"Earth took its first breath of oxygen 50 to 100 million years earlier than previously thought, suggesting our planet and the life on it "co-evolved," new studies claim.

The two studies reveal that small amounts of oxygen were present in the oceans and possibly in the atmosphere around 2.5 billion years ago, indicating possibly that oxygen-producing microbes, such as cyanobacteria, were already pumping out this lung-filling ingredient, the researchers say. "

http://www.livescience.com/environment/070927_earth_oxygen.html

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