The Archean Eon was a time in Earth's history from about 3.8 billion years ago to about 2.5 billion years ago. It followed the Hadean Eon and preceded the Proterozoic Eon. This was the time when the continents formed. The oldest rocks we can find at the surface are from the Archean Eon. Also during this time life seems to have first appeared. (Life appeared sometime before 3.5 billion years ago, which puts Life's origins in the late Hadean or early Archean. Presumably for most of the Hadean Earth was lifeless, while life existed throughout most, if not all, of the Archean Eon.) It is possible that in the early Archean the entire planet's surface was covered by ocean, although this is really speculation based on the type of rocks that have been found and theories about how the continents originally formed.

1. The page about the Archaean Eon at the University of California in Berkeley.
2. Lecture notes about the Archean provided by Dr. Kevin P. Hefferan.
3. The Smithsonian Institute's page about the Archean Eon.
4. The Paleos page about the Archean Eon.

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This work by Eric & Chun-Chih Hadley-Ives is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.