Forms of relative dating
Not only did the rock layers indicate changing environments they also revealed that different life forms have existed in different times.
Once Steno recognized that the fossils he was contemplating (sharks teeth and sea shells) were formed in the sediments of oceans he was able to work out the basic rules of stratigraphy.
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 uses the principles or laws of stratigraphy to order sequences of rock strata.
Relative dating not only determines which layers are older or younger, but also gives insight into the paleoenvironments that formed the particular sequence of rock.