle. That's not what this record is saying. And this is, these patterns of warming and cooling, essentially what are known as glacial cycles, they're each about 100,000 years in duration and there's pretty good evidence that this growth and contraction of ice sheets, this cooling and warming, is regulated by changes in solar insulation. Essentially how much of the sun's energy reaches the earth's surface. 

And this is really related-- this is a situation, a scenario, that only as far as we know occurs when you have large ice sheets. So large ice sheets present interact with energy from the sun in such a way that they kind of take over, they hijack global climate, okay? So this warming and cooling, warming and cooling, this is really telling you about the relationship of the earth to the sun, that's what's controlling this, and that's what is causing the expansion and contraction of glaciers. And so we're sitting here today, which way should we be going? Should we be getting warmer or cooler? We're in a warm spot right now. We should be going into the next glaciation. It should be getting colder according to this record, right? If we take the last 400,000 years as the norm, then you see these deglaciation, and warming, and cooling, deglaciation and glacial growth, deglaciation and warming, to here, and now we should be going toward the next glaciation. Instead, we're shooting up this way, okay? We're getting warmer. And in fact we're getting warmer than it's been in the last 400,000 years. So we can't even-- Let me talk about, real quick, about how these records get in the ice. So the hydrogen record comes from the ice itself, okay. So you're essentially looking at the record of water and how the isotopes of hydrogen are changing in the water that's becoming ice. 

Another way to get a temperature is to look at the oxygen isotopes, Oxygen 16 and Oxygen 18 and their ratio, and they tell you, they give you an indication both of how much ice there is globally, but also temperature. This other graph down here in, sorry, parts per million, this is a proxy record for CO2, okay? So you see it matches the temperature record. And so carbon, changes in carbon dioxide are marching along in step over the last 400,000 years with changes in temperature and changes in ice volume. And also remember as that ice expands and contracts, sea level goes up and down. So these are all working in concert. They're happening at the same time. The oxygen isotope and carbon isotope record is coming from gas bubbles that are trapped in the ice. These are little bits of atmosphere that were trapped at the time that that glacier was growing. And glaciers show, I should have a picture of that up here. I'm sorry I don't. 

Glaciers show beautiful banding within them that are annual bands from summer, winter, oscillations. The banding, the visual banding has to do with the density of the ice. If the glacier is growing rapidly, it has low density, it traps a lot of gas. If it's summertime it's growing slowly, it's very dense, and it doesn't have a whole lot of gas. So these records are coming, especially when we're looking at this record, which is the carbon isotope record and carbon dioxide is a proxy from that, or is taken from that. These are coming from gas bubbles, bits of atmosphere that are actually trapped in the ice. You couldn't ask for anything better. It's little samples of what the atmosphere composition was at the time that that glacier was growing. It's a really fantastic record. It gets worse as we go back in time. 

You go back beyond 800,000 years, and there's no more ice record. That's about as old as any glacier gets on earth. If we want to look at much longer periods, right, because I just said we're getting into a time that's warmer than what we've seen over the last 400,000 or 800,000 years. How do we assess based on even that long period of time, what to expect, how the earth is going to change and respond to this warming? There are all these natural experiments in the rock record. We just need to go look for them. So we can look at a longer time period. This is showing the Cenozoic era. That's 65 million years. This goes back to the extinction of the dinosaurs, or the age mammals, you can kind of think of it as. We're looking at two records here. 

These are oxygen. So, again, I said oxygen's a proxy for both ice volume and temperature. This is the oxygen isotope record going back almost 70 million years, just beyond the beginning of the Cenozoic and the carbon isotope record. Again, this is the proxy for carbon dioxide. Now, most or better than half of the Cenozoic Era actually occurred during a time, the last 30 million years, when there were big glaciers on Earth. The Antarctic ice sheet starts to form around 35 million years ago, 38 million years ago. Northern hemisphere ice sheets start to form around 10 million years ago. So, a good bit of this Cenozoic record is a time when we have big ice sheets. But what we're seeing as climate, as global temperature is rapidly increasing, that our ice sheets are destabilizing rapidly, and there may be a time soon when we don't have big ice sheets. So if we want to understand how the climate system operates during a time of ice sheets, this is probably a good time window to look at, the last 30 or so million years. 

