Biological regulation of atmospheric chemistry en route to planetary oxygenation
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Emerging evidence suggests that atmospheric oxygen may have varied before rising irreversibly ∼2.4 billion years ago, during the Great Oxidation Event (GOE). Significantly, however, pre-GOE atmospheric aberrations toward more reducing conditions—featuring a methane-derived organic-haze—have recently been suggested, yet their occurrence, causes, and significance remain underexplored. To examine the role of haze formation in Earth’s history, we targeted an episode of inferred haze development. Our redox-controlled (Fe-speciation) carbon- and sulfur-isotope record reveals sustained systematic stratigraphic covariance, precluding nonatmospheric explanations. Photochemical models corroborate this inference, showing Δ36S/Δ33S ratios are sensitive to the presence of haze. Exploiting existing age constraints, we estimate that organic haze developed rapidly, stabilizing within ∼0.3 ± 0.1 million years (Myr), and persisted for upward of ∼1.4 ± 0.4 Myr. Given these temporal constraints, and the elevated atmospheric CO2 concentrations in the Archean, the sustained methane fluxes necessary for haze formation can only be reconciled with a biological source. Correlative δ13COrg and total organic carbon measurements support the interpretation that atmospheric haze was a transient response of the biosphere to increased nutrient availability, with methane fluxes controlled by the relative availability of organic carbon and sulfate. Elevated atmospheric methane concentrations during haze episodes would have expedited planetary hydrogen loss, with a single episode of haze development providing up to 2.6–18 × 1018 moles of O2 equivalents to the Earth system. Our findings suggest the Neoarchean likely represented a unique state of the Earth system where haze development played a pivotal role in planetary oxidation, hastening the contingent biological innovations that followed.
Izon , G , Zerkle , A L , Williford , K , Farquhar , J , Poulton , S & Claire , M W 2017 , ' Biological regulation of atmospheric chemistry en route to planetary oxygenation ' Proceedings of the National Academy of Sciences of the United States of America , vol 114 , no. 13 , pp. 2571-2579 . DOI: 10.1073/pnas.1618798114
Proceedings of the National Academy of Sciences of the United States of America
© 2017, the Authors. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at: https://doi.org/10.1073/pnas.1618798114
This study was supported financially by a Natural Environment Research Council Fellowship NE/H016805 (to A.Z.) and a Natural Environment Research Council Standard Grant NE/J023485 (to A.Z., M.C. and S.P.). Further financial support was generously provided via a SAGES Postdoctoral & Early Career Researcher Exchange grant and The Geological Society of London’s Alan and Charlotte Welch Fund (to G.I.). For his work performed at the Jet Propulsion Laboratory, California Institute of Technology, KHW acknowledges the support of a grant from the National Aeronautics and Space Administration. JF acknowledges funding from the NASA Exobiology program (NNX12AD91G).
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