An early geodynamo driven by exsolution of mantle components from Earth’s core

James Badro (1, 2) , Julien Siebert (1) , Francis Nimmo (3)

1 IPGP - Institut de Physique du Globe de Paris
2 EPFL - Ecole Polytechnique Fédérale de Lausanne
3 Department of Earth and Planetary Sciences [Santa Cruz]

Terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, stripping iron-loving elements from the silicate mantle to the metallic core1-3, and leaving rock-loving components behind. Here we performed experiments showing that at high enough temperature, Earth's major rock-loving component, magnesium oxide, can also dissolve in core-forming metallic melts. Our data clearly point to a dissolution reaction, and are in agreement with recent DFT calculations. Using core formation models5, we further show that a high-temperature event during Earth's accretion (such as the Moon-forming giant impact) can contribute significant amounts of magnesium to the early core. As it subsequently cools, the ensuing exsolution of buoyant magnesium oxide generates a substantial amount of gravitational energy. This energy is comparable to if not significantly higher than that produced by inner core solidification - the primary driver of the Earth's current magnetic field1. Since the inner core is too young to explain the existence of an ancient field prior to ~1 billion years, our results solve the conundrum posed by the recent paleomagnetic observation of an ancient field at least 3.45 Gyr old.

Domains: Earth and Planetary Astrophysics [astro-ph.EP]

James Badro, Julien Siebert, Francis Nimmo. An early geodynamo driven by exsolution of mantle components from Earth’s core. Nature, 2017, 536 (7616), pp.326-328. ⟨10.1038/nature18594⟩. ⟨insu-02135813⟩