GEOLOGY

Detailed explanation-1: -An eon is the largest (formal) geochronologic time unit and is the equivalent of a chronostratigraphic eonothem. As of April 2022 there are three formally defined eons/eonothems: the Archean, Proterozoic, and Phanerozoic.

Detailed explanation-2: -Periods of geological time are subdivided into epochs. In turn, epochs are divided into even narrower units of time called ages.

Detailed explanation-3: -The geologic time scale is divided into (from longest to shortest): eons, eras, periods, epochs and ages.

Detailed explanation-4: -The geologic time scale divides up the history of the earth based on life-forms that have existed during specific times since the creation of the planet. These divisions are called geochronologic units (geo: rock, chronology: time).

Detailed explanation-5: -The oldest subdivision of the time scale is the Precambrian (symbolized by PC, X, Y, or Z in the GRI GIS data). The Precambrian is split into three eons: Hadean (4600-4000 MYA), Archean (4000-2500 MYA), and Proterozoic (2500-541 MYA).