So in Geology, Precipitation of rock layers took place over the last hundreds of millions of years...During that process many living organisms have died and are precipitated with the rock layers... Let me explain with an example.
Dinasours went extinct Million years ago while the Dodo bird went extinct a couple of hundred years ago
Would you expect to find Dinasour fossils in newer rock layers or the dodo? lets's say 200m deep? Dodo for sure, Dinasour fossils are waay too old to be found at such shallow deeps that's why fossils in newer layer of rocks are absolutely younger than fossils found at deeper layers
