Geologists revisit Earth's Great Oxygenation Event: More like the 'Great Redox Evolution'

Recent work with geochemical proxies for oxygen levels suggests that oxygen levels continued to fluctuate long after the Great Oxygenation Event 2.7 billion years ago, and that the oceans were many different flavors of anoxic right up until the Edicaran period, 600 million years ago. What happened in the intervening 2 billion years will be contested until scientists have more data, says a geochemist.