Cited by 315Paleontology and Stratigraphy of FossilsEarth Systems and Cosmic EvolutionGeological and Geochemical Analysis

The loss of mass‐independent fractionation in sulfur due to a Palaeoproterozoic collapse of atmospheric methane

ZAHNLE, K., CLAIRE, M., CATLING, D.·2006·Geobiology

Abstract

We use a 1‐D numerical model to study the atmospheric photochemistry of oxygen, methane, and sulfur after the advent of oxygenic photosynthesis. We assume that mass‐independent fractionation (MIF) of sulfur isotopes – characteristic of the Archean – was best preserved in sediments when insoluble elemental sulfur (S 8) was an important product of atmospheric photochemistry. Efficient S 8 production requires three things: (i) very low levels of tropospheric O 2; (ii) a source of sulfur gases to the atmosphere at least as large as the volcanic SO 2 source today; and (iii) a sufficiently high abundance of methane or other reduced gas. All three requirements must be met. We suggest that the disappearance of a strong MIF sulfur signature at the beginning of the Proterozoic is better explained by the collapse of atmospheric methane, rather than by a failure of volcanism or the rise of oxygen. The photochemical models are consistent in demanding that methane decline before O 2 can rise (although they are silent as to how quickly), and the collapse of a methane greenhouse effect is consistent with the onset of major ice ages immediately following the disappearance of MIF sulfur. We attribute the decline of methane to the growth of the oceanic sulfate pool as indicated by the widening envelope of mass‐dependent sulfur fractionation through the Archean. We find that a given level of biological forcing can support either oxic or anoxic atmospheres, and that the transition between the anoxic state and the oxic state is inhibited by high levels of atmospheric methane. Transition from an oxygen‐poor to an oxygen‐rich atmosphere occurs most easily when methane levels are low, which suggests that the collapse of methane not only caused the end of MIF S and major ice ages, but it may also have enabled the rise of O 2. In this story the early Proterozoic ice ages were ended by the establishment of a stable oxic atmosphere, which protected a renewed methane greenhouse with an ozone shield.

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Crossref · 10.1111/j.1472-4669.2006.00085.x

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  • In anoxic air, sulfur ends up in insoluble S8 aerosols and water-soluble sulfate and SO2, unlike today's atmospheric sulfur, which almost entirely oxidizes to sulfate.

    “In anoxic air, sulfur ends up in insoluble S8 aerosols and water-soluble sulfate and SO2, unlike today’s atmospheric sulfur, which almost entirely oxidizes to sulfate (44, 45).”

    From The Archean atmosphere (2020) · cites this paper as [44]

  • For a wide range of Archean atmospheric redox conditions, both types of aerosol should form and precipitate.

    “For a wide range of Archean atmospheric redox conditions, both types of aerosol should form and precipitate (44).”

    From The Archean atmosphere (2020) · cites this paper as [44]

  • The strongest constraint on Archean atmospheric composition is that the ground-level mixing ratio of O2 was <10−6 PAL or <0.2 ppmv O2 for air of 1 bar, indicated by the presence of sulfur isotope MIF in Archean sedimentary minerals.

    “The strongest constraint on Archean atmospheric composition is that the ground-level mixing ratio of O2 was <10−6 PAL (present atmospheric level) or <0.2–parts per million by volume (ppmv) O2 for air of 1 bar, indicated by the presence of sulfur isotope MIF (S-MIF) in Archean sedimentary minerals (Fig. 2A) (44, 47).”

    From The Archean atmosphere (2020) · cites this paper as [44]

  • In the Archean, gases such as CH4 or H2 produced sufficiently reducing conditions that S, S2, S3, etc. gases persisted and polymerized into S8.

    “In the Archean, as well as anoxia, gases such as CH4 or H2 produced sufficiently reducing conditions that S, S2, S3, etc. gases persisted and polymerized into S8 (44, 60).”

    From The Archean atmosphere (2020) · cites this paper as [44]

  • Permanent atmospheric oxygenation requires ~3 × 10−3 PAL O2 or more to prevent a destabilizing positive feedback of photochemical destruction of tropospheric O2.

    “Permanent atmospheric oxygenation requires ~3 × 10−3 PAL O2 or more to prevent a destabilizing positive feedback of photochemical destruction of tropospheric O2 that otherwise occurs when an incipient ozone column is still transparent to far UV (44, 121, 122).”

    From The Archean atmosphere (2020) · cites this paper as [44]

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Authors
ZAHNLE, K., CLAIRE, M., & CATLING, D.
Affiliations
  • Ames Research Center (US)
  • University of Washington (US)
Corresponding author
ZAHNLE, K.
Venue
Geobiology
Publisher
Wiley
Published
2006-10-16
Volume
4
Issue
4
Pages
271-283
ISSN
  • 1472-4669 (ISSN-L)
  • 1472-4677
OpenAlex
W1999845220
Cited by
315
References
65
Citations by year
2026: 10 · 2025: 23 · 2024: 13 · 2023: 21 · 2022: 17 · 2021: 26 · 2020: 24 · 2019: 14 · 2018: 28 · 2017: 20 · 2016: 13 · 2015: 8 · 2014: 12 · 2013: 19 · 2012: 15
FWCI
8.90
Type
journal article
Language
en
Open access
closed
Locations
  • Geobiology (publishedVersion)
  • Explore Bristol Research (publishedVersion)
  • Bristol Research (University of Bristol) (submittedVersion)
Funders
National Aeronautics and Space Administration
Topics
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
  • Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Earth Systems and Cosmic Evolution
  • Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
Keywords
atmospheric photochemistry, oxygenic photosynthesis, sulfur cycling, elemental sulfur, atmospheric oxygen rise, Archean, volcanic SO2

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