ATMOSPHERIC SCIENCE: Air Supplies

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Science  16 Nov 2001:
Vol. 294, Issue 5546, pp. 1419a
DOI: 10.1126/science.294.5546.1419a

Although uncertainty remains, the Archean atmosphere up to about 3 billion years ago is thought to have been rich in CO2 and H2O. An oxygen-rich atmosphere may have evolved in stages starting about 2 to 2.4 billion years ago, perhaps driven in part by the evolution or increased abundance of photosynthetic bacteria, which released oxygen.

Kasting et al. now suggest that the rise of methanogenic bacteria also left their mark on Earth's atmosphere. An enigmatic drop in the carbon isotope record of the early Earth may reflect abundant methane in Earth's atmosphere released by these bacteria. Coupled with the rise of oxygenic photosynthesis about 3 to 2.5 billion years ago, this event helped to pave the way to an oxygen-rich atmosphere.—BH

Geology 29, 1003 (2001).

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