The Archean atmosphere
Abstract
What was the early atmosphere made of? We review what is known during the Archean eon, 4 to 2.5 billion years ago.The atmosphere of the Archean eon—one-third of Earth's history—is important for understanding the evolution of our planet and Earth-like exoplanets. New geological proxies combined with models constrain atmospheric composition. They imply surface O2levels <10−6times present, N2levels that were similar to today or possibly a few times lower, and CO2and CH4levels ranging ~10 to 2500 and 102to 104times modern amounts, respectively. The greenhouse gas concentrations were sufficient to offset a fainter Sun. Climate moderation by the carbon cycle suggests average surface temperatures between 0° and 40°C, consistent with occasional glaciations. Isotopic mass fractionation of atmospheric xenon through the Archean until atmospheric oxygenation is best explained by drag of xenon ions by hydrogen escaping rapidly into space. These data imply that substantial loss of hydrogen oxidized the Earth. Despite these advances, detailed understanding of the coevolving solid Earth, biosphere, and atmosphere remains elusive, however.
- Publication:
-
Science Advances
- Pub Date:
- February 2020
- DOI:
- 10.1126/sciadv.aax1420
- Bibcode:
- 2020SciA....6.1420C