Geologic Eon

An eon is the largest geochronologic time unit in the geologic time scale and is equivalent to a chronostratigraphic eonothem. The cited article, Geologic time scale, which also defines the other three ranks because their own titles redirect to it, says there are four formally defined eons: the Hadean, Archean, Proterozoic and Phanerozoic. It shows the whole of Earth history on a first timeline and then gives the most recent eon its own expanded timeline, noting that the previous three eons collectively span far more time than the Phanerozoic. The time scale as a whole divides geologic time into standardised intervals using the rock record and geochronology techniques such as radiometric dating. Time units of this rank in the atlas are grouped under this entry.