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Project Progress

Active trace gases that were produced by early biota had dramatic effects on the composition of the Earth’s atmosphere. Methane and more complex organic species, typically oxyenated or halogenated, interreacted to produce a temperature and ultraviolet (UV) shielding of the atmosphere that allowed life increasingly to dominate the Earth system.

Publications and discussion in the journal Nature by Catling, Zahnle, and McKay highlighted a fundamental change in the Earth’s redox state accomplished by compounds that carry hydrogen into the atmosphere. Catling emphasized the traditional H-carrier, methane. Chatfield’s and Singh’s work emphasize the importance of slightly more oxidized organic species, mainly acetone, acetaldehyde, and methyl halides. All these species both carry both H atoms and help determine the photochemical conditions of its escape to space.

A key longer-term effort is to simulate the Earth’s pre-O₂ and rise-of-O₂ period with a single simulation. In particular, modern understandings of appropriate ancient biogenic oceanic and terrestrial emissions need to be incorporated. An ongoing effort is to build an atmospheric one-dimensional model that can incorporate important detailed chemistry (nighttime and dawn-dusk reactions) in simulations relevant to geologic timescales. This is the ?minutes-to-millenia? model. A technique of periodic diel averaging successfully used in stratospheric simulations is employed. This model has been tested for current-Earth simulations of the very clean, ocean-dominated atmosphere, looking for insight on oceanic or other pervasive non-industrial emissions. First tests of the model for early, low-O₂ atmospheres and long time periods are in progress.