Can Volcanism Build Hydrogen-Rich Early Atmospheres?

Abstract

Hydrogen in rocky planet atmospheres has been invoked in arguments for extending the habitable zone via N2-H2 and CO2-H2 greenhouse warming, and providing atmospheric conditions suitable for efficient production of prebiotic molecules. On Earth and Super-Earth-sized bodies, where H2-rich primordial envelopes are quickly lost to space, volcanic outgassing can act as a hydrogen source, provided it balances with the loss rate from the top of the atmosphere. Here, we show that both Earth-like and Mars-like planets can sustain atmospheric H2 fractions of several percent across relevant magmatic fO2 ranges. In general this requires hydrogen escape to operate somewhat less efficiently than the diffusion limit. We use a thermodynamical model of magma degassing to determine which combinations of magma oxidation, volcanic flux, and hydrogen escape efficiency can build up appreciable levels of hydrogen in a planet's secondary atmosphere. On a planet similar to the Archean Earth and with a similar magmatic fO2, we suggest that the mixing ratio of atmospheric hydrogen could have been in the range 0.2-3%. A planet erupting magmas around the Iron-Wustite (IW) buffer (i.e., ~3 log fO2 units lower than Archean Earth's), but with otherwise similar volcanic fluxes and H2 loss rates to early Earth, could sustain an atmosphere with approximately 10-20% H2. For an early Mars-like planet with magmas around IW, but a lower range of surface pressures and volcanic fluxes compared to Earth, an atmospheric H2 mixing ratio of 2-8% is possible. On early Mars, this H2 mixing ratio could be sufficient to deglaciate the planet. However, the sensitivity of these results to primary magmatic water contents and volcanic fluxes show the need for improved constraints on the crustal recycling efficiency and mantle water contents of early Mars.

Submitted with reviewer comments to Earth and Planetary Science Letters

References in corpus (9)

• Extreme Water Loss and Abiotic O${}_2$ Buildup On Planets Throughout the Habitable Zones of M Dwarfs
• Warming early Mars with CO2 and H2
• The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star
• Oxygen fugacities of extrasolar rocks: Evidence for an Earth-like geochemistry of exoplanets
• A Volcanic Hydrogen Habitable Zone
• Temporal evolution of the high-energy irradiation and water content of TRAPPIST-1 exoplanets
• A Lower Limit of Atmospheric Pressure on Early Mars Inferred from Nitrogen and Argon Isotopic Compositions
• Testing the Early Mars H2-CO2 Greenhouse Hypothesis with a 1-D Photochemical Model
• Warming Early Mars with Climate Cycling: The Effect of CO2-H2 Collision-induced Absorption

Cited by in corpus (14)

• Abundant atmospheric methane from volcanism on terrestrial planets is unlikely and strengthens the case for methane as a biosignature
• Growth and evolution of secondary volcanic atmospheres: I. Identifying the geological character of hot rocky planets
• Reduced atmospheres of post-impact worlds: The early Earth
• Low volcanic outgassing rates for a stagnant lid Archean Earth with graphite-saturated magmas
• A transmission spectrum of the sub-Earth planet L98-59~b in 1.1-1.7 $\mu$m
• Reduced late bombardment on rocky exoplanets around M-dwarfs
• Photochemical Runaway in Exoplanet Atmospheres: Implications for Biosignatures
• A mineralogical reason why all exoplanets cannot be equally oxidising
• Growth and Evolution of Secondary Volcanic Atmospheres: II. The Importance of Kinetics
• Prebiosignature Molecules Can Be Detected in Temperate Exoplanet Atmospheres with JWST
• A dry Venusian interior constrained by atmospheric chemistry
• Narrow loophole for H2-dominated atmospheres on habitable rocky planets around M dwarfs
• 3-D Global modelling of the early martian climate under a dense CO2+H2 atmosphere and for a wide range of surface water inventories
• A multispecies pseudoadiabat for simulating condensable-rich exoplanet atmospheres