T20 Changes in Ocean and Atmospheric Redox State and the Evolution of Life I
Sunday, 22 October 2006
8:00 AM - 12:00 PM
ABRUPT ONSET OF SUBAERIAL VOLCANISM AND THE RISE OF ATMOSPHERIC OXYGEN
Paper number: T20-1
Program: Technical Sessions
Time: 8:00 AM – 8:20 AM
Authors
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Mark E. BarleyThe Univ of Western Australia, Crawley, N/A
Abstract
The simple hypothesis that the establishment of an oxygen-rich atmosphere ~2.4 billion years ago occurred when oxygen-producing cyanobacteria evolved is arguably contradicted by abundant biomarker evidence for their presence in rocks 300-million years older. Given the event's coincidence with the transition from the Archean to the Proterozoic Eons, a cause-and-effect relationship with the defining tectonic change (the stabilization of continental cratons) seems likely. A shift in the locus of volcanism from largely submarine to a mix of submarine and subaerial is here argued to be the primary cause. This shift would have been accompanied by a significant reduction in the sink for oxygen provided by reduced volcanic gases: Archean submarine volcanoes emitted molecular hydrogen in excess, allowing H2 to accumulate in the atmosphere and prevent the buildup of oxygen, whereas Proterozoic subaerial/submarine volcanoes did not, so oxygen came to dominate atmospheric composition.