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Effective communication in the geosciences requires a consistent nomenclature for stratigraphic units and, especially, for divisions of geologic time. A geologic time scale is composed of standard stratigraphic divisions based on rock sequences and is calibrated in years.
Geologists from the U.S. Geological Survey (USGS), State geological surveys, academia, and other organizations require a consistent time scale to be used in communicating ages of geologic units in the United States. Many international debates have occurred over names and boundaries of units, and various time scales have been used by the geoscience community.
For consistent usage of time terms, the USGS Geologic Names Committee and the Association of American State Geologists developed the Divisions of Geologic Time; the 2018 update in this fact sheet contains the unit names and boundary age estimates ratified by the International Commission on Stratigraphy in 2018. Scientists may use other published time scales, provided that these are specified and referenced.
U.S. Geological Survey Geologic Names Committee, 2018, Divisions of geologic time—Major chronostratigraphic and geochronologic units: U.S. Geological Survey Fact Sheet 2018–3054, 2 p., https://doi.org/10.3133/fs20183054.
ISSN: 2327-6932 (online)
ISSN: 2327-6916 (print)
Table of Contents
Additional publication details
|Publication Subtype||USGS Numbered Series|
|Title||Divisions of geologic time—Major chronostratigraphic and geochronologic units|
|Series title||Fact Sheet|
|Publisher||U.S. Geological Survey|
|Publisher location||Reston, VA|
|Contributing office(s)||Eastern Geology and Paleoclimate Science Center|
|Online Only (Y/N)||N|
|Additional Online Files (Y/N)||N|