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Project Progress

The second complete year of this module work has accomplished the technical objective: production of a respectable modern atmospheric chemistry model, which has been incarnated as GAIA, Global Atmospheric Integrator for Astrobiology. GAIA is capable of extending full diel variability of emissions and photochemical concentrations to estimate the composition of a planetary atmosphere on a geologic timescale. GAIA incorporates fully modern descriptions of atmospheric photolysis and ultraviolet (UV) shielding, photochemical reactions, thermal reactions, a simple water cycle, and lower and upper driving fluxes, i.e., biogeochemical interchange and hydrogen escape. It is driven by data tables where possible, making it easy to accomplish parameter studies and to share with other research groups. GAIA performs stably as fluxes of O₂ and reduced (CH₄, H₂) gases are increased, thus allowing a full study of composition accompanying the rise of aerobic life. Interactions with the radiative consequences of composition must be iterated offline, at this point. Previously, there was a “forbidden zone” of parameters using prior models where convergence was not possible, and separate “low-productivity” and “nearly modern” regimes were required. The difficulties of the “forbidden zone” are of course promising that there might be purely chemical instabilities in Earth’s oxic transition. We have found none, yet. Simulations of atmospheric concentrations of greenhouse gases can be achieved for a larger spectrum of plausible O₂ and reduced-gas emissions fluxes. The significance of this technology is that we may simulate conditions for the full rise of O₂ in the Earth’s atmosphere, including periods associated with “Snowball Earth” and other interesting episodes. The model has been adopted by University of Washington for use by Dr. David Catling’s group. Mr. Mark Claire, a member of Dr. Catling’s group, has received a Graduate Student Research Program grant that will enable him to apply the simulation technique.