Organosulfur Aerosols Likely Carried Sulfur MIF Signatures in the Early Earth’s Atmosphere

Signatures of mass‐independent fractionation (MIF) of sulfur in Archean sulfide and sulfate minerals are widely thought to record an anoxic early Earth’s atmosphere. While experiments of ultraviolet irradiation of SO2 produce significant sulfur mass‐independent fractionation (S‐MIF) in reaction products (elemental sulfur and residual sulfur dioxide), they have not been able to reproduce the isotope patterns, in particular Δ36S/Δ33S ratios, observed in the geologic rock record. Studies that focused on organic sulfur gases and hazes in Archean did not report organosulfur aerosol photoproducts as major contributors to Archean S‐MIF chemistry. Here we show, for the first time, that photochemical reactions of SO2 in the presence of gaseous hydrocarbons (CH4, C2H2, and C2H4) produce haze‐like organosulfur aerosols bearing S‐MIF with variable Δ36S/Δ33S ratios. The isotope trends for the organosulfur photoproducts produced in our experiments suggest that in addition to elemental sulfur, organosulfur compounds—in particular methanesulfonic acid—are a key component of S‐MIF signals from the atmosphere to the ocean and sediments with possible links to Archean atmosphere warmed by a methane greenhouse. Plain Language Summary Experimental ultraviolet irradiation of SO2 demonstrably induces an anomalous or mass‐independent fractionation of sulfur (S‐MIF) as evidence of an irreversible rise in atmospheric oxygen at ca. 2.4 Ga. Hitherto, such in vitro approaches did not completely confirm the variation in the S‐MIF archived in early Earth’s rock record. Here, we show that the photolysis of SO2 in the presence of reduced hydrocarbon gases produced haze‐like organosulfur aerosol photoproducts that are thought to be strongly modulated by early Earth’s atmospheric sulfur cycling and its role in S‐MIF transfer and preservation in Archean sedimentary rock record. Key Points The SO2‐CH4 photoproducts exhibit negative Δ36S/Δ33S slopes of −1.9 that is closer to the Archean reference fractionation window