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The Rains Reign4200 Million Years Ago
As Earth cools, water in the atmosphere condenses: torrential rains fall on, and on, and on. Great seas form. Exuberant volcanoes expel hotly agitated deep earth to the surface.
The hot, early atmosphere dances with an abundance of carbon dioxide, nitrogen, and water and lesser amounts of methane and ammonia. Intense energy sources available on the primitive Earth form biologically important molecules from these gases. Candidate sources include solar UV radiation (there is as yet no UV-protective ozone shield), radioactivity, and hot oceanic vents.
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(Bottom photograph courtesy National Center for Atmospheric Research) |
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