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Oxidative elemental cycling under the low O2 Eoarchean atmosphere
Robert Frei1,2, Sean A Crowe3, Michael Bau4
1Department of Geoscience and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark.
Scientific Reports
|February 12, 2016
Summary
Early Earth rocks reveal evidence of oxidative processes and possibly aerobic biology 3.8-3.7 billion years ago. This suggests reactive oxygen species existed in the Eoarchean atmosphere, influencing early geochemistry.
Area of Science:
- Geochemistry
- Paleobiology
- Early Earth conditions
Background:
- The Great Oxidation Event (around 2.4 Gyr ago) marked major atmospheric oxygenation.
- Geochemical evidence for oxidative weathering predates this event, extending back to 3.3-2.9 Gyr ago.
- Rocks from Isua, Greenland (3.8-3.7 Gyr old) provide insights into early Earth surface chemistry and the primordial biosphere.
Purpose of the Study:
- To investigate the presence and impact of oxidative processes in the Eoarchean surface environment.
- To analyze geochemical signatures in Isua banded iron formations (BIFs) for evidence of early oxidative cycling.
- To assess the potential for early aerobic biology under low-oxygen conditions.
Main Methods:
- Analysis of fractionated chromium (Cr) isotopes in Isua BIFs.
- Measurement of Uranium/Thorium (U/Th) ratios in Isua BIFs.
- Comparison of isotopic and elemental ratios with the igneous silicate Earth reservoir and contemporary crust.
Main Results:
- Fractionated Cr isotopes indicate oxidative Cr cycling occurred 3.8-3.7 Gyr ago.
- Elevated U/Th ratios suggest oxidative mobilization of Uranium.
- These findings point to reactive oxygen species in the Eoarchean surface environment.
Conclusions:
- Oxidative elemental cycling was active during the deposition of Isua BIFs.
- The presence of reactive oxygen species, even in a low-oxygen atmosphere, is indicated.
- These conditions may have supported the emergence of early aerobic biology.
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