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When oxygen appeared in atmosphere? |
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Answer» Most scientists believe that for HALF of EARTH's 4.6-billion-year history, the atmosphere CONTAINED ALMOST no oxygen. Cyanobacteria or blue-green algae became the first microbes to produce oxygen by photosynthesis, perhaps as long ago as 3.5 billion years ago and certainly by 2.7 billion years ago. Hope it's helpful |
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