Fossil clams

A rock with many fossil clam shells. As a rule, after death, organisms are quickly decomposed completely, leaving no trace of their existence. In the rare instances when this does not happen, their remains, as well as some traces of their activity, turn into fossils. Not all parts that make up an organism, however, have the same chance to be preserved in the fossil record: "hard" parts such as shells, bones and teeth, trunks and seeds are more easily preserved, whereas "soft" parts, like skin, muscles and leaves decompose more quickly.