In geochronology, an epoch is a subdivision of the geologic timescale that is longer than an age but shorter than a period. The current epoch is the Holocene Epoch of the Quaternary Period. Rock layers deposited during an epoch are called a series. Series are subdivisions of the stratigraphic column that, like epochs, are subdivisions of the geologic timescale. Like other geochronological divisions, epochs are normally separated by significant changes in the rock layers to which they correspond.
Epochs are most commonly used for the younger Cenozoic Era, where a greater collection of fossils has been found and paleontologists have more detailed knowledge of the events that occurred during those times. They are less commonly referred to for the other eras and eons, since less fossil evidence exists that allows us to form a clearer view of those time periods.
List is ordered from youngest to oldest and subdivided based on era and period. Certain periods, notably those in the Mesozoic are divided into Early, Middle and Late epochs, with the corresponding stratigraphic 'series' named as Lower, Middle and Upper.
(Note that there are differences in the rank traditionally accorded to divisions of the Carboniferous between Europe and North America.)
Geochronology: From largest to smallest: