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

In the citing paper

“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).”

In the citing paper

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

In the citing paper

“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).”

In the citing paper

“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).”

In the citing paper

“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).”

In the citing paper

“Second, Archean S-MIF requires >20-ppmv CH4 to generate particulate sulfur, S8 (Table 1).”

In the citing paper

“Evidence points to high levels of Archean CH4 (Fig. 3B).”

In the citing paper

“However, the production and preservation of non-mass-dependent sulfur isotope anomalies (NMD-S) in Archean and earliest Paleoproterozoic sedimentary rocks indicate that atmospheric pO 2 was maintained at extremely low values, likely below ∼10 -7 PAL, for most of Archean time (Farquhar et al. 2000, Pavlov & Kasting 2002, Zahnle et al. 2006) (Figure 3a).”

In the citing paper

“Photochemical models indicate that pO 2 must be above ∼10 -5 PAL to prevent the production and delivery of NMD-S anomalies near Earth's surface (Pavlov & Kasting 2002, Zahnle et al. 2006).”

In the citing paper

“Such a relationship is consistent with biogeochemical modeling that suggests the collapse of a methane greenhouse (immediately followed by ice ages) before the rise of atmospheric O2 (32).”

In the citing paper

“a decreased flux of methane led to greater oxygen concentrations in the atmosphere even if the marine O2 flux to the atmosphere remained constant”

In the citing paper

“Extremely low Proterozoic oxygen, however, is difficult to reconcile with photochemical models that show that O2 levels between 10−6 PAL and 0.1% PAL are unstable against small perturbations in the O2 source flux (39), favoring Po2 closer to the upper boundary used for our maximum disequilibrium calculations.”

In the citing paper

“favoring Po2 closer to the upper boundary used for our maximum disequilibrium calculations.”