Rocks reveal an oxygenated ocean earlier than assumed
By Julie Spitzer | Dec. 1, 2015The oceans of the Archean were nothing like today’s vast blue pools. In fact, these oceans lacked free oxygen. Until recently, it was thought the oceans’ water columns were uniformly anoxic until the Great Oxidation Event, which occurred 2.4-2.2 billion years ago. However, researchers at UW-Madison have discovered evidence of free oxygen in Earth’s shallow oceans much earlier.