Silicate and Thermoelectric Dynamos in the early Earth

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

The magnetic field is an ancient feature of our planet, dating back to at least 3.5 billion year ago. This magnetic field would have shielded the early Earth, allowing early life to flourish. Yet how the ancient field was produced is unknown. The mechanism that we think is responsible for producing the field today and for the last one billion years: a dynamo powered by freezing the liquid outer core to form the growing solid inner core, could not have operated because the core was too hot early on. But the core may not be the only metallic region in the early Earth. The early Earth may have been hot enough to maintain a deep molten portion of the rocky mantle: a basal magma ocean. Recent results show that the electrical conductivity of the deep mantle, in molten form, is much greater than previously thought. These findings highlight the need for a much greater understanding of how molten rock becomes metallic at high pressure and temperature, and the investigation of two hypotheses for the origin of the ancient field: a silicate dynamo, hosted in the basal magma ocean, and a thermoelectric dynamo produced by currents across the core-mantle boundary, in a mechanism akin to the operation of a thermocouple. Research under this award will test these hypotheses by predicting key material properties using first-principles quantum-mechanical simulations. This research will enrich our understanding of the early Earth and impact many fields of study, including the dynamical and chemical evolution of the interior, as well as surface conditions and the early evolution of life. The research will advance our understanding of the fundamental physics governing electron transport at extreme conditions, and help to guide the design of future experiments. The project will support the training of a graduate student in advanced materials simulation and applications to geophysics. The results of this research will subject two hypotheses for the generation of the early magnetic field to fundamental tests by predicting ab initio the electron transport properties of silicate liquids at high pressure: a silicate dynamo, hosted in the basal magma ocean, and a thermoelectric dynamo produced by currents across the core-mantle boundary. The project will compute from first principles the key physical properties governing the possible existence of silicate and thermoelectric dynamos in the Earth. The focus is on the role of pressure, temperature, and composition on the values of the electrical conductivity, the electronic contribution to the thermal conductivity, and the Seebeck coefficient. The electrical conductivity is important for understanding the possible existence and behavior of a silicate dynamo hosted in the basal magma ocean. The thermal conductivity is important for understanding thermal evolution and sets the adiabatic heat flux that must be exceeded for the silicate dynamo to operate. The Seebeck coefficient is key to the operation of a thermoelectric contribution to the dynamo. The simulations, based on density functional theory and the Kubo-Greenwood theory of electron transport, will provide fundamental insight into the physics governing electron transport in liquids, and will make direct contact with experimental measurements via the optical reflectivity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.