Large-scale fluctuations in Precambrian atmospheric and oceanic oxygen levels from the record of U in shales
Abstract
The atmosphere–ocean system experienced a progressive change from anoxic to more oxidizing conditions through time. This oxidation is traditionally envisaged to have occurred as two stepwise increases in atmospheric oxygen at the beginning and end of the Proterozoic Eon. Here, we present a study of the redox-sensitive element, uranium, in organic-rich shales to track the history of Earth's surface oxidation at an unprecedented temporal resolution. Fluctuations in the degree of uranium enrichment in organic-rich shales suggest that the initial rise of atmospheric oxygen ~2.4 billion yr ago was followed by a decline to less oxidizing conditions during the mid-Proterozoic. This redox state persisted for almost 1 billion yr, ending with a second oxygenation event in the latest Neoproterozoic. The U record tracks major fluctuations in surface oxygen level and challenges conventional models that suggest the Earth underwent a unidirectional rise in atmospheric oxygen during the Precambrian.
Additional Information
© 2013 Elsevier B. V. Received 17July 2012; Received in revised form 17 March 2013; Accepted 23 March 2013; Editor: G. Henderson. Available online 25 April 2013. Funding was provided by the NSERC Discovery Grant to A.B.; NSF-EAR Program (Grant EAR-0720362 to T.W.L. and G.D.L.); the NASA Exobiology Program and Astrobiology Institute, and Agouron Institute to T.W.L and G.D.L.; Agouron Institute to B.G.; the Russian Foundation for Basic Research to A.M. and V.P.; AAPG Grants-in-Aid to C.A.P.; NSF-EAR-PDF to N.J.P.; the 973 Program grant and Moe grant of China to C.L. Sharad Master is gratefully acknowledged for providing shale samples from the Mwashya Formation. We thank Tom Algeo and two anonymous reviewers for useful comments that improved the manuscript. The authors dedicate this paper to H.D. Holland.Additional details
- Eprint ID
- 40724
- Resolver ID
- CaltechAUTHORS:20130819-152038265
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- EAR-0720362
- NSF
- NASA
- Agouron Institute
- Russian Foundation for Basic Research
- American Association of Petroleum Geologists
- 973 Program of China
- Ministry of Education (China)
- Created
-
2013-08-19Created from EPrint's datestamp field
- Updated
-
2021-11-10Created from EPrint's last_modified field