Abstract
The magma ocean was a important reservoir for Earth’s primary volatiles. Understanding the volatile fluxes between the early atmosphere and the magma ocean is fundamental for quantifying the volatile budget of our planet. Here we investigate the vaporization of carbon and hydrogen at the boundary between the magma ocean and the thick, hot early atmosphere using first-principles molecular dynamics calculations. We find that carbon is rapidly devolatilized, while hydrogen mostly remains dissolved in the magma during the existence of a thick silicate-bearing atmosphere. In the early stages of the magma ocean, the atmosphere would have contained significantly more carbon than hydrogen, and the high concentrations of carbon dioxide would have prolonged the cooling time of early Earth.
Highlights
Quantifying the total amount of volatiles stored in hidden reservoirs of Earth is crucial for our understanding of the global volatile cycle
Volatility of carbon At a density of about 2.6 to 2.7 g/cm3, similar to the lower-end density range of ultramafic lavas at present-day surface conditions, our simulations predict that carbonated pyrolite melt exists as an entirely polymerized melt without voids or cavities; all of the carbon is dissolved in the silicate melt phase
We find that carbon is rapidly devolatilized, while hydrogen remains mostly dissolved in the silicate melt at pressures corresponding to the shallow parts of a magma ocean under a thick silicate-bearing atmosphere
Summary
Quantifying the total amount of volatiles stored in hidden reservoirs of Earth is crucial for our understanding of the global volatile cycle. To estimate the volatile content of Earth’s interior, we must gain a better understanding of their fluxes throughout the history of our planet, starting with the global magma ocean stage [1]. According to the Giant Impact theory, a planetesimal collided with proto-Earth, melting and partially vaporizing the two bodies to create a disk from which present-day Earth and Moon subsequently formed [2,3,4,5]. A Mars-sized planetesimal obliquely collides with proto-Earth with a low impact velocity, creating a disk composed of a silicate melt interior surrounded by a vapor atmosphere. Heavier species in the atmosphere gradually condense into the magma ocean as the temperature continues to decrease
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