Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages. Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often the rocks associated with it.Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages. Absolute dating

How are fossils useful in dating?

Geologists get a wide range of information from fossils. They help us to understand evolution and life in general; they provide critical information for understanding depositional environments and changes in Earths climate; and, of course, they can be used to date rocks.