Molybdenum Isotope Evidence for Widespread Anoxia in Mid-Proterozoic Oceans

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Science  02 Apr 2004:
Vol. 304, Issue 5667, pp. 87-90
DOI: 10.1126/science.1091785

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How much dissolved oxygen was present in the mid-Proterozoic oceans between 1.8 and 1.0 billion years ago is debated vigorously. One model argues for oxygenation of the oceans soon after the initial rise of atmospheric oxygen ∼2.3 billion years ago. Recent evidence for H2S in some mid-Proterozoic marine basins suggests, however, that the deep ocean remained anoxic until much later. New molybdenum isotope data from modern and ancient sediments indicate expanded anoxia during the mid-Proterozoic compared to the present-day ocean. Consequently, oxygenation of the deep oceans may have lagged that of the atmosphere by over a billion years.

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