a fossil can also be remains of bone shells skeletons or other body parts

a fossil is a hardened remains or other evidence of a living thing that lived a long time ago

fossils are made by a chemical process that happens over time, where an animals tissue is replaced by minerals

because animals decompose fast only a few are preserved as fossils

fossils are found most frequently in sedimentary rock made of clay mud or silt

sediment can build up in many ways EX: wind can blow a thick layer of sand onto dunes

it can also form when muddy water stands still for a long time so the dirrty settles at he bottom

over time the sediment can compact and animals can be trapped in the sediment

but earthquakes can shift or even turn the fossil upside down so it's not always accurate

the fossils that are lower down are normally older becuse the sediment settled there first then other fossils where created later

by studying fossils paleontologists can see how animals evolved over the years

paleontologist studies extinct organisms

fossils show the first vertebrates to live on earth where fishes

the more decayed form of the element the older the fossil

some contain radioactive elements that decay at or change over a known period of time

they use fossils to determine the likely course of evolution the vertebrates have taken

fish appeared on earth 530 million years ago

birds where the latest to appear only 150 million years ago

mammals first lived on this earth 220 million years ago

birds and mammals are descendants from reptiles

320 million years ago amphibians gave rise to reptiles