If we want to understand how that world functions without ice sheets, we want to go back further and we can look at the earlier Cenozoic, back in this time interval. These records come from the shells of tiny, in some cases, microscopic single celled animals that live on the sea floor. And so they're sampled from rocks of varying ages to generate this record. They're called foraminifera. Again, they're a single cell organism that secretes a calcium carbonate skeleton to live in, essentially. And, again, that's calcium carbonate, it's calcium, carbon and oxygen. So those two records that we want, oxygen, again, this proxy for temperature; and carbon as a proxy for carbon dioxide are basic components of those skeletons. What we see around the onset of the Antarctic ice sheet is a major shift in the oxygen isotopes. And their shift is associated with that locking up of large amounts of oxygen in ice sheets. So if you correct for that, there's actually a lot of agreement between this carbon isotope record, which looks relatively straight and flat compared to the oxygen isotope record. 

So you take out the ice effect and these start to look very similar. And it leaves us with a few questions about how temperature and changes in carbon dioxide operate further back in time. We know from the ice record that carbon dioxide changes during ice house worlds, is what it has typically been called, these times when we have big continental glaciers, ice house worlds. During ice house worlds carbon dioxide levels tend to track changes in temperature. As glaciers expand, they tend to lock up CO2 and when they contract they tend to release CO2, and again that's shown in this curve here. There's a slight offset. It's hard to see. But if you were to overlap those perfectly, you would see the green is slightly shifted more toward the modern. CO2 levels track oxygen. In some of these older records, especially when we start to look at the Cenozoic as a whole, it becomes a little bit more difficult, especially at this scale, to assess what that relationship is. 

Again, so we're looking for proxies on how the world operates and what these lithosphere, biosphere, hydrosphere interactions are in deeper time, especially during greenhouse worlds. There's one really interesting aspect of this carbon record. There's many, but one especially and it's especially pertinent to our discussion here and that is this little thing right here. That's right at the Paleocene-Eocene boundary. So these are divisions of the Cenozoic. Those divisions were made based on the distribution of fossils. Long before we started pulling out chemistry from rocks of this age, paleontologists were looking at these rocks and saying there's a significant difference between the fossils we find in these rocks down here and the rocks just above them. In fact, there's a major extinction of these little foraminifera at that boundary. And what we now know is there's also a very rapid change in the carbon isotope values and we see very light carbon introduced very rapidly. And looking at this and comparing it to the oxygen isotopes, you see a big spike in oxygen isotopes right here. 

So there's a coordinated shift in the carbon and the oxygen here. And what we've been able to sleuth out of this, that is, actually even some scientists working at UW, is that that represents a rapid introduction of light carbon. That carbon is coming from methane. That very light carbon is a signature of methane. Which is kind of a much more potent form of greenhouse gas than carbon dioxide is. And this represents a very rapid warming associated with that. So here we have one example from the Cenozoic of a very rapid warming associated with a release of methane and we're seeing that it was detrimental to life in the ocean as we have this extinction right here. So that leaves us with some questions. We look at the whole Cenozoic, we see evidence for one rapid warming event. How common are these things in the earth's history? Is this something that happens all the time and there's some signal locked away in our DNA, in the DNA of the organisms of the planet to be able to deal with rapid warming, or is this something totally new and different and especially significant? How does the carbon cycle operate under greenhouse conditions? Our best record of how the carbon cycle operates, which, again, we're carbon-based. 

All life on the planet is carbon-based and also those greenhouse gases are carbon-based. So if we want to understand how these interactions occur and better constrain our models, we need a better understanding of the carbon cycle, especially under greenhouse conditions. And then a kind of question that goes along with that is I've had a lot of people say to me, okay, that's fine and all, you want to look beyond the Cenozoic, but isn't the record really incomplete? Isn't there a lot of gaps and stuff in there? Especially as the rocks get older, these 500 million old rocks you like looking at, aren't they really, doesn't the record get worse going back? So we can address that as well. I'm showing here the Grand Canyon as sort of the archetypal image for looking at rock layers as kind of pages of earth's history and trying to unravel that history from looking at those successions. So to bring us around to Wisconsin, the rocks from Wisconsin range from 2.5 billion to 350 million years old, those rocks of the U.P. that were mentioned earlier, the Upper Peninsula of Michigan, are in that range of 2.5 billion years old, an order of magnitude older than these Paleozoic sedimentary rocks which rim the state. So the Paleozoic rocks are around as old as 500 million to about 350 million years old. They wrap around from the Door Peninsula down to the Illinois border and up again into the northwestern portion of the state. They were deposited in a shallow, tropical sea, or several shallow, tropical seas. As you can see, they span an immense time period. 

