Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 114, Issue 13, Pages E2571-E2579Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1618798114
Keywords
sulfur mass-independent fractionation; organic haze; planetary oxidation; hydrogen loss; Neoarchean
Categories
Funding
- Natural Environment Research Council (NERC) Fellowship [NE/H016805]
- NERC Standard Grant [NE/J023485]
- SAGES Postdoctoral & Early Career Researcher Exchange grant
- Geological Society of London's Alan and Charlotte Welch Fund
- National Aeronautics and Space Administration
- NASA Exobiology program [NNX12AD91G]
- Royal Society Wolfson Research Merit Award
- European Research Council (ERC) under the European Union [678812]
- European Research Council (ERC) [678812] Funding Source: European Research Council (ERC)
- NASA [NNX12AD91G, 53372] Funding Source: Federal RePORTER
- Natural Environment Research Council [NE/J023485/1, NE/J022802/2, NE/J023485/2, NE/H016805/2, NE/H016805/1] Funding Source: researchfish
- NERC [NE/J023485/2, NE/H016805/2, NE/J023485/1, NE/H016805/1, NE/J022802/2] Funding Source: UKRI
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Emerging evidence suggests that atmospheric oxygen may have varied before rising irreversibly similar to 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 Delta S-36/Delta S-33 ratios are sensitive to the presence of haze. Exploiting existing age constraints, we estimate that organic haze developed rapidly, stabilizing within similar to 0.3 +/- 0.1 million years (Myr), and persisted for upward of similar to 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 delta C-13(Org) 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 x 10(18) moles of O-2 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.
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