Nebular atmosphere to magma ocean: A model for volatile capture during Earth accretion

The origin and abundance of mantle volatiles present major questions for Earth's evolution. Here we quantify volatile capture from an atmosphere derived from the solar nebula during accretion, using a boundary layer Model of magma ocean dynamics coupled to a nebular atmosphere model adapted to Earth formation. Key elements include (i) nebular atmosphere winds based on scaling laws for deep rotating fluids; (ii) water production at the magma surface; and (iii) gas transfer between magma and atmosphere based on the systematics of air-sea gas exchange by wind and diffusion. Provided the Earth accreted to 30% or more of its final mass in the presence of the solar nebula, the mantle is expected to have ingassed several ocean mass equivalents of water plus hydrogen, along with hundreds of petagrams of helium-3 and other light noble gases. In contrast to light gases, nebular ingassing does not provide the mantle with enough heavy noble gases to account for their present-day atmosphere abundances. Our model also predicts that thermal insulation by the nebular atmosphere led to very hot conditions in Earth's interior during accretion, with peak temperatures above 6000 K at the core-mantle boundary and possible dynamo conditions in the Early Hadean.