2021).

Their model included seven atmospheric species (H2, H2O, CO2, CH4, CO, O2, and N2) and simulated the coupled evolution of the magma ocean solidification, and the resulting atmospheric spectral signatures.

From these simulations, Lichtenberg et al. (2021) showed that atmospheric composition strongly controls cooling timescales, with H2-dominated atmospheres producing the longest-lived magma oceans.

More recently, fully coupled models have emerged that include the regulation of the atmospheric inventory through feedbacks between the interior and atmosphere, and compute volatile outgassing and atmospheric composition during magma-ocean evolution.

These feedbacks arise from the coupled thermal evolution, whereby interior melting and degassing influence atmospheric opacity and cooling, which in turn affect the rate of interior solidification (Krissansen-Totton et al. 2021, 2024; Nicholls et al. 2024), these studies were compiled and reviewed by Lichtenberg & Miguel (2025); Lichtenberg et al. (2026).

Collectively, these studies demonstrate that the oxidation state of the magma ocean strongly controls planetary thermal evolution and atmospheric composition.

As long as the magma ocean remains in equilibrium with the atmosphere and the mantle volatile reservoir greatly exceeds that of the atmosphere, the interior composition effectively buffers the atmospheric redox state.

Recent work (Walbecq et al. 2025) suggests that outgassing may be limited by dynamical constraints on volatile exsolution and transport, so interior–atmosphere equilibrium is not guaranteed during magma ocean solidification.

Delayed degassing can therefore accelerate cooling and alter both atmospheric composition and mantle redox evolution.

Regardless of outgassing efficiency, the mantle’s baseline redox state is inherited from high-pressure differentiation, set by equilibrium between metallic iron and iron oxide (Wade & Wood 2005; Schlichting & Young 2022; Young et al. 2023; Schaefer et al. 2024; Cottrell et al. 2025).

Core-formation models further indicate that Earth’s mantle ended accretion in a relatively reduced state, around IW–2.0 i.e. two log units above the iron–wüstite buffer (Badro et al. 2015; Rubie et al. 2015).

Nevertheless, following Hirschmann (2012), recent experiments and molecular dynamics simulations suggested that high
pressures may stabilize ferric (Fe3+) over ferrous (Fe2+) iron in
silicate melts (Zhang et al. 2017; Armstrong et al. 2019; Deng et al. 2020; Kuwahara et al. 2023; Schaefer et al. 2024).

As a result, silicate melts equilibrated at depth may contain nonnegligible fractions of ferric iron even under globally reducing conditions.

During core formation, the segregation of metallic iron implies that a well-mixed mantle inherits the elevated Fe3+/Fe2+ ratios established at high pressure, resulting in higher effective oxidation states at lower pressures (Hirschmann 2022; Schaefer et al. 2024).

Chemical partitioning during magma ocean evolution further modifies mantle oxidation.

Fractional crystallisation enriches FeO in the residual melt (Elkins-Tanton et al. 2003; Elkins-Tanton 2008; Boukaré et al. 2018; Maurice et al. 2024), potentially forming a dense, iron-rich layer that can trigger mantle overturn (Elkins-Tanton et al. 2003; Boukaré et al. 2015, 2018).

Because ferric iron (Fe3+) is moderately incompatible relative to ferrous iron (Fe2+) (Canil & O’Neill 1996; Sorbadere et al. 2018), crystallisation drives their fractionation (McCanta et al. 2009).

This redistribution establishes evolving redox gradients, linking interior differentiation to the oxidation state of surface volatiles (Hirschmann 2012; Sossi et al. 2020).

Beyond its role in volatile and redox exchange, fO2 also directly modifies the melting behaviour of the mantle.

In this work, we distinguished between two physically distinct oxidation states: a deep-mantle oxygen fugacity, fOmelt
, which governs melting behaviour at high pressure, and a surface oxygen fugacity, fOsurf
, which controls near-surface outgassing and volatile speciation.

This distinction reflects an effective pressuredependence of fO2, consistent with experimental and theoretical results indicating that oxidation state may vary between deep and shallow mantle conditions.

Recent experiments by Lin et al. (2024) suggested that increasing fOmelt
depresses the solidus relative to reduced baseline measurements (Trønnes 2000; Trønnes & Frost 2002; Ishii et al. 2018).