Examples of relative dating and absolute dating
Locally, physical characteristics of rocks can be compared and correlated.
On a larger scale, even between continents, fossil evidence can help in correlating rock layers.
This would also mean that fossils found in the deepest layer of rocks in an area would represent the oldest forms of life in that particular rock formation.
Scientific measurements such as radiometric dating use the natural radioactivity of certain elements found in rocks to help determine their age.Scientists also use direct evidence from observations of the rock layers themselves to help determine the relative age of rock layers.