title: Earth history. Low mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals.
abstract: 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.
authors.affiliation: Department Geology and Geophysics, Yale University, CT, USA. noah.planavsky@yale.edu chris.reinhard@eas.gatech.edu.
authors.forename: Noah J
authors.initials: NJ
authors.lastname: Planavsky
authors.affiliation: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, GA, USA. noah.planavsky@yale.edu chris.reinhard@eas.gatech.edu.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Reinhard
authors.affiliation: Department Geology and Geophysics, Yale University, CT, USA. Department of Geology, University of Illinois, Champaign, IL, USA.
authors.forename: Xiangli
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Earth Science, Carleton University, Ottawa, ON, Canada.
authors.forename: Danielle
authors.initials: D
authors.lastname: Thomson
authors.affiliation: Centre for Ore Deposit and Exploration Science, University of Tasmania, TAS, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: McGoldrick
authors.affiliation: Geological Survey of Canada, Ottawa, ON, Canada.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Rainbird
authors.affiliation: Department of Geology, University of Illinois, Champaign, IL, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Johnson
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
authors.forename: Woodward W
authors.initials: WW
authors.lastname: Fischer
authors.affiliation: Department of Earth Sciences, University of California, Riverside, CA, USA.
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Lyons
mesh_terms: D000818:Animals; D001272:Atmosphere / Q000737:chemistry*; D005075:Biological Evolution; D002859:Chromium Isotopes / Q000737:chemistry; D018534:Earth, Planet; D019015:Geologic Sediments / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis*; D010163:Paleontology
chemical_list: D002859:Chromium Isotopes; D010100:Oxygen