title: Oxidative elemental cycling under the low O2 Eoarchean atmosphere.
abstract: The Great Oxidation Event signals the first large-scale oxygenation of the atmosphere roughly 2.4 Gyr ago. Geochemical signals diagnostic of oxidative weathering, however, extend as far back as 3.3-2.9 Gyr ago. 3.8-3.7 Gyr old rocks from Isua, Greenland stand as a deep time outpost, recording information on Earth's earliest surface chemistry and the low oxygen primordial biosphere. Here we find fractionated Cr isotopes, relative to the igneous silicate Earth reservoir, in metamorphosed banded iron formations (BIFs) from Isua that indicate oxidative Cr cycling 3.8-3.7 Gyr ago. Elevated U/Th ratios in these BIFs relative to the contemporary crust, also signal oxidative mobilization of U. We suggest that reactive oxygen species were present in the Eoarchean surface environment, under a very low oxygen atmosphere, inducing oxidative elemental cycling during the deposition of the Isua BIFs and possibly supporting early aerobic biology.
authors: Department of Geoscience and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark.|Nordic Center for Earth Evolution, NordCEE, Denmark.
authors: Robert
authors: R
authors: Frei
authors: Departments of Microbiology and Immunology, and Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, Canada.
authors: Sean A
authors: SA
authors: Crowe
authors: Department of Physics and Earth Science, Jacobs University Bremen, Bremen, Germany.
authors: Michael
authors: M
authors: Bau
authors: Department of Earth and Environmental Science, University of Windsor, Canada.
authors: Ali
authors: A
authors: Polat
authors: Department of Geology, University of Kansas, Lawrence, KS, USA.
authors: David A
authors: DA
authors: Fowle
authors: Department of Geoscience and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark.
authors: Lasse N
authors: LN
authors: Døssing