Fossils were once living things that died and became trapped in a layer of sediment. As the layers of sediment built up the pressure increased and the dead animal or plant slowly turned into a fossil. Fossils are normally the hard parts of animals (shells, bones, teeth etc.) and plants because they fossilise comparatively easily and do not rot away so quickly. Occasionally,  in special environments where a sudden deposition of sediment has covered an area very quickly or in peat bogs and tar pits, the soft parts (skin, feathers, fur, tissues, flowers) can be preserved. Fossils tell us about what animals and plants looked like in the past and help us to study evolution.

Fossils are usually found as isolated specimens in a rock but occasionally there can be many fossils in one rock specimen. Some rocks, such as some types of limestone, are made up entirely of fossils. Fossils are usually found in sedimentary rocks where layers of sediment have encased the dead plant or animal; they are rare in igneous rocks as the heat of the molten rock usually burns up any organic remains, and are very rare in metamorphic rocks as the recrystallisation process usually causes any fossils to be destroyed.

Want to know how to identify a fossil? Click here.