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Widespread iron-rich conditions in the mid-Proterozoic ocean


The chemical composition of the ocean changed markedly with the oxidation of the Earth’s surface1, and this process has profoundly influenced the evolutionary and ecological history of life2,3. The early Earth was characterized by a reducing ocean–atmosphere system, whereas the Phanerozoic eon (less than 542 million years ago) is known for a stable and oxygenated biosphere conducive to the radiation of animals. The redox characteristics of surface environments during Earth’s middle age (1.8–1 billion years ago) are less well known, but it is generally assumed that the mid-Proterozoic was home to a globally sulphidic (euxinic) deep ocean2,3. Here we present iron data from a suite of mid-Proterozoic marine mudstones. Contrary to the popular model, our results indicate that ferruginous (anoxic and Fe2+-rich) conditions were both spatially and temporally extensive across diverse palaeogeographic settings in the mid-Proterozoic ocean, inviting new models for the temporal distribution of iron formations and the availability of bioessential trace elements during a critical window for eukaryotic evolution.

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Figure 1: Iron speciation and sulphur isotope data for mid-Proterozoic shales.
Figure 2: Summary of marine chemical conditions in the Precambrian.

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We thank P. Emsbo, S. Bull and D. Winston for formative discussions, P. Fralick for constructive comments, and S. Bates and J. Owens for assistance with the analyses. This work was supported by funding from the National Science Foundation (NSF) Graduate Research Fellowship programme, Geological Society of America and American Philosophical Society, to N.J.P.; from the NSF Division of Earth Sciences, the NASA Exobiology Program and Astrobiology Institute and the UTAS Visiting Fellows programme to T.W.L.; from the Agouron Institute to T.W.L. and G.D.L; and from Natural Sciences and Engineering Research Council of Canada to A.B. P.McG. was supported through the Australian Research Council’s Centre of Excellence programme.

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P.McG., A.B., T.W.L., X.C., C.L. and N.J.P. collected samples, and P.McG., N.J.P., C.T.S. and C.L. analysed them. All authors were involved in the writing and the design and interpretations of this study.

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Correspondence to Timothy W. Lyons.

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Planavsky, N., McGoldrick, P., Scott, C. et al. Widespread iron-rich conditions in the mid-Proterozoic ocean. Nature 477, 448–451 (2011).

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