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Oxygen dynamics in the aftermath of the Great Oxidation of Earth's atmosphere - PubMed

  • ️Tue Jan 01 2013

Oxygen dynamics in the aftermath of the Great Oxidation of Earth's atmosphere

Donald E Canfield et al. Proc Natl Acad Sci U S A. 2013.

Abstract

The oxygen content of Earth's atmosphere has varied greatly through time, progressing from exceptionally low levels before about 2.3 billion years ago, to much higher levels afterward. In the absence of better information, we usually view the progress in Earth's oxygenation as a series of steps followed by periods of relative stasis. In contrast to this view, and as reported here, a dynamic evolution of Earth's oxygenation is recorded in ancient sediments from the Republic of Gabon from between about 2,150 and 2,080 million years ago. The oldest sediments in this sequence were deposited in well-oxygenated deep waters whereas the youngest were deposited in euxinic waters, which were globally extensive. These fluctuations in oxygenation were likely driven by the comings and goings of the Lomagundi carbon isotope excursion, the longest-lived positive δ(13)C excursion in Earth history, generating a huge oxygen source to the atmosphere. As the Lomagundi event waned, the oxygen source became a net oxygen sink as Lomagundi organic matter became oxidized, driving oxygen to low levels; this state may have persisted for 200 million years.

Keywords: GOE; Mo isotope; Paleoproterozoic; marine chemistry; trace metal.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.

Distribution of the elements and isotopes in Francevillian sediments used to reconstruct depositional environment (see also

Fig. S1

for additional data), as also indicated on the figure. There may be a thin ferruginous interval near the top of the FB1b subunit as indicated. A reconstruction of relative sea-level trends is also shown as well as available chronological constraints.

Fig. 2.
Fig. 2.

Further trace metal and isotope data through the Francevillian sediments. Plotted also are metal enrichment factors (EF) for Mo and U. EF = (Xsediment/AlSediment)/(XCrust/AlCrust). X, metal content (wt%).

Fig. 3.
Fig. 3.

(Upper) Reconstruction of relative trends in levels of oxygen based on information given in the text. Dotted line represents a time with little constraint as discussed in the text. (Lower) Outlines the timing of the depositional units used to reconstruct oxygen trends. Also shown are the depositional environment for the Francevillian sediments as shown in Fig. 1 as well as indications of intervals of massive bedded gypsum deposition as presented in refs. and . The timing of the Huronian glaciations are after ref. , and the GOE after ref. . Uncertainties in the dating of the different deposits are represented in the length of the horizontal bars representing the various fields (see Results and Discussion, Ocean and Atmospheric Oxygenation in the Wake of Lomagundi Excursion for details). The chronology of the Francevillian sediments is discussed in the text. Note that the shungite deposits of Fennoscandia have been previously linked with deposition of the FD unit from Gabon (33).

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