Changes

: Most [[animal]] [[fossil]]s come from the [[bone]]s, [[teeth]] and [[shell]]s shells of [[animal]]s which have been trapped under layers of [[sedimentary]] [[rock]]. While there the biological material has been gradually replaced by [[mineral]]s turning it into [[rock]] over millions of years.: Some [[fossil]]s are made when [[organism]]s become trapped in an [[anoxic]] environment where they cannot [[decay]] such as within [[amber]], [[Tar Pit|tar pits]] or under layers of [[ice]].