2002 Annual Science Report
NASA Ames Research Center Reporting | JUL 2001 – JUN 2002
Biogeochemistry of Earth's Greenhouse Leading to the Rise of Oxygen
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.
PROJECT MEMBERS:Robert Chatfield
RELATED OBJECTIVES:Objective 1.0
Determine whether the atmosphere of the early Earth, hydrothermal systems or exogenous matter were significant sources of organic matter.
Describe the sequences of causes and effects associated with the development of Earth's early biosphere and the global environment.
Define climatological and geological effects upon the limits of habitable zones around the Sun and other stars to help define the frequency of habitable planets in the universe.
Define an array of astronomically detectable spectroscopic features that indicate habitable conditions and/or the presence of life on an extrasolar planet.
Determine the resilience of local and global ecosystems through their response to natural and human-induced disturbances.
Model the future habitability of Earth by examining the interactions between the biosphere and the chemistry and radiation balance of the atmosphere.