Deep magma ocean formation set the oxidation state of Earth's mantle

The composition of Earth's atmosphere depends on the redox state of the mantle, which became more oxidizing at some stage after Earth's core started to form. Through high-pressure experiments, we found that Fe in a deep magma ocean would disproportionate to Fe plus metallic iron at high pr...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2019-08, Vol.365 (6456), p.903-906
Main Authors: Armstrong, Katherine, Frost, Daniel J, McCammon, Catherine A, Rubie, David C, Boffa Ballaran, Tiziana
Format: Article
Language:English
Subjects:
Atmosphere
Carbon dioxide
Composition
Degassing
Deposition
Diamonds
Earth
Earth atmosphere
Earth mantle
Iron oxides
Magma
Oceans
Organic chemistry
Oxidation
Redox properties
Species
Upper mantle
Valence
Volatile compounds
Volatiles
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Summary:The composition of Earth's atmosphere depends on the redox state of the mantle, which became more oxidizing at some stage after Earth's core started to form. Through high-pressure experiments, we found that Fe in a deep magma ocean would disproportionate to Fe plus metallic iron at high pressures. The separation of this metallic iron to the core raised the oxidation state of the upper mantle, changing the chemistry of degassing volatiles that formed the atmosphere to more oxidized species. Additionally, the resulting gradient in redox state of the magma ocean allowed dissolved CO from the atmosphere to precipitate as diamond at depth. This explains Earth's carbon-rich interior and suggests that redox evolution during accretion was an important variable in determining the composition of the terrestrial atmosphere.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.aax8376