Image: Evolution and Oxygen
of life on Earth as related to the appearance of oxygen in the atmosphere.
The plot of oxygen versus time is modeled after the data of Rye and
Holland (1999), who have proposed this pattern as the most likely based on
studies of ancient soils (paleosols). The
pictures of organisms are meant to emphasize that the early Earth was colonized
by simple organisms, probably <!g>prokaryotic in nature, and that complex organisms
(multicellular large creatures) did not appear until the oxygen levels were near
to what they are now, approximately 500 million years ago.
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