<P> The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time . It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history . The tables of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS). </P> <P> The primary defined divisions of time are eons, in sequence the Hadean, the Archean, the Proterozoic and the Phanerozoic . The first three of these can be referred to collectively as the Precambrian supereon . Eons are divided into eras, which are in turn divided into periods, epochs and ages . </P> <P> The following four timelines show the geologic time scale . The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon . Therefore, the second timeline shows an expanded view of the most recent eon . In a similar way, the most recent era is expanded in the third timeline, and the most recent period is expanded in the fourth timeline . </P>

What unit of geologic time is the greatest span of time