Relative dating geologic events
To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.
Pretty obvious that the dike came after the rocks it cuts through, right?With absolute age dating, you get a real age in actual years.Relative age dating also means paying attention to crosscutting relationships.Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
In a way this field, called geochronology, is some of the purest detective work earth scientists do.There are two basic approaches: relative age dating, and absolute age dating.