Testing the Discovery of Archean Terrestrial Mass-independent Sulfur Isotope Anomalies

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

Abstract EAR-0125096 Rumble Carnegie Institution of Washington, Geophysical Laboratory The primary goal of this proposal is to confirm the discovery of mass-independent sulfur isotope fractionation by replicate analyses to validate accuracy and to identify mineral hosts of anomalous sulfur and measure its heterogeneity. The motivation for additional study of sulfur isotope analyses is because of their utility as biomarkers in ancient rocks. In Precambrian rocks where fossils are non-existent and organic residues have been converted to carbon, sulfur isotope mass-dependent fractionations remain as an indelible record of the vital processes of sulfate-reducing microbes. With the discovery of mass-independent sulfur isotope fractionations in Archean rocks, sulfur isotope geochemistry has acquired even greater significance. Such fractionations are known in the upper atmosphere where gas phase reactions take place under the strong influence of ultraviolet light. Sulfur isotope analyses, therefore, may give evidence for the former existence of life but they may also record a previously unknown chapter in the evolution of Earth's atmosphere. This proposal will examine the distribution of anomalous sulfur geographically in Archean and Proterozoic metamorphic rocks. Stratigraphic sections will be measured to establish a sulfur isotope fractionation time distribution. The new sulfur isotope laser fluorination microprobe at the Geophysical Laboratory of the Carnegie Institution will be used to do detailed examination of Archean and Proterozoic metamorphic rocks.