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