It is widely assumed that atmospheric oxygen concentrations remained persistently low (less than 10−5 times present levels) for about the first 2 billion years of Earth’s history1. The first long-term oxygenation of the atmosphere is thought to have taken place around 2.3 billion years ago, during the Great Oxidation Event2,3. Geochemical indications of transient atmospheric oxygenation, however, date back to 2.6–2.7 billion years ago4,5,6. Here we examine the distribution of chromium isotopes and redox-sensitive metals in the approximately 3-billion-year-old Nsuze palaeosol and in the near-contemporaneous Ijzermyn iron formation from the Pongola Supergroup, South Africa. We find extensive mobilization of redox-sensitive elements through oxidative weathering. Furthermore, using our data we compute a best minimum estimate for atmospheric oxygen concentrations at that time of 3 × 10−4 times present levels. Overall, our findings suggest that there were appreciable levels of atmospheric oxygen about 3 billion years ago, more than 600 million years before the Great Oxidation Event and some 300–400 million years earlier than previous indications for Earth surface oxygenation.
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N. Planavsky, R. Schoenberg, S. Poulton, A. Basu, C. Jones, H. Tsikos, A. Mucci, A. O’Neill and T. Dahl are thanked for suggestions. T. Larsen, C. N. Jensen, T. Leeper and P. Søholt are acknowledged for technical support. Funding to S.A.C. was provided by an Agouron Institute Geobiology Fellowship and an NSERC PDF. Additional funding was from the Danish National Research Foundation (grant no. DNRF53), the Danish Agency for Science, Technology, and Innovation, the European Research Council and the National Research Foundation in Pretoria. The palaeosol drill core was made available by Ian Frith of AngloGold Ashanti Exploration (SA), from their core store in Carltonville, South Africa.
The authors declare no competing financial interests.
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Crowe, S., Døssing, L., Beukes, N. et al. Atmospheric oxygenation three billion years ago. Nature 501, 535–538 (2013). https://doi.org/10.1038/nature12426
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