Summary
We will elucidate how the Earth’s core plays a key role in making the planet active and habitable, by examining the crystallisation sequence of an impure liquid core and its influence on the generation of magnetic fields. Earth’s core consists of an Fe alloy, but with small amounts of impurities which produce chemical differentiation upon core crystallisation, and hence control the strength of core convection by chemical buoyancy. Silicon and oxygen are likely the major impurities in the ancient core as a consequence of metal-silicate interaction in the magma ocean early in Earth’s history. This project will determine the crystallisation sequence of Fe-Si-O core liquids with a unique approach: constructing a thermodynamic model under high pressure (P) and temperature (T) conditions based on very precise laboratory measurements that were not previously possible. The constructed model will enable us to calculate the liquidus phase relations and isentropic P-T profiles for an assumed bulk composition. From the results, we will determine how a liquid core evolved its composition through chemical differentiation upon cooling, either precipitating SiO2 or demixing, in addition to inner core crystallisation. We will then employ geodynamic calculations, using the obtained physical parameters for core materials, to determine how the chemical differentiation processes could have powered the geodynamo as a function of the bulk Si/O ratio and thermal conductivity for iron. By comparing thus-predicted geodynamo history with the recorded paleomagnetic data of field intensity, we will report a consistent set of the Si/O ratio in the ancient core, iron conductivity, and paleomagnetic data. The geodynamo should have influenced the habitability of the Earth, as the generated magnetic field protects surface life from the harmful solar wind. We will, therefore, provide a holistic scenario of cooling processes of the core and their link to the mechanism which keeps the Earth habitable. New insight into the nature of the core drives understanding of such fundamental Earth processes through time, and is pivotal to understanding how the Earth functions, including its surface environment and its ability to sustain life.
This project is supported by the Natural Environment Research Council
[Grant No. NE/W005832/1].
