And welcome to Our Earth, Its Climate, History, and Processes. My name is David Schultz. In this lecture, we're going to talk about fossils. This is necessary in order to understand some of the material that we'll be talking about later, specifically the evolution of life throughout geologic history. So, before we get started, remember the basic time scale that we're talking about here. The Earth formed 4.5 billion years ago, and within a billion years, we had the first water-lain sediments, so we know that there was an ocean around. And the, this ocean was producing sediments, and within these sediments are recorded the first fossils. These are likely cyanobacteria. So, with that introduction, let's talk about the three different types of fossils. The first type of fossil is what's called a body fossil. This is a fossil that represents an actual body of part of animal or the complete animal that's left behind and then becomes fossilized. In this case here, we're looking at the skeleton of Gorgosaurus at the Manchester Museum, and what you're seeing are the bones of this animal. Well, actually you're seeing the cast of the animal because mounting these bones would be an incredible task, but the actual bones that made up this cast are classified as body fossils. Here's another type of body fossil. In this case, you get the complete specimen. You get a spider and the fly both preserved in fossil resin or, or amber, and this instance here, which happens to be 100 million years old, but you can see the entire body of these animals preserved. So, those are body fossils. You may also see examples of shells, of brachiopods, corals, whatever. Those are all body fossils. The second type of fossil is a trace fossil. Here we're talking about characteristics that are left behind in the sediment that indicate that the animal was present. In this case, it's a footprint that is preserved in the sediment. The sediment then solidifies, becomes a rock, and then is exposed as it is here in Dinosaur State Park, revealing these fossil footprints. Here's another type of trace fossil. These are different types of burrows by worms or other kind of burrowing animals that then become filled with a different type of sediment and then are preserved. Here's yet another type of trace fossil. Can you see it? Here are three different examples of brittle stars, starfish that have nestled down into the sediment and then those impressions have been left behind. Can you see them still? There's the most prominent one right there. Now, this sample was collected on the Yorkshire coast of England, and there is another type of trace fossil there as well. If you look carefully, you can see yet another trace fossil on this same bedding plane. These indentations in the sand were created by the tube feet of the starfish as it traveled across this bedding plane to its eventual position in the center part of the photo. And finally, the third type of fossil is called a chemical fossil. You may also see it referred to as a chemofossil or a biomarker. The chemical fossil is the existence of molecules in the sediment that indicate the existence of the living organism. On the right is a false color image produced by a rapid scanning x-ray fluorescent instrument, and here, what we're doing is looking for signals produced by the x-rays indicating the presence of different elements. These different elements appear in different concentrations on this fossil. So for instance, there's a lot of zinc in the background information and so that area here has been colored in green. You can see the skeleton, the beak, of the animal, and that is high in calcium, and it's colored blue. And finally, you see the presence of copper in many of the feathers, and the presence of this copper is an indication of the eumelanin molecule, which would represent a dark pigment on these feathers of this bird. So, these elements are buried with the bird, become fossilized, and of course those molecules don't just disappear when the animal becomes fossilized. It's actually still in the rock. And the presence of those elements indicates something about not only the chemical composition of the feathers, but about its pigment. And eumelanin is a dark pigment. It's in people's hair that have dark brown or black hair. So, by mapping the locations on the body where these copper-rich feathers, these eumelanin-rich feathers, were found, the dark feathers, the authors were able to reconstruct then the plumage color of the bird. The dark body feathers were indicated near the body and on the head, and lighter colored feathers where the copper was absent in the feathers in the fossil. There was not that much copper present there, so the, these tended to be lighter colored feathers. So, to summarize today's lecture, we talked about the three different types of fossils, the body fossils, the trace fossils, and the chemical fossils. So, we will put these terms to use as we start discussing how life evolved on Earth.
