Category
page 1Geologic time scales
geologic time scale
a system of chronological dating that classifies geological strata (stratigraphy) in time
eon
subdivision of geological time; short than a supereon and longer than an era
stage
unit in chronostratigraphy
series
sequence of rock depositions defining a chronostratigraphic unit corresponding to a specific epoch on the geologic time scale
chronozone
A chronozone or chron is a unit in chronostratigraphy, defined by events such as
geomagnetic reversals (magnetozones), or based on the presence of specific fossils (biozone or biochronozone).
According to the International Commission on Stratigraphy, the term "chronozone" refers to the rocks formed during a particular time period, while "chron" refers to that time period.
erathem
In stratigraphy, paleontology, geology, and geobiology, an erathem is the total stratigraphic unit deposited during a certain corresponding span of time during an era in the geologic timescale.
system
idealized composite unit of the geologic record representing the totality of rock strata laid down during a certain period of the geologic time scale

eonothem
thumb|200px|right|Horseshoe Canyon Formations exposed in Horseshoe Canyon (Alberta)|Horseshoe Canyon near [[Drumheller, Alberta.]]
thumb|200px|right|Oxfordian (Upper Jurassic) cyclic sediments at Péry-Reuchenette, near Tavannes, kanton Bern, Switzerland. Alternating layers are limestone (light, more competent) and [[marl/clay; dominant cycle is the 200000 year-cycle.]]