The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history. The time scale was developed through the study of physical rock layers and relationships as well as the times when different organisms appeared, evolved, and became extinct through the study of fossilized remains and imprints. The table of geologic time spans, presented here, agrees with the nomenclature, dates, and standard color codes set forth by the International Commission on Stratigraphy (ICS).