So they record a period of Earth's history where we have a fossil record, where we can look at relationships of at least organisms that had hard parts that can become fossilized and how they reacted to changes in Earth's climate. So most of these rocks in the Paleozoic of Wisconsin are carbonates, okay, like limestone. I'm sure you're familiar with limestone or dolostone. We have a lot of dolostone in the state. These are the rock equivalent of sediments laid down on the sea floor made up primarily of the hard parts of marine organisms. Those organisms for the most part were secreting their skeletons in equilibrium with sea water. So they're creating skeletons. Where are they getting the material? They're taking it out of the sea water that they live in. So those records, those carbonate rocks, have encapsulated within them the record of ocean and climate change in an ancient part of Earth's history.  Carbon isotope work in particular in these very ancient rocks has undergone kind of a revolution in the last decade. 

Geologists working on the chemistry of these rocks early on were very slow to embrace looking at the carbon isotopes. They were worried about modification of the signals. Were we looking at a robust, repeatable signal? As I'll show you in a minute, it's incredibly robust. The carbon isotope signal is incredibly robust and repeatable both between closely spaced and widely spaced sections. It's a signal that we can pick up globally in rocks of equivalent age. It turns out that we can really do some fantastic work on ancient rocks in terms of trying to look at the carbon cycle utilizing carbon isotopes. So you're probably then saying, well, wait a minute, what are carbon isotopes? So when we're looking at the carbon isotope record, we're really comparing the ratio of carbon 12 to carbon 13 in those rocks. Those are the two stable isotopes of carbon.  So why does that matter, and why does that vary through time? Okay. The way that it varies is that essentially we're looking at two different groups of organisms that are affecting the record of carbon or that proportion of carbon 12 to carbon 13. 

The first of photo synthesizers that live in the ocean, phytoplankton. You probably heard that term before. These are microscopic plants that live typically in the upper few meters of the ocean. They're taking the sun's energy and pulling carbon dioxide out of the air and using the sun's energy to split that and create tissues out of the carbon to grow, to replicate. Think of Madison lakes in the late spring and summertime. Okay? It gets warm. We have an abundance of nutrients. We get algal blooms. These are the same kind of organisms, single celled plants living on the surface of that water and they're getting what they need to grow and they're expanding rapidly. Under normal circumstances you have the biological pump. 

This is a recycling mechanism, okay? So essentially below those algae you have bacteria and other organisms that are metabolizing the dead algae. So as algae lives, reproduces and dies, eventually it rains down into the water column. It's attacked by bacteria, which respire that organic matter, they break down that organic matter, they take energy from it just like we do and they respire CO2 just like we do in the presence of oxygen. So they're pulling oxygen out of the water column. This is why our lakes, we go anoxic to a certain degree and then we see these green blue algae blooms afterwards. It's that the abundance of the algae starts to overwhelm the system. So you have an algal bloom. You have all this organic matter that's being created in the surface. The bacteria are trying to break down all the organics that are coming in and they're using up the oxygen in the water. And when they do that, they shut down the biological pump because they can't exist without oxygen. 

They certainly can't do their jobs without oxygen. So that organic matter now starts to go to the bottom of the lake or the bottom of the ocean in the case of marine systems. And that's how you get global fractionation from carbon 12 to carbon 13. The plants are preferentially taking carbon 12 out of the atmosphere because metabolically it's easier to work with. They don't want the heavy isotope of carbon, carbon 13, so they're leaving it behind. So in the cases where they die and rain down onto the surface, they're taking carbon 12 out of the surface and the world becomes enriched in carbon 13. And this fluctuates back and forth through time. The other group of organisms are those that are biomineralizing, those who are creating hard parts from sea water, okay? So they're pulling calcium and carbon and oxygen out of the sea water to create their shells, their skeletons. In doing so, they are encapsulating, essentially the chemistry of that sea water. That is the record we're going for. 

So one group is causing fractionation. The other is just recording that fractionation through time. And those are the guys that we go after to try and look at changes in the carbon cycle through time. So I'm going to run you through a case study really quickly. I've been looking at these rocks of the Silurian Age, around 440 million years old, across northeastern America. This is a reconstruction of the Silurian world. Geographically it's quite different than today. There's a large continent sitting over the South Pole called Gondwana. It's essentially South America and Africa, Antarctica Australia, etc. And straddling the Equator, you have North America. 

Wisconsin was a wonderful shallow tropical sea. You've got nearby bits of Europe as well as Siberia to the north. The northern part of the world is mostly just a vast ocean. Again, one of the main differences besides the position of the landmasses is that the continents all have these shallow seas. So sea level is much higher than it is today and it's flooding the continents. So I started, after I finished my doctoral studies, the NSF-funded study, to look at the Silurian Age rocks across eastern North America, essentially from the Appalachians, Pennsylvania, Maryland area, to essentially Wisconsin. And the rocks in the east are different than they are here in terms of their lithology, in terms of what rock types are there. They're mostly shale. This is essentially like compressed mud and sandstone and minor components of limestone. They're exposed at the surface in places, and they are penetrated by borings into the subsurface that are housed at the various state Geological Surveys around the eastern U.S. 

