Fossils are our window into the past. They allow us to learn about extinct life, and ecosystems. But there is also a lot to learn about how living organisms become fossils in the first place. The study of the fossilisation process is called taphonomy. This process includes everything that happens to an organism after death. Not every organism becomes a fossil; in fact, it is quite unusual because fossils only form under a particular set of conditions. Especially rare, is the preservation of soft parts, but these can be very useful.
Generally, organisms that live in, or near, water are more likely to be preserved as fossils than organisms that live on land. This is because more rock formed under water than on land. The land is generally a place of destruction through weathering and erosion; dead organisms are destroyed here, not preserved.
Next: Fossil soft parts