8
January 2004
Atmospherics: The oxygen horizon
The atmosphere of the primitive Earth probably contained nitrogen, carbon dioxide and water vapour, among other gases, but virtually no free oxygen, which is essential for life as we know it. Free oxygen was eventually introduced into the atmosphere by photosynthetic microorganisms. Various lines of evidence suggest that atmospheric oxygen levels were extremely low before 2.45 billion years ago, but had increased by 2.22 billion years ago. Work continues on pinning down an exact date for this important event, and Bekker et al. present the most precise measurement yet. They push back the date for the first rise of atmospheric oxygen to 2.32 billion years ago. The evidence comes from sulphur isotope data in the organic-rich shales of the Rooihoogte and Timeball Hill formations in South Africa.
Dating the rise of atmospheric oxygen
A. BEKKER, H. D. HOLLAND, P.-L. WANG, D. RUMBLE III,
H. J. STEIN, J. L. HANNAH, L. L. COETZEE & N. J. BEUKES
Nature 427, 117–120 (2004); doi:10.1038/nature02260
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