Relative dating is the kind of geochronology that determines the relative order of past events. The idea is to find the age of an object or event by comparing it to another object or event, or by using clues from the environment or circumstances where it was found. Relative dating is not about finding the absolute age. In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another. Before the discovery of radiometric dating in the early 20th century, archaeologists and geologists used relative dating to determine ages of materials. 