The Archean atmosphere was likely a weakly reduced mixture composed predominantly of N2 and CO2, with smaller concentrations of H2, CO, and CH4. Both CO2 and N2 may have been present in abundances exceeding today's values, by a factor of 2 or more for N2 and by factors of 100 or more for CO2. Published upper limits on CO2 from paleosols and banded iron formations are probably invalid; hence, CO2 could have been the dominant greenhouse gas that compensated for the fainter young Sun. The Archean greenhouse effect was likely supplemented by CH4, which could have risen to levels of 1000ppmv or more once methanogens had evolved. Warming by CH4 was limited to approximately 10-12°, however, by formation of organic haze. The key to analyzing Archean atmospheric composition is to understand the hydrogen budget of the atmosphere in which outgassing of H2 and other reduced gases from volcanoes was balanced by loss of hydrogen to space and burial of organic carbon in sediments. The mixing ratio of O2 in such a weakly reduced atmosphere would have been extremely low, roughly 10-13 at the surface, increasing to ~10-3 in the upper stratosphere. A rise in O2 just after the end of the Archean may have eliminated the methane greenhouse and triggered the Paleoproterozoic glaciations.
|Original language||English (US)|
|Title of host publication||The Atmosphere - History|
|Number of pages||19|
|State||Published - Nov 2013|
All Science Journal Classification (ASJC) codes
- Earth and Planetary Sciences(all)
- Environmental Science(all)