Dating the rise of atmospheric oxygen

• Published in: Nature Vol. 427; no. 6970; pp. 117 - 120
• Main Authors: Bekker, A, Holland, H. D, Wang, P.-L, Rumble, D, Stein, H. J, Hannah, J. L, Coetzee, L. L, Beukes, N. J
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 08.01.2004; Nature Publishing Group
• Subjects: Atmosphere; Atmosphere - chemistry; Carbonates - analysis; Cold Climate; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fractionation; Geography; Geologic Sediments - chemistry; Geologic Sediments - microbiology; Geology; Ice; Iron - analysis; Isotope geochemistry; Isotope geochemistry. Geochronology; Isotopes; Oxygen; Oxygen - analysis; Petrology of sedimentary rocks except quaternary rocks; Pyrite; Sedimentary rocks; Sediments; South Africa; Sulfides - analysis; Sulfur - analysis; Time Factors; Transvaal South Africa; South Africa; Southern Africa; South Africa, Timeball Hill Formation; South Africa, Rooihoogte Formation; siderite; oxides; pyrite; Precambrian; stratigraphy; enrichment; pisolites; S-34/S-32; paleoatmosphere; Proterozoic; dating; oxygen; clastic rocks; sulfides; shale; stable isotopes; lower Proterozoic; pebbles; iron sulfides; iron oxides; Africa; microscope methods; hematite; carbonates; chemically precipitated rocks; iron formations; sedimentary rocks; glaciation; ironstone; oolite; isotope fractionation; organic materials
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature02260

Several lines of geological and geochemical evidence indicate that the level of atmospheric oxygen was extremely low before 2.45 billion years (Gyr) ago, and that it had reached considerable levels by 2.22 Gyr ago. Here we present evidence that the rise of atmospheric oxygen had occurred by 2.32 Gyr ago. We found that syngenetic pyrite is present in organic-rich shales of the 2.32-Gyr-old Rooihoogte and Timeball Hill formations, South Africa. The range of the isotopic composition of sulphur in this pyrite is large and shows no evidence of mass-independent fractionation, indicating that atmospheric oxygen was present at significant levels (that is, greater than 10(-5) times that of the present atmospheric level) during the deposition of these units. The presence of rounded pebbles of sideritic iron formation at the base of the Rooihoogte Formation and an extensive and thick ironstone layer consisting of haematitic pisolites and oölites in the upper Timeball Hill Formation indicate that atmospheric oxygen rose significantly, perhaps for the first time, during the deposition of the Rooihoogte and Timeball Hill formations. These units were deposited between what are probably the second and third of the three Palaeoproterozoic glacial events.