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Project Progress

Accomplishments:
1) My graduate student Alex Pavlov has been working with the CH4 photochemical model (originally developed by Lisa Brown) on a related project. We are trying to determine whether a hydrocarbon aerosol screen could have allowed photosynthetically-produced O2 to accumulate to significant levels during the Late Archean. Alex has performed all the necessary Mie scattering calculations and is in the process of incorporating them into the climate and photochemical models.
2) My grad student Trent Schindler has completed a paper on synthetic spectra of Earth-like planetary atmospheres. This is only tangentially related to the goals of our proposal, but it does tie in nicely with the photochemical modeling that Alex has been doing.
Comparison with stated goals in Task 1:
Originally, Martin Schoonen and I proposed to study the fate of CO produced by impacts and volcanism on the prebiotic Earth. Our thought was that CO would be the dominant carbon-bearing gas produced by large impacts and that CO could also be the dominant carbon-bearing gas emitted by surface volcanoes, if the upper mantle was originally more reduced.
Recently, at the Apr. 3-5 Astrobiology Meeting, Monika Kress and Chris McKay presented a poster paper in which they argued that CH4 and CO2, rather than CO, would have been the dominant carbon-bearing gases produced by impacts. Their idea is that vaporized metals from the impactor would have catalyzed the conversion of CO into CH4 as the impact plume cooled. If they are right, then it may behoove us to spend more time concentrating on CH4 photochemistry and less on CO. This is not necessarily bad from the standpoint of prebiotic synthesis. CH4 is a critical starting ingredient for hypotheses in which life originates in surface environments (as opposed to synthesis at deep-sea vents, which was the idea espoused in our original proposal).