Shale Cores (IMAGE) University of Washington Caption These are drill-cores of rocks from the Mount McRae Shale in Western Australia. Previous analysis showed a “whiff” of atmospheric oxygen preceding the Great Oxidation Event, 2.4 billion years ago. New analyses show a slightly earlier spike in minerals produced by volcanoes, which may have fertilized early communities of microbes to produce the oxygen. Credit Roger Buick/University of Washington Usage Restrictions With credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.