Radiometric dating kids
Groundwater seeps into the newly made stone and dissolves the bone, leaving behind a mold.
The mold is an empty cavity, and can be filled with minerals that become a cast for the long dissolved bone.
While they didn't have exact dates for how old these strata were, they could determine which fossils were older than others based on which layer they were found in.
Though there is no one age, a good rule is anything over 10,000 years old can be considered a fossil.
The oldest fossils ever discovered are more than 3.5 billion years old.
Fossils are the remains of animals or plants that lived a long time ago.
When we think of fossils, the first things that come to mind are the bones of dinosaurs; but a fossil can be anything.