The geologic time scale (GTS) is a system used by Earth scientists to organize the timing of events in Earth’s history. The largest defined unit is the supereon, which is composed of eons. Eons are divided into eras, which are further divided into periods, epochs and ages. Because there is a relationship between these time frames and the Earth’s layers of rock, there are corresponding terms (eonothem, erathem, system, series, and stage) that refer to the matching layers of rock.
