What is a Fossil?

When an animal dies most of the time the animal slowly decomposes and breaks down and decomposes. Fossilization is a special process where an animal needs to die in or near a body of water. Slowly, from the water mud, rocks, and sand settle on the top of the dead organism. This creates pressure and force on top of the body. Over millions of years sediment covers the organism’s skeleton, putting tons of pressure and weight on it. Minerals dissolve and seep into the skeleton turning it to stone.  This is the main way of fossilization. There are 4 main types of fossils; body fossils, trace fossils, cast and mold fossils, and ice fossils.

Body Fossils

Body fossils are fossils of preserved remains of the original organism. Bones, shells, teeth, wood, and exoskeletons are examples of body fossils. These parts of organisms are less likely to succumb to decay and weathering. Body fossils give paleontologists firsthand evidence on what the organism’s size, shape, and anatomy was. Occasionally though, but very rarely, the soft parts of organisms are preserved. Skin, tissue, organs, leaves, flowers, fruits, and seeds are some of many types of soft body parts. There have been many, rare, instances where the skin and skin cells were so closely preserved scientists know almost everything about them. The best example of this is an almost perfectly preserved Edmontosaurus named Dakota. Scientists say Dakota shouldn’t even be possible with its skin that was preserved for that long.

Trace fossils

Trace fossils are evidence of organisms’ whereabouts such as footprints, coprolites, and burrows. These help show paleontologists if they were solitary or herd animals, the organisms diet, and how they formed their homes. Trace fossils help form paleontologists’ understanding of prehistoric life. For example with recent evidence paleontologists know that the dinosaur Maiasaura lived in giant herds of thousands of individuals. 

Cast and Mold Fossils

Mold fossils are fossils that are a hollow impression of a past organism. This includes shells, bones, or leaves that decayed but left behind a mold of itself. Mold fossils are very similar to body fossils, they give the same evidence but they are two completely different types of fossils. Mold fossils are formed when sediment, mud, or ash covered a dead organism but it still decades leaving a hardened, negative expression of the animal or plant that was once there. A cast fossil, in some cases, is the step after a mold fossil is formed where after the mold of the organism is hardened different sediment or minerals fill the mold leaving a positive expression of the organism. It works the same as a body fossil but instead of it being the actual organism it’s a cast of what the organism was. 

Ice fossils

Ice fossils are the most valuable of fossils to scientists but they are formed millions of years after every other type of fossil. Ice fossils were formed during the ice age, a period of time where the entire earth went into a global freeze whereas body fossils, Trace fossils, and cast and mold fossils were formed in a completely different time period with a completely different environment. Ice fossils perfectly preserve organisms, freezing them in time. Their organs, skin, brains, bones, hair, and other parts are so frozen in time you get to look at the actual organism, not a mineralized version of it.