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RESEARCH PROJECTS: Geochemical Records of the Earth's Biosphere Photochemical Reactions of Sulfur and Iron in the Early Earth The Genomic Record of Earth's Early Biosphere Laboratory Microbial Simulations: Astrobiological Signatures |
SECTION II: Photochemical Reactions of Sulfur and Iron in the Early Earth
To understand the mechanism(s) for the creation of mass independent fractionation of S isotopes and to aid in the reconstruction of the Precambrian S cycle using the S isotope record in rocks, we will conduct a series of photochemical reactions of SO2 by utilizing an innovative experimental technique developed by Castleman: a reflectron time-of-flight mass spectrometer (RETOF-MS) and a femtosecond laser system coupled with the pump-probe technique. We will also conduct photochemical experiments on Fe-bearing compounds to aid in understanding the formational mechanisms of banded iron-formations and seawater sulfate. Modeling of atmospheric reactions and isotopic analyses of the experimental products will help focus interpretations of the S isotope record in rocks. The following figure (from Farquhar et al., Science 289, 756, 2000) shows deviations in delta 33-S from the normal mass-dependent fractionation line prior to ~2.2 billion years ago. One of PSARC's goals is to understand the photochemical processes that may create such "mass-independent" fractionation of sulfur isotopes. A combination of laboratory work and theoretical modeling is planned to address this question.
What mechanisms create mass independent fractionation of sulfur isotopes? |
