As we think about the history of life on Earth, we now want to note that the history of life is told mostly through fossils. We just want to spend a little bit of time talking about what fossils are and how they're made. So, fossils are defined as the preserved evidence of organisms from the past. Normally, when I think about a fossil, I think of something like a bone. However, here, we're defining them as preserved evidence. It doesn't have to be the organism itself; it can just be something that shows us that the organism was there. Paleontologists study fossils, a fact known even by many children, as at some point many of them want to become paleontologists and dig up dinosaur bones. I know I did.
As we discuss fossils, we categorize them in different ways. Here, we're going to group them into four groups based on how these fossils are made. First, we have fossils made in sedimentary rock, which is normally what comes to mind when thinking about fossils. Sedimentary rock is formed when soil or mud sediment is laid down in layers and compressed to form rock. If an organism is buried in the sediment, it can turn to rock along with that sediment, like the Archaeopteryx we see here. However, that's not the only way fossils are made. Fossils can also be found in amber when tree resin captures entire organisms intact. This process preserves small organisms, such as insects, and can be incredibly valuable.
We also have trace fossils, which are essentially the preserved evidence we talk about. These include things like burrows or footprints. For example, a dinosaur might walk through mud or volcanic ash, and we can later see that footprint and even put our hand in it. Trace fossils can be valuable as they may show something about how the organism lived, which we might not learn just from the structure of its bones.
Our final type are fossils found in ice, frozen soil, or acid bogs, like the baby woolly mammoth found in the tundra in Siberia. When things are fossilized this way, it can be quite valuable because it preserves soft tissue, such as skin, hair, and muscle. Additionally, this allows us to retrieve biomolecules like DNA, which means we could even perform genetics on these fossils. However, the downside is that ice, frozen soil, and acid bogs do not last long in geologic time; environments change, ice melts, and those fossils can be lost. Typically, these conditions preserve remains in the tens of thousands of years, not in the millions or hundreds of millions of years that you can see with other types of fossils. With that, we'll spend more time on fossils coming up. I'll see you there.
