Life existed in the oceans for hundreds of millions of years while the Earth's air was not fit to breathe, research suggested today. Dr Linda Godfrey and Dr Paul Falkowski, of Rutgers University in New Brunswick, New Jersey, found chemical evidence of nitrogen cycles that could not have taken place without the presence of free oxygen.
Nitrogen cycles relate to the way living things obtain and use nitrogen to produce complex organic molecules. Evidence of nitrogen cycles provides a 'fingerprint' of life. The researchers, concluded that organisms which produced oxygen as a by-product of photosynthesis must have evolved by around 2.5 billion years ago.
Full Story: Daily Mail