Speaker: Andrew Whitehill (MIT)
Abstract: Sulfur isotope mass-independent fractionation (S-MIF) is ubiquitous in Archean and Paleoproterozoic sedimentary rocks and provides the most convincing evidence for a low-oxygen early (pre-2.4 Ga) atmosphere. The abrupt disappearance of S-MIF, believed to be coincident with the rise of atmospheric oxygen, represents one of the most striking evolutionary changes in Earth's surface environment. S-MIF has the potential to provide constraints on environmental conditions during the Archean; however, interpretation of these signatures is limited by the lack of a mechanistic understanding of S-MIF production. I will present results from a series of experiments testing the effect of pressure, temperature, and other variables on the isotopic fractionation during photochemical reactions of sulfur dioxide. Results of photolysis experiments match signatures observed in modern stratospheric sulfate aerosols, but are inconsistent with the signatures in Archean rocks. I will discuss S-MIF production mechanisms, summarize and evaluate the current state of S-MIF research, and suggest future research directions.