Hydrogen distribution between the Earth?s inner and outer core

L Yuan and G Steinle-Neumann, EARTH AND PLANETARY SCIENCE LETTERS, 609, 118084 (2023).

DOI: 10.1016/j.epsl.2023.118084

Hydrogen, the most abundant element in the universe, has likely been incorporated into Earth's core due to its tendency to dissolve in iron at high pressure. Using machine-learning methods to overcome the length- and timescale limitations of quantum mechanical simulations and the difficulties in laboratory experiments, we characterize the phase behavior of superionic FeHx (x denotes nonstoichiometric compositions) in the Earth's core. We show that hexagonal packing of Fe is thermodynamically stable with and without H, and its melting temperature decreases by 700-900 K with 0.34 wt% H at the pressure of the inner core boundary. We further predict H partition coefficients between solid and liquid Fe as 0.50(3)-0.62(3), implying 1 and 33 times the mass of H in the ocean in the inner and outer core, respectively, which holds a key promise for H to explain seismic characteristics of the core.(c) 2023 Elsevier B.V. All rights reserved.

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