Atmospheric Oxygen And Methane On The Early Earth
The habitability of the early Earth was affected by various factors. We focus here on atmospheric oxygen (O2) and methane (CH4). O2 is essential for supporting eukaryotic life, including plants and animals.
CH4, along with CO2 and H2O, is a powerful greenhouse gas that may have helped offset the lower luminosity of the young Sun. Its concentration is disputed, though, in both the Archean and Proterozoic eons.
The CH4 concentration depends strongly on atmospheric O2, which began to be produced biologically in geochemically significant amounts sometime during the Archean, probably near 2.7 Ga, based on the mass-independent sulphur isotope record and other (C and N) isotopic data. O2 was produced by cyanobacteria living in terrestrial mats and in the surface ocean during this time, generating localized oxygen oases that vented O2 into the atmosphere.
Sometime between 2.2 and 2.4 Ga, a Great Oxidation Event occurred, causing O2 to increase substantially, likely to approximately 10 per cent of present levels. Increases in O2 near the beginning and end of the Proterozoic may have caused methane to decrease, triggering the Snowball Earth glaciations observed during both time intervals.
- Atmospheric oxygen and methane on the early Earth, Philosophical Transactions b via PubMed (open access)
- Atmospheric oxygen and methane on the early Earth Open Access, Philosophical Transactions b (open access)
Astrobiology,
