Step-by-step explanation:
rock and fossils are made by layers of dirt, sand,organic matter that has beem compressed over thousands,if not millions of years.
some scientists use this layering to determine how old the earth is.
its kind of like looking at the rings of a tree to see how old it is.
the scientists look at each layer of the rock or fossil and use what they already know about when this type of soil or organic matter existed and try to piece together the past