The study of the Earth from the beginning of time to the present has been the task of geologists who attempt to unravel the events that have shaped our planet as it is today.
The Earth carries the history of geological events in its rock layers. It follows that the oldest layers are at the bottom and the youngest are at the top. With this understanding geologists are able to determine the ages of rock relative to one another. By assembling all these layers together, scientists have worked out what is known as the stratigraphic column or record of the various ages of rock.
Source:LiveScience
Source: http://www.livescience.com/54518-eras-of-time-since-the-beginning-infographic.html
