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Project Progress

This document reports on activities during year 1.5 through 2.5 of my NAI/NPP postdoctoral fellowship. I undertook significant model development and published an article on the astronomical detection of biogenic sulfur gases in Astrobiology (Domagal-Goldman et al., 2011). The above project addressed the “biosignatures” part of my NPP proposal, so I turned to the “biospheres” component and continued to build a case that biogenic sulfur metabolism played a vital role during the great oxidation event. We are actively exploring how biogenic sulfur gases may have affected the climate and chemistry of the late Archean and early Proterozoic (Claire and Kasting, 2010)

I enhanced the sulfur isotope photochemical model developed during the last period of performance to include higher order hydrocarbon species (e.g. Domagal-Goldman, 2008) and the newly discovered fractal scattering properties of organic haze particles (Wolf and Toon, 2010). We are investigating claims of self-shielding by SO₂ (Lyons, 2009), shielding by (potentially biogenic) OCS (Ueno et al. 2009), and CO₂ (Halevy et al. 2010). At AGU, I argued that these other works use oversimplified versions of atmospheric chemistry that are not sufficient to resolve the complexities of the Archean rock record (Claire and Kasting, 2010) and am nearing completion on a manuscript which suggests a novel interpretation of Earth’s sulfur isotope record.

Substantial effort has been directed toward understanding the linkages between the carbon and sulfur cycles on the Archean Earth. Working with international collaborators and exciting new data from an ancient carbonate platform, team members Claire and Domagal- Goldman have postulated a linkage between periods of enhanced methane production and changes in the atmospheric sulfur cycle observable in the geologic record. This work provides crucial evidence that the Earth may have been enshrouded in a Titan-like organic haze at certain time periods in the Archean. Furthermore, our recent work supports the argument that a thick haze is infeasible and that the Earth system may oscillate between two bi-stable states: thin-haze and clear skies (Zerkle et al, 2011)

Finally, during this period of performance, I completed my numerical model for the early Solar flux and its associated uncertainties (submitted for publication). Working with VPLinvestigators Martin Cohen, David Catling, John Sheets, and Vikki Meadows, I extended the results of Ribas et al. 2005 into the near UV, and have made quantitative predictions of the solar flux applicable to any place and time in the solar system.