Can organic haze and O₂ plumes explain patterns of sulfur mass-independent fractionation during the Archean?

The existence of mass-independently fractionated sulfur in Archean rocks is almost universally accepted as evidence for low atmospheric O₂ and O₃ concentrations at that time. But the detailed patterns of the Δ³³S values and of the ratios Δ³³S/δ³⁴S and Δ³⁶S/Δ³³S remain to be explained, and the mechanism for producing the mass-independent fractionation remains controversial. Here, we explore the hypothesis that the relatively low Δ³³S values seen during the Mid-Archean, 2.7-3.5 Ga, were caused by the presence of organic haze produced from photolysis of methane. This haze helped shield SO₂ from photolysis, while at the same time providing surfaces on which unfractionated short-chain sulfur species could condense. The evolution of oxygenic photosynthesis, and the concomitant disappearance of organic haze towards the end of the Archean allowed more negatively fractionated S₄ and S₈ to form, thereby generating large positive fractionations in other sulfur species, including sulfate and H₂S. Reduction of this sulfate to H₂S by bacteria, followed by incorporation of H₂S into pyrite, produced the large positive Δ³³S values observed in the Neoarchean rock record, 2.5-2.7 Ga.