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A shale-hosted Cr isotope record of low atmospheric oxygen during the Proterozoic

Devon B. Cole, Christopher T. Reinhard, Xiangli Wang, Bleuenn Gueguen, Galen P. Halverson, Timothy Gibson, Malcolm S. W. Hodgskiss, N. Ryan McKenzie, Timothy W. Lyons and Noah J. Planavsky
A shale-hosted Cr isotope record of low atmospheric oxygen during the Proterozoic
Geology (Boulder) (July 2016) 44 (7): 555-558


The emergence and expansion of animal life on Earth represents a dramatic shift in the structure and complexity of the biosphere. A lack of firm constraints on surface oxygen levels during the mid-Proterozoic has resulted in heated debate as to whether the rise and earliest diversification of animals was directly linked to a change in environmental oxygen levels or, instead, simply reflects the timing of innovations in gene expression and developmental regulation and was independent of a direct environmental trigger. Here, we present chromium (Cr) isotope data from marine black shales that provide evidence for minimal Cr oxidation throughout the mid-Proterozoic leading up to the diversification of eukaryotes and the rise of animals during the late Neoproterozoic. This observation requires very low background oxygen levels (<1% of present atmospheric levels). Accepting previously proposed estimates of pO (sub 2) levels needed to induce Cr isotope fractionation, our data provide support for the persistence of an Earth system in which baseline atmospheric pO (sub 2) would have been low enough to inhibit the diversification of animals until ca. 800 Ma. More generally, evidence for a delayed rise of atmospheric oxygen strongly suggests that environmental factors have played a fundamental role in controlling the emergence and expansion of complex life on Earth.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 44
Serial Issue: 7
Title: A shale-hosted Cr isotope record of low atmospheric oxygen during the Proterozoic
Affiliation: Yale University, Department of Geology and Geophysics, New Haven, CT, United States
Pages: 555-558
Published: 201607
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 34
Accession Number: 2016-070846
Categories: Isotope geochemistryStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2016185
Illustration Description: illus.
Secondary Affiliation: Georgia Institute of Technology, USA, United StatesMcGill University, CAN, CanadaUniversity of California at Riverside, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201634
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