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12. The Permian.docx

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University of Toronto Mississauga
Jessica Hawthorn

The exam will cover everything we’ve talked about since the last exam. You’ll have the same number of questions in the same format. Make sure you bring a pencil, NOT a pen. You’ll take the exam at noon. The marks will be up by two or three. This should give you enough time to make a decision about dropping the course. Today, we’ll talk about the Carboniferous, the Permian, and maybe a little bit of the Triassic. The Permian, which lasted from 290-248 million years ago, ends with the biggest extinction in earth’s history. We’ve estimated that 98% of all species went extinct at the end of the Permian. It’s probably more like 95%. In the carboniferous...well, around the very end of the Devonian and the beginning of the Carboniferous, we have the evolution of gymnosperms. These are the groups of plants which become pine trees and conifers. Ferns are one of the dominant groups of plants at this time. They are very abundant. The lycopods are giant club mosses that look like trees but are actually an example of convergent evolution. They form entire forests. Why do we care about the forests? The forests in the carboniferous go onto form the coal that has driven a large part of the North American economy for the last 100 years. When we burn coal to generate energy, we are burning the carbonized remains of coal swamps deposited during the carboniferous. Coal is basically carbon. It is a form of low-grade metamorphosed carbon. It is organic material, plant material that has been buried, and then subject to heat and pressure. Where does this happen, and how? Where we get these coal swamps is on what was then the edge of exposed land during the carboniferous. This was the stretch of land running from West Virginia and Pennsylvania to the shoreline of Alberta. There was a series of swamps and deltas. As sea levels rose, water encroached onto the land. It drowned these terrestrial environments. Hence, the swamps got buried. Subsequently, sea levels fell, and new swamps grew on top, and, after a certain period of time, sea levels rose again, thus burying the swamps. This cycle went on constantly. We got these repeating cycles called cyclothems. Sea levels go up during transgression and fall during regression. Can anyone give an example of what phenomenon would lower sea levels? Glaciation. Who there is increased polar ice, water is locked up in the form of ice. Conversely, when you melt polar ice, sea levels rise. Right now, we’re initiating a transgression through human activity. Florida is going to be under water eventually. Anyway, we have cyclothems, as a result of which a repeated series of rocks form. These formations follow all of Steno’s principles, and particularly Steno’s second principle. That is, the oldest rocks are on the bottom. The sequence of rocks looks like this. You have non-marine under-clay, then sediments that represent swamps, then marine sandstones, and finally marine limestone. Remember depositional environments. A depositional environment is the place where sediments are deposited to eventually become rocks through lithification. You can look at a sedimentary rock and it can tell you where the rock came from. A particular type of rock represents a particular type of environment. Lime stone represents shallow ocean environments. We have a layer of clay sitting on swamp, which is sitting on top of sandstone (very shallow, almost beach-like environment), which is seated on top of limestone (shallow marine environment). This shows a shallowing of ocean environments from lime to sand, to swamps, to clay. It essentially shows regression. As you go from marine limestone to sandstone, it means the water level is falling. The point is that these cyclothems are repeated transgressive/regressive cycles. Now, Deltas are points where rivers come to meet the ocean. The two rivers go to the ocean. The little islands is the interface between the oceans and terrestrial environments. What happens when the sea levels rise is that the land gets flooded. The ocean shore moves to the right (in the picture). As it rises, it buries terrestrial environments. Sediments from the sea are deposited on top of that swamp. You thus end up with a coal layer. The under-clay, the thick black bar, that stuff gets deposited as sea levels rises. It buries the swamps. Then, it falls. It exposes land, forests grow on the land, and you get swamps again. Then, you have another transgression, and it buries this organic material. We have this cycle of falling and rising. Repeatedly, swamps come into being, are drowned and buried, and then forests/swamps are formed again, buried, and so on. This produces tons and tons of coal. What is it particularly that’s forming coal? The lycopsids. These are giant club mosses 30-50 feet tall. They’re the independent evolution of the tree shape, but they’re not trees. Now, you bury those forests. What does that do to the carbon in the forests? The carbon cannot go into the atmosphere. It gets locked up. It is buried. Basically, between 320 million years ago or a little less, what you have is carbon being pulled out of the atmosphere through photosynthesis by these club mosses. The carbon is locked up between 323 and 290 million years th ago. In the 20 century, it’s burned up RAPIDLY by our manmade technologies. We’re reintroducing carbon into the atmosphere which has been locked up since 290 million years ago. At the same time, we’re not pulled any carbon dioxide out of the atmosphere at the same rate that we’re putting it in. The other thing happening during the Pennsylvanian is you have the first reptiles. Then, we have the Permian. The Permian starts with the continued formation of Pangea. Remember, plate tectonics is occurring. Continents are being formed and destroyed. You have the continuation of the formation of pangea. You form ice at the south pole. At the very end of the Permian, it is the rapid melting of ice, maybe, which results in the greatest mass extinction in history. What we’re looking at here is a distribution of ice and mountains during the Permian. Modern Africa today used to be sitting on the eastern seaboard of North America. Morocco was connected to New Jersey. The North American continental land mass was on the equator, and was hooked onto Africa. How many people in this room liked dinosaurs as little kids? Everybody. We talked about amniotes, which are reptiles and mammals, alligators, us...we are all amniotes. We’re more closely related to each other than we are to amphibians or fish. You have an alligator, a fish, a frog, and you. You and the alligator are more closely related to each other than you are to the tuna or fish. The lineage that leads to mammals is as old as the one that leads to reptiles. We have a common ancestor. At some time, the lineage that leads to reptiles diverged from the common ancestor, and at teh same time, the lineage leading to mammals also diverged from that same common ancestor. You’re more closely related to dimetrodon (a type of dinosaur) then either of you is to an alligator or snake. It was previously called a mammal like reptile. It belongs to a group that includes mammals. That group is called synapsids. Dimetrodon is on the evolutionary lineage that leads to us. Syanpsids have a big radiation during the Permian. There are many of them. We can look at their evolution. Remember, we talked about the evolution of horses. Horses get bigger through time. We also talked about the fossil record of whales. What we have is a fossil record leading to us. The evolution of almost all the anatomic features is included. Everybody here can hear my voice. This is because I’m generating sound waves through my larynx, and the
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