And this is just showing where those data points are. There are general kinds of belts where the Silurian rocks are mostly sand over in this area. They're mostly shale through this area, and there's a lot of limestone and associated lithologies in this area. That's telling us during the Silurian, this was a deposital basin. There were deep areas. There were mountains off this way, and this was kind of a catchment area for sediments.  So what I'm showing here is a cross-section. This is across Ohio, essentially from the margin of that basin, the western margin of that basin, going out into the basin interior. These lines represent timelines that are constrained, in part, by the carbon isotope values, which are these profiles here for each one, and then there's a lithologic log or a log of the different rock types that's associated with that. So the study is looking both at the changes in the composition of the rocks, as well as the chemistry of the rocks. 

When you put all that together, you end up with essentially a slice across that basin that looks like this. So this is for a specific part of the Silurian. Again, this is a time about 440 million years ago. This is a basin fill. These are marine rocks. They're full of fossils and things like that. What it's showing us, the take-home message here is that this basin had very little organic carbon deposited in it for several million years, okay? All these red and green colors, these are telling you that you have reduced and oxidized forms of iron present in the rocks, but very little carbon. When you have high carbon level in the rocks, it masks these colors and you get shades of gray to black, okay? And that's indeed what you see up here. So the first thing we notice is we have a change in the lithology and that's reflecting the carbon content. So we have a period, a long period, this initial basin fill, that has very little carbon and then an abrupt change to a lot of carbon being deposited in this basin. 

When we look at the carbon isotope profile, that time of low carbon fill is associated mostly with a time when we had very low carbon isotope values. Essentially it's telling us we're in a greenhouse period. It's warm. There's a lot of carbon dioxide. When the values shift in this direction, we see suddenly that we have lots of organic carbon in the rocks. This is telling us that even if you go back 400+ million years, the carbon cycle essentially was acting the same way as it does today. You take organic matter from the surface ocean and you put it in the bottom and that causes that global ratio of carbon 12 to carbon 13 to shift. That's the take-home right there. The red and green rocks had very little carbon. There was essentially no net flux of photosynthetic light carbon or plant remains, if you want to think of it that way, to the bottom. 

The biologic pump was working, everything was being recycled, there was very little change in that ratio globally of carbon 12 to carbon 13. Suddenly something happened and there was a lot of organic matter made at the surface, it went to the sea floor and continued to do so for a good, long time, and that causes the rocks to turn gray to black, like old graphite in a pencil, it has that gray to black color. That's carbon. It changes the color of the rocks like that. And it also shows a coordinated shift in the carbon isotopes to values that indicate that globally you're having a period of carbon burial. The two reinforce each other. They're telling us that the carbon cycle is working as it does today, essentially. And that's reassuring. The interesting thing is this is associated with one of the largest mass extinctions in that time, in the Silurian time period. So a bunch of organisms go extinct right around that time. 

So that's telling us that, wow, something happened. It changed that carbon cycle dynamic. And that was not a good thing for most life on Earth. It's also associated with a major fall in sea level and some other changes as well that I'll get into in a minute. And, again, this is not just -- these patterns we don't just see in eastern North America, but this is a globally synchronous event. We can look at those same rock records on different continents and we see the same patterns. So just to summarize what our study showed is that these are the carbon isotope values. There's a little blip down here. And we see some things going on with sea level over here, sea level dropping and then rising around the same time. We have some oxygen isotope data as well, which is indicating a shift towards cooler temperatures associated with that little blip. 

The big change that I just showed in that diagram is in this interval, where we see a large shift in the carbon isotopes, a major cooling and evidence actually for glacial deposits in South America, what is today South America, and a big drop in sea level. So this is very similar to what we see in the ice core record. The difference is, and it's a subtle difference, is in the offset between the carbon isotopes and the oxygen isotopes. During the ice house world, the carbon isotopes or carbon dioxide tracks temperature change. So it gets warmer, glaciers contract, you release carbon dioxide. And then the reverse is true as well. In the greenhouse world of the Silurian and as it will turn out other time periods as well, it's just the reverse. Carbon dioxide, changes in carbon dioxide, are forcing changes in temperature, okay? So those greenhouse gases are forcing, in a greenhouse world that's the primary control on temperature, is the flux of greenhouse gases, okay? Increase greenhouse gases, it gets warmer. Decrease them, it gets cooler. There's a pretty direct relationship there. 

