Age (geology)

Units in geochronology and stratigraphy

Segments of rock (strata) in chronostratigraphy	Time spans in geochronology	Notes to geochronological units
Eonothem	Eon	4 total, half a billion years or more
Erathem	Era	10 defined, several hundred million years
System	Period	22 defined, tens to ~one hundred million years
Series	Epoch	tens of millions of years
Stage	Age	millions of years
Chronozone	Chron	subdivision of an age, not used by the ICS timescale

A geologic age is a subdivision of geologic time that divides an epoch into smaller parts. A succession of rock strata laid down in a single age on the geologic timescale is a stage.

See also

• List of geochronologic names