T he geologic time scale (GTS) is a system of chronological measurement that relates stratigraphy to time, and is used bygeologists, paleontologists, and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth's history. The table of geologic time spans presented here agrees with the dates and nomenclature set forth by theInternational Commission on Stratigraphy standard color codes of the International Commission on Stratigraphy.
Evidence from radiometric dating indicates that the Earth is about 4.54 billion years old. The geology or deep time of Earth's past has been organized into various units according to events which took place in each period. Different spans of time on the GTS are usually delimited by changes in the composition of strata which correspond to them, indicating major geological or paleontological events, such as mass extinctions.
Geological time, Understanding of Earth history,
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