http://news.ku.dk/all_news/2013/2013.9/earth-history-to-be-rewritten/ " OXYGEN Until now, science has believed that oxygen in the Earth's atmosphere has been around for roughly 2.3 billion years, or roughly half way back along our planet's 4.6 billion year timeline. However, new research results provide evidence that the dating of a so-called “Great Oxygenation Event” needs a 700- million-year backwards recalibration. The dramatic results come from a project involving researchers from the University of Copenhagen (UCPH), the Nordic Center for Earth Evolution (nordCEE), the University of Southern Denmark and several other universities globally. The incredible discovery suggests that the history of life on Earth now includes a previously unrecognised chapter. The results are now published in the renowned scientific journal, Nature. "