geologic time scale

1. n. [Geology]
A chronological chart of the stages and ages of events in the history of the Earth, from its initial formation to present, that has been constructed on the basis of the rock record. As is the typical natural position of rocks, the oldest event is at the bottom of the chart and the youngest is at the top. Both absolute and relative ages of rocks and fossils supplement interpretations from rocks. The vastness of geologic time and the slowness of geological processes are difficult to capture in a simple chart.