Antarctic Microbes Hold Clue to Earth's Oxygen

It wasn't until about 2.4 billion years ago that oxygen filled Earth's primordial atmosphere for the first time, in what scientists call the Great Oxidation Event. The oxidation of Earth's atmosphere and oceans, evidence of which has been seen in ancient rocks, is the biggest chemical change on the surface of the Earth that scientists have ever detected, said Dawn Sumner, a geobiologist at the University of California, Davis. Prior research suggests this spike in oxygen levels was probably due t