The oxygenation of Earth’s surface fundamentally altered global biogeochemical cycles and ultimately paved the way for the rise of metazoans at the end of the Proterozoic. However, current estimates for atmospheric oxygen (O₂) levels during the billion years leading up to this time vary widely. On the basis of chromium (Cr) isotope data from a suite of Proterozoic sediments from China, Australia, and North America, interpreted in the context of data from similar depositional environments from Phanerozoic time, we find evidence for inhibited oxidation of Cr at Earth’s surface in the mid-Proterozoic (1.8 to 0.8 billion years ago). These data suggest that atmospheric O₂ levels were at most 0.1% of present atmospheric levels. Direct evidence for such low O₂ concentrations in the Proterozoic helps explain the late emergence and diversification of metazoans.

Item Type:	Refereed Article
Keywords:	Precambrian, iron formation, atmosphere, chromium isotopes, animals
Research Division:	Earth Sciences
Research Group:	Geochemistry
Research Field:	Inorganic geochemistry
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the earth sciences
UTAS Author:	McGoldrick, P (Dr Peter McGoldrick)
ID Code:	97197
Year Published:	2014
Funding Support:	Australian Research Council (CE0561595)
Web of Science® Times Cited:	476
Deposited By:	Earth Sciences
Deposited On:	2014-12-05
Last Modified:	2017-11-02
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