Curriculum Article

Evolution: Education and Outreach

, Volume 3, Issue 2, pp 198-205

First online:

How Old is Earth, and How Do We Know?

  • Robert M. HazenAffiliated withGeophysical laboratory, Carnegie Institution of Washington Email author 

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Earth scientists have devised many complementary and consistent techniques to estimate the ages of geologic events. Annually deposited layers of sediments or ice document hundreds of thousands of years of continuous Earth history. Gradual rates of mountain building, erosion of mountains, and the motions of tectonic plates imply hundreds of millions of years of change. Radiometric dating, which relies on the predictable decay of radioactive isotopes of carbon, uranium, potassium, and other elements, provides accurate age estimates for events back to the formation of Earth more than 4.5 billion years ago. These and other dating techniques are mutually consistent and underscore the reality of “deep time” in Earth history.


Geochronology Dendrochronology Varves Radiometric dating Carbon-14 dating Uranium-lead dating Prechronism Created antiquity Deep time