Highlight of the importance of CO2 in the degassing of helium in the magma oceans of young planets

A collaboration between IPGP and the University of Oslo—partners within CircleU—offers new insights into the evolution of the early Earth’s atmosphere. Following the giant impact that led to the formation of the Moon, the Earth condensed as a hot molten sphere in the center of the protolunar disk. Volatile elements were trapped and condensed with heavier elements into a global magma ocean. As this ocean cooled and degassed, these volatiles played a crucial role in sculpting Earth’s secondary atmosphere.

Using state-of-the-art first-principles molecular dynamics calculations, the team simulated the behavior of carbon and helium in a pyrolite melt representative of the bulk silicate Earth composition, enriched with CO₂ and helium. Their findings reveal that the loss of volatiles is intricately linked to the pressure, temperature, and composition of the melt. Above approximately 25 kbar pressure, the melt forms a continuously polymerized network, fully dissolving both carbon and helium. However, as pressure decreases, nanoscale cavities—nanobubbles—form within the liquid, acting as reservoirs for gas-like species vaporized from the melt.

These simulations show that CO₂ enhances helium degassing by stabilizing the formation of nanobubbles and increasing their efficacy. The presence of carbon makes the melt less dense, facilitating the formation of channels through which helium can escape more readily. As carbon vaporizes, it not only assists in helium escape but also forms pathways that could have led to significant volatile losses from the magma ocean. This suggests an early Earth atmosphere richer in carbon and noble gases, and significantly hotter and thicker than previously estimated.