UCLA

Earth's magnetic field has persisted for at least 3.4 billion years, yet the present-day core dynamo - driven by latent heat and compositional buoyancy from inner-core solidification - cannot have operated for most of that time, as the inner core is likely less than 1 billion years old. An alternative mechanism is required. A leading candidate is a basal magma ocean (BMO): a layer of iron-enriched silicate liquid that may have persisted at the base of the mantle for billions of years following Earth's magma-ocean stage. Whether this silicate dynamo operated, and whether analogous mechanisms generate fields in larger rocky exoplanets, depends on material properties that are poorly constrained or inaccessible to laboratory experiment. This dissertation examines the material properties governing magnetic field generation and BMO stability in rocky planets, from Earth to super-Earths, through first-principles calculations using density functional theory and ab initio molecular dynamics. The key quantities are the Fe-Mg distribution coefficient between silicate liquid and the dominant lower-mantle minerals bridgmanite and post-perovskite, which controls BMO gravitational stability; and the electrical conductivity, thermal conductivity, and Seebeck coefficient of iron-enriched silicate liquid and liquid iron, which govern whether the BMO and metallic core can sustain self-generating magnetic fields. We find that iron is strongly incompatible in bridgmanite and post-perovskite - the dominant lower-mantle phases in Earth and super-Earths, respectively - supporting gravitationally stable basal magma oceans in both. Conductivities of iron-enriched silicate liquid at BMO conditions exceed the threshold for dynamo action while permitting vigorous convection, establishing a silicate dynamo as a viable mechanism for Earth's early field. Transport properties of liquid iron from 2.5 GPa to over 3 TPa constrain core dynamo viability across the super-Earth mass range and yield the first calculation of the Seebeck coefficient at deep planetary conditions. These results form a unified, materials-physics framework for the magnetic histories of rocky planets.