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Divisions of geologic time (Bookmark)

March 27, 2020


This bookmark presents information that is widely sought by educators and students. This bookmark is adapted from the more detailed U.S. Geological Survey Fact Sheet 2018–3054, “Divisions of Geologic Time,” prepared by the U.S. Geological Survey Geologic Names Committee in cooperation with the Association of American State Geologists. The fact sheet and the bookmark contain names of geologic time periods and boundary age estimates ratified by the International Commission on Stratigraphy in 2018.