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The production of trace gases by photochemistry and lightning in the early atmosphereRecent atmospheric calculation suggest that the prebiological atmosphere was most probably composed of nitrogen, carbon dioxide, and water vapor, resulting from volatile outgassing, as opposed to the older view of a strongly reducing early atmosphere composed of methane, ammonia, and hydrogen. Photochemical calculations indicate that methane would have been readily destroyed via reaction with the hydroxyl radical produced from water vapor and that ammonia would have been readily lost via photolysis and rainout. The rapid loss of methane and ammonia, coupled with the absence of a significant source of these gases, suggest that atmospheric methane and ammonia were very short lived, if they were present at all. An early atmosphere of N2, CO2, and H2O is stable and leads to the chemical production of a number of atmospheric species of biological significance, including oxygen, ozone, carbon monoxide, formaldehyde, and hydrogen cyanide. Using a photochemical model of the early atmosphere, the chemical productionof these species over a wide range of atmospheric parameters were investigated. These calculations indicate that early atmospheric levels of O3 were significantly below the levels needed to provide UV shielding. The fate of volcanically emitted sulfur species, e.g., sulfur dioxide and hydrogen sulfide, was investigated in the early atmosphere to assess their UV shielding properties. The photochemical calculations show that these species were of insufficient levels, due in part to their short photochemical lifetimes, to provide UV shielding.
Document ID
19860017379
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Levine, J. S.
(NASA Langley Research Center Hampton, VA, United States)
Tennille, G. M.
(NASA Langley Research Center Hampton, VA, United States)
Towe, K. M.
(Smithsonian Institution Washington, D. C., United States)
Khanna, R. K.
(Maryland Univ. College Park., United States)
Date Acquired
August 12, 2013
Publication Date
May 1, 1986
Publication Information
Publication: NASA, Washington Second Symposium on Chemical Evolution and the Origin and Evolution of Life
Subject Category
Geophysics
Accession Number
86N26851
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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