The key objective of this proposal is to determine whether photolysis of SO2 gas is responsible for the unusual sulfur isotope signatures (called sulfur mass-independent fractionation, or S-MIF) seen in Archean sedimentary rocks. If so, then the present paradigm of using S-MIF as a proxy for the rise of atmospheric oxygen 2.4 Gyr ago is valid. We propose to measure the absorption cross sections of the 4 sulfur isotopologues of SO2 using the VUV Fourier transform spectrometer (FTS) at the SOLEIL synchrotron. We previously had made SO2 cross section measurements at Imperial College (IC), but found the quality of the light source was inadequate for the high-resolution work required for SO2. Our IC results on the 32, 33 and 34 isotopologues are consistent with the isotope signatures in the Archean rock record, but we were unable to complete the 36 measurements. At SOLEIL we will corroborate and refine the IC results, and re-measure the 36SO2 cross sections. Photochemical models are then used to compute the isotopic signatures implied by the SO2 cross sections for the early Earth atmosphere. This research will help to understand one of the most central events in Earth's early history, namely the rise of O2. The work falls under the Early Evolution of Life and the Biosphere component of the Exobiology program, and is central to understanding the evolution of O2-breathing life on terrestrial planets, a core objective in NASA Astrobiology.
|Effective start/end date||9/4/13 → 9/2/16|
- NASA: Goddard Space Flight Center: $227,751.00