"What is the most widely accepted theory on how photosynthesis evolved from non-photosynthesis based life?"
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What role did ozone play in the evolution of life on Earth
Earth did not develop an ozone layer in the atmosphere until there was a substantial quantity of oxygen gas available. The Earth's atmosphere became oxygen-rich starting about 2.1 billion years ago, so that is approximately when an ozone layer should have developed. Ozone's main role in biology is to shield the surface from much of the damaging ultraviolet light from the Sun. Before there was ozone, life was restricted to marine environments. Later, life could expand into shallow tidal areas and eventually to land. However, it is interesting to note that the interval between the probable formation of an ozone layer and the proliferation of multi-celled life on land was a very long time -- roughly a billion years. David Morrison
NAI Senior Scientist
November 23, 2007
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