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Early oxygenation of the terrestrial environment during the Mesoproterozoic


Geochemical data from ancient sedimentary successions provide evidence for the progressive evolution of Earth’s atmosphere and oceans1,2,3,4,5,6,7. Key stages in increasing oxygenation are postulated for the Palaeoproterozoic era (2.3 billion years ago, Gyr ago) and the late Proterozoic eon (about 0.8 Gyr ago), with the latter implicated in the subsequent metazoan evolutionary expansion8. In support of this rise in oxygen concentrations, a large database1,2,3,9 shows a marked change in the bacterially mediated fractionation of seawater sulphate to sulphide of Δ34S < 25‰ before 1 Gyr to ≥50‰ after 0.64 Gyr. This change in Δ34S has been interpreted to represent the evolution from single-step bacterial sulphate reduction to a combination of bacterial sulphate reduction and sulphide oxidation, largely bacterially mediated3,7,9. This evolution is seen as marking the rise in atmospheric oxygen concentrations and the evolution of non-photosynthetic sulphide-oxidizing bacteria3,7,10. Here we report Δ34S values exceeding 50‰ from a terrestrial Mesoproterozoic (1.18 Gyr old) succession in Scotland, a time period that is at present poorly characterized. This level of fractionation implies disproportionation in the sulphur cycle, probably involving sulphide-oxidizing bacteria, that is not evident from Δ34S data in the marine record1,2,3,9. Disproportionation in both red beds and lacustrine black shales at our study site suggests that the Mesoproterozoic terrestrial environment was sufficiently oxygenated to support a biota that was adapted to an oxygen-rich atmosphere, but had also penetrated into subsurface sediment.

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Figure 1: Compilation of published and new sulphur isotope compositions for sedimentary pyrite.
Figure 2: Map of NW Scotland showing outcrop of Stoer Group and sample localities.
Figure 3: Summary stratigraphic section of Stoer and Torridon groups.
Figure 4: Photomicrographs of Stoer Group sulphide/sulphate occurrences in shale host.


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We thank D. Fike for criticism of the manuscript; J. Still, J. B. Fulton and C. W. Taylor for technical help. S.S. is funded by the University of Aberdeen. NERC provides funding for the Argon Isotope and Isotope Community Support Facilities, and SUERC is financially supported by the Scottish Universities Consortium.

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Authors and Affiliations



J.P. directed the research; A.J.B. performed sulphur isotope analysis; D.M. performed Ar/Ar dating; J.P, S.B. and S.S. undertook field sampling; S.S. and S.B. performed petrographic analysis; J.P, A.B. and D.M. wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to John Parnell.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Stoer Group summary and references, Stac Fada Member summary, Ar/Ar methods, Ar/Ar brief discussion and references, Raw Ar/Ar data and step-heating spectrum with inverse and normal isochron plots, Raw sulphur isotope data, diagenetic sulphides and Raw sulphur isotope data, cross-cutting sulphides. (PDF 1003 kb)

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Parnell, J., Boyce, A., Mark, D. et al. Early oxygenation of the terrestrial environment during the Mesoproterozoic. Nature 468, 290–293 (2010).

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