The inner core formed around one billion years ago; however the geological record shows a strong magnetic field has protected Earth for more than three billion years.
Researchers studying this conundrum have suggested that mineral exsolution (or precipitation) from the young Earth’s core could have powered an early geodynamo. A new paper from DCO Extreme Physics and Chemistry Scientific Steering Committee member James Badro (Institut de Physique du Globe de Paris, France) and colleagues, published in the journal Nature, suggests the key mineral in this scenario is magnesium oxide .
By combining laser-heated diamond anvil cell experiments and computational modeling techniques, Badro and colleagues analyzed whether magnesium oxide exsolution from a young, cooling core could have generated a geodynamo. The theory assumes that magnesium oxide was initially dissolved in core materials shortly after the planet formed. To test this assumption, the authors recreated core formation temperature and pressure conditions in the laboratory. They found that magnesium oxide could indeed have dissolved in the iron-rich materials of a young Earth’s core.
With these data in hand, the authors used sophisticated mathematical models to address whether crystallization of magnesium oxide out of the core could have generated a geodynamo. Only if they included modeling parameters accounting for a giant impact between young Earth and a second planetary body (Theia) could magnesium oxide crystallization generate enough energy to power the early geodynamo.
“Our data suggest that magnesium oxide crystallization could have powered a geodynamo on Earth as early as 3.5 billion years ago, if not earlier” said Badro. “It is noteworthy that driving a dynamo that early requires very high temperature conditions during Earth’s formation; a giant impact, such as the one that formed the Moon, could be that process. In a certain way, this most cataclysmic event in Earth’s 4.56 billion year history could also be the one responsible for making our planet habitable and a safe shelter for Life.”
Image credit: Joel Dyon, Institut de Physique du Globe de Paris