Earth science: Formation of the Earth’s magnetic field

Insights into how the Earth’s early magnetic field was produced are provided in a modelling study published in Nature Communications.

The Earth’s magnetic field has operated for at least the last 3.4 billion years, but its origins are unclear. Today it is produced by a dynamo in the metallic iron-rich liquid outer core; however, this process would have been difficult to sustain in the early Earth because the core could not cool rapidly enough. At this time the early core was surrounded by a molten silicate layer (a basal magma ocean), but previous electrical conductivity measurements for silicate liquids suggest these compounds could not generate a dynamo.

Lars Stixrude and colleagues performed a series of simulations to predict the electrical conductivity of a silicate liquid in conditions similar to those of the basal magma ocean of the early Earth. The authors found that at the temperature and pressure conditions predicted in this ocean, the electrical conductivity of the silicate is sufficient to sustain a dynamo. Based on their results, they computed magnetic field strengths and found that they were similar to those observed in the Archean (approximately 4 to 2.5 billion years ago) paleomagnetic record. They conclude that the early magnetic field was produced by the basal magma ocean and suggest that silicate dynamos may be present in other terrestrial bodies in the universe.