Oxygen first accumulated in the Earth’s atmosphere about 2.4 billion years ago, during the Great Oxidation Event. A long-standing puzzle has been that geologic clues suggest early bacteria were photosynthesizing and pumping out oxygen hundreds of millions of years before then. Where was it all going?
Click here for original story, Volcanic activity and changes in Earth’s mantle were key to rise of atmospheric oxygen
Source: Phys.org