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What is geologic time?

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Welcome to CoreFacts, where we're always short on time and big on science. I'm Jessica Robertson. Today's question is...

What is geologic time?

Geologic time is the period of time extending from the formation of the earth to the present. Many international debates have occurred over names and boundaries of units, and various time scales have been used by the geoscience community. Since the mid-1990s, scientists from the USGS, State geological surveys, academia, and other organizations have sought a consistent time scale to be used in communicating ages of geologic units in the U.S. For consistency purposes, the USGS Geologic Names Committee and the Association of American State Geologists developed Divisions of Geologic Time.

For more information about the various eras and the Divisions of Geologic Time, visit

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