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
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
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
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