The circulation of ferrous (Fe2+) and ferric (Fe3+) iron in the mantles of rocky planets determines the oxidation state of the mantle. In previous research study, the researchers showed that the Earths magma ocean was more enriched in Fe3+ than the present upper mantle, and therefore, extremely oxidizing (Kuwahara et al., 2023, Nat. A concern developed: How did the upper mantles oxidation state decrease to what we observe today? The atmosphere formed by the degassing of volatiles from such an extremely oxidizing mantle would have been rich in CO2 and SO2, thereby forming a Venus-like surface area environment.
The early Earths extremely oxidized mantle might have led to a Venus-like surface environment. Today state of the upper mantle might have been affected by metallic iron from products included after Earths formation.
How has the atmosphere and mantle oxidation state of the Earth changed?
The connection between a worlds interior and its surface plays an essential role in understanding the formation of a worlds surface area environment. The circulation of ferrous (Fe2+) and ferric (Fe3+) iron in the mantles of rocky planets determines the oxidation state of the mantle. This, in turn, influences the composition of volcanic gases and the mantles capability to keep volatiles, including crucial, life-essential aspects like hydrogen and carbon.
Identifying the circulation of Fe2+ and Fe3+ in the mantle right away after its development offers vital information about the surface area environment prior to life emergence and the beginnings of habitable planets.
The dark area in the lower part of the image reveals crystalized bridgmanite, and the dendritic texture in the upper part suggests satiated melt. Credit: Geodynamics Research Center, Ehime University
Previous Research and New Insights
In previous research, the scientists showed that the Earths magma ocean was more enriched in Fe3+ than the present upper mantle, and therefore, extremely oxidizing (Kuwahara et al., 2023, Nat. A question emerged: How did the upper mantles oxidation state decrease to what we observe today?
Condensation and Atmosphere Implications
The findings exposed that the condensation of bridgmanite, the most dominant lower mantle mineral, does not preferentially incorporate Fe3+ compared to existing together lava. If the Earths magma ocean was rich in Fe3+, this indicates that the early Earths upper mantle was likewise extremely oxidized. The atmosphere formed by the degassing of volatiles from such an extremely oxidizing mantle would have been abundant in CO2 and SO2, thereby forming a Venus-like surface environment.
Since the lava ocean crystallization process can not decrease the upper mantles oxidation state, the authors have actually proposed the decrease of the upper mantle by metal iron included in late-accreting materials after the formation of the Earth. Undoubtedly, the quantity of metallic iron provided by late accreting products constrained by the abundance of highly siderophile (iron-loving) elements in the Earths mantle is similar to that required to minimize the upper mantles oxidation state to today.
More geological restraints on the oxidation state of the mantle are required to test this hypothesis.
Reference: “Partitioning of Fe2+ and Fe3+ between bridgmanite and silicate melt: Implications for redox advancement of the Earths mantle” by Hideharu Kuwahara and Ryoichi Nakada, 25 May 2023, Earth and Planetary Science Letters.DOI: 10.1016/ j.epsl.2023.118197.
