When they die, changesdissolveevidencehardrockSedimentshapespecies parts of the animal don't decay easily. changesdissolveevidencehardrockSedimentshapespecies collects around the dead animals and they become buried.
The sediment surrounding the animal remains also turns to changesdissolveevidencehardrockSedimentshapespecies, but the fossil stays distinct inside the rock.
Over a long period of time the hard parts changesdissolveevidencehardrockSedimentshapespecies and are replaced by minerals. A hard rock-like substance is formed in the same changesdissolveevidencehardrockSedimentshapespecies as the original hard part known as a fossil.
Fossils formed in this way usually develop from hard parts of animals such as shells, teeth and bones.
Scientists can look at the small changesdissolveevidencehardrockSedimentshapespecies that have happened to changesdissolveevidencehardrockSedimentshapespecies of animals over long periods of time by examining the fossils. They can see how one animal has changed. This is changesdissolveevidencehardrockSedimentshapespecies for the theory of evolution.