The Archean Eon

Archaean Landscape; image from Space Biology - source, NASA.

The Archean (or Archaean; formerly Archeozoic or Archaeozoic) was a long and, due to its great distance in time, poorly known geologic eon that last a whopping 1.3 gigayears (or 13 geons). That's almost two and half times the entire history of complex life on Earth. Yet a lot was happening at this time; the origin and growth of continents, and the diversification of life (which may or may not have appeared as early as the preceding Hadean). For this entire time span, and for much of the following Proterozoic Eon, the highest form of life on Earth were algae mats, which sometimes formed dome like structures called stromatolites. These are shown somewhat fancifully in the illustration above, in fact the stromatolites would have actually been under several meters of water; the lack of oxygen and hence of a protective ozone layer in the Precambrian atmosphere meant that the sun's rays would be deadly to any unprotected life.

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