Coupled evolution of Earth's H2-rich proto-atmosphere and oxidized magma ocean: Efficient H2O production through dissolved H2 transport and atmospheric buffering of the magma ocean redox state

Abstract

Giant impacts during Earth's final accretion likely generated global magma oceans, where the disproportionation of Fe^2+ at lower-mantle pressures and segregation of the resulting metallic iron into the core could have oxidized the magma ocean. Earth may nevertheless have had an H2-rich proto-atmosphere in chemical disequilibrium with the magma ocean, but the chemical coupling between this atmosphere and an oxidized magma ocean remains poorly constrained. Here we develop a coupled atmosphere-interior evolution model that includes diffusive transport in the boundary layer between the magma ocean and atmosphere, redox reactions in the melt, partitioning of oxide components and H2O among coexisting phases, and planetary cooling through a proto-atmosphere, with metallic iron produced by Fe^2+ disproportionation removed into the core as it forms. Atmospheric H2 transport into the magma ocean and subsequent H2O production become more efficient with increasingly frequent boundary layer renewal driven by buoyant overturn of dense melt cooled at the surface, allowing the atmosphere and magma ocean to chemically equilibrate within ~10^4 yr when the magma ocean is sufficiently deep and hot to extend into the lower mantle. Redox exchange with the atmosphere buffers the solidification-driven redox evolution of the magma ocean, preventing extreme oxidation or reduction of the coupled system. These results suggest that the coupled evolution could have contributed to early Earth's water inventory while maintaining a reducing H2-rich atmosphere.

arXiv commentPublished in The Planetary Science Journal

References in corpus (27)

• Photochemistry in Terrestrial Exoplanet Atmospheres I: Photochemistry Model and Benchmark Cases
• Transient reducing greenhouse warming on early Mars
• ExoCross: a general program for generating spectra from molecular line lists
• Water loss from terrestrial planets with CO2-rich atmospheres
• Chemistry of atmospheres formed during accretion of the Earth and other terrestrial planets
• Predictions of the atmospheric composition of GJ 1132b
• Condensation-inhibited convection in hydrogen-rich atmospheres: Stability against double-diffusive processes and thermal profiles for Jupiter, Saturn, Uranus, and Neptune
• Retention of water in terrestrial magma oceans and carbon-rich early atmospheres
• Vertically resolved magma ocean-protoatmosphere evolution: H${}_2$, H${}_2$O, CO${}_2$, CH${}_4$, CO, O${}_2$, and N${}_2$ as primary absorbers
• What factors affect the duration and outgassing of the terrestrial magma ocean?
• Redox hysteresis of super-Earth exoplanets from magma ocean circulation
• Hydrogen isotopic evidence for early oxidation of silicate Earth
• The erosion of large primary atmospheres typically leaves behind substantial secondary atmospheres on temperate rocky planets
• A cool runaway greenhouse without surface magma ocean
• A 3D picture of moist-convection inhibition in hydrogen-rich atmospheres: Implications for K2-18 b
• Effect of mantle oxidation state and escape upon the evolution of Earth's magma ocean atmosphere
• Less effective hydrodynamic escape of H${}_2$-H${}_2$O atmospheres on terrestrial planets orbiting pre-main sequence M dwarfs
• Inefficient water degassing inhibits ocean formation on rocky planets: An insight from self-consistent mantle degassing models
• Magma ocean evolution at arbitrary redox state
• The effect of a small amount of hydrogen in the atmosphere of ultrahot magma-ocean planets: atmospheric composition and escape
• Evolution and Spectral Response of a Steam Atmosphere for Early Earth with a coupled climate-interior model
• Volatile atmospheres of lava worlds
• Redox evolution of the crystallizing terrestrial magma ocean and its influence on atmosphere outgassing
• Suppression of hydrodynamic escape of an H2-rich early Earth atmosphere by radiative cooling of carbon oxides
• Experiments reveal extreme water generation during planet formation
• Building Wet Planets through High-Pressure Magma-Hydrogen Reactions
• Self-Shielding Enhanced Organics Synthesis in an Early Reduced Earth's Atmosphere