Atmospheric Influence of Earth's Earliest Sulfur Cycle

In the citing paper

“Δ³³S isotopic values can be used to determine whether sulfate aerosol formation occurred in the stratosphere (i.e., above the ozone layer) since UV photochemical reactions generate MIF and non-zero Δ³³S 40,122-124 .”

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

“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

“whereas geologic and geochemical constraints suggest that before ~2.45 billion years ago (Ga), the atmosphere was essentially devoid of this gas (1–4).”

In the citing paper

“Mass-independent fractionation of sulfur isotopes (S-MIF) is thought to originate from the photolysis and/or photoexcitation of volcanogenic SO2 by ultraviolet light in an anoxic atmosphere (1, 20–23).”

In the citing paper

“By accepting the original value of ~10−5 PAL as the nominal threshold above which S-MIF is no longer preserved, we apply it here as a robust tool for tracing the first rise in pO2 to >10−5 PAL because of its potential for high stratigraphic resolution (1, 31, 33).”

In the citing paper

“For simplicity, we did not explicitly model different kinetics for different forms of sulfur (for example, thiosulfate, S8, or sulfate) that are likely present in the Archean oceans (1, 30).”

In the citing paper

“Atmospheric oxygen (pO2) rose from <10−5 present atmospheric level (PAL) at the Great Oxidation Event, as constrained by the disappearance of mass-independent fractionation of sulfur isotopes1 (MIF-S) ∼2.45–2.32 Ga.”

In the citing paper

“However, the lack of MIF-S1 after 2.32 Ga constrains pO2>10−5 PAL.”

In the citing paper

“In the rock record, this event is manifested by a number of changes (see Farquhar et al., 2011, 2014, for reviews), including (1) loss of easily oxidisable detrital uraninite, pyrite, and siderite from fluvial siliciclastic sediments at ca. 2.4 Ga”

In the citing paper

“that effectively disappeared from the sedimentary record between 2.45 and 2.32 Ga (e.g., Bekker et al., 2004;Farquhar et al., 2000;2011).”

In the citing paper

“The disappearance of S-MIF is perhaps the most accepted evidence for the onset of widespread and permanent oxygenation of the Earth's surface to levels above 10 -5 times present atmospheric levels (PAL) (see Pavlov and Kasting, 2002;Bekker et al., 2004;Farquhar et al., 2000;2011).”

In the citing paper

“There was virtually no oxygen in the Archean eon [4.0 to 2.5 billion years ago (Ga)] (12)”