O oxigênio estava presente na atmosfera há muito mais tempo do que antes presumido

sexta-feira, fevereiro 19, 2016

Oxidative elemental cycling under the low O2 Eoarchean atmosphere

Robert Frei, Sean A. Crowe, Michael Bau, Ali Polat, David A. Fowle & Lasse N. Døssing

Scientific Reports 6, Article number: 21058 (2016)

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Geochemistry | Palaeoclimate

Received: 19 June 2015 Accepted: 02 December 2015

Published online: 11 February 2016


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.

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