To bring it back to Wisconsin, we've got some beautiful data from Wisconsin that matches very well, both that data from over in the Ohio River Valley, as well as kind of what the global curve is. This is for a longer time period, but it's a fantastic tool. Not only does it tell us about the carbon cycle. It's allowing us to align these geologic records from all over the world in a much more accurate way. We've also looked at some older rocks in pretty fine detail, and this is just a quick summary slide to say similar patterns exist in even the older rock, so the Silurian are some of the youngest Paleozoic rocks in Wisconsin. Even the older rocks show similar patterns. There are high frequency patterns. This is a large, in the heavy gray line this is a large shift in the carbon isotope values for some of the older rocks. There's a high frequency signal there as well and there's some really large negative excursions in there. This is still pretty preliminary work, but it looks very similar to the Paleocene-Eocene boundary that I talked about the Cenozoic. 

So we've got some evidence for very rapid warming events in the record as well and we have some volcanic ash beds in there that help us constrain the duration of those things. So kind of to summarize, we're trying to kind of pull together these ancient rock records to get a better sense of how the carbon cycle operates during greenhouse times and what some of the associated phenomena are when you start to really change the flux of greenhouse gases in or out of the hydrosphere. So this is showing essentially, I'm sure you've never seen anything like this before. This is a cross-section from Wisconsin, from essentially Madison to Virginia. And the Y axis here is time. So this is the whole Silurian period from about 440 million years to 415 million years, getting younger towards the top, and these are the rocks that are preserved today. We've just kind of reconstructed them in terms of their different ages. And the take-home message from this reconstruction is every time we get big shifts in the carbon isotopes, we're seeing coordinated shifts in evidence for sea level fluctuation, carbon burial, extinction. They all go hand in hand over and over again. There are multiple, large changes in the carbon cycle and we see that pattern repeatedly. 

We can go to slightly older rocks. These are the Ordovician rocks. So now we're looking at 480 to 440 million years. It's the same pattern over and over again. We can look at even older rocks in Wisconsin. And part of the work is really trying to tie in the fossil record with the carbon isotope record. This is showing the diversity of a planktonic organism. It's not a plant, wasn't an algae, it's long extinct called a graptolite animal. This is the critter up here. Its organic remains are found in a lot of fine grain rocks of order of issue of Silurian age. 

This pattern down here is essentially showing its diversity through time. So these things were kind of prolific during certain times and became very diverse and then their diversity would contract. So we see this kind of long run-up to very high diversity through the early part of the Ordovician, and this really parallels a global trend that we see in the Ordovician that's called the Ordovician radiation. This is one you should teach your grandchildren. This is essentially the diversification of life on the planet as we know it. This is where all the animals came from, okay? You've probably heard of the Cambrian explosion. That's the appearance of a lot of weird things that went extinct pretty fast. The Ordovician radiation is the appearance of all the forms that we essentially see today. Even though not the same species, the major families. So that happens during this time. 

We look at the carbon record and it's pretty quiet. This is actually, this is a greenhouse time and there's not a whole lot going on. When we start to see the carbon isotope record or the fluctuations in carbon dioxide, we can think about it. When we start to see that really vary, that's when this record of graptolites or a proxy for the record of life, really starts to get ragged and we see some very abrupt changes and we can look at this in a different way. This is a plot of extinction intensity. This is from a recent paper in "nature," where essentially the fossil record was plotted against, and that would be here, plotted against time. So this is rocks that are about 550 million years old on this end to the present, and this is how much extinction is going on. And so you see these big spikes. These are essentially mass extinction events. The rocks of Wisconsin, the Paleozoic rocks, occupy about this period of time, and you can see we have multiple major extinction events captured in that rock record. 

And they're all coincident with major changes in the carbon isotope record. So just to wrap it up then, global warming is happening today. Absolutely. It's causing significant environmental and societal changes. To really put it in context, though, we need a clear picture of how climate has changed in the past. Definitely especially for those forward models that we really need a better understanding of the behavior of the carbon cycle, especially under greenhouse conditions. We have these ancient records like in Wisconsin. They show a direct relationship between carbon burial and the carbon isotope pattern. They show direct changes associated with changes in sea level. And there are also these little negative excursions in there as well that look very much like this, the Paleocene-Eocene thermal where they have this very rapid warming. 

Peaks in extinction rates seem to be tied very closely with rapid changes in the carbon cycle and that's ongoing work that we're continuing to focus on. So I thank you for your time. [APPLAUSE]