Numerical Modeling of Thermo-chemical Convection in Earths Core and Implications for Geodynamo Evolution

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Earth’s magnetic field acts as a “magnetic shield” by deflecting high energy particles and keeping the surface habitable for life. Evidence for the existence of Earth’s magnetic field goes back billions of years, and may span the entire age of our planet. Despite its ever-presence, the way the magnetic field has been maintained by fluid motion in Earth’s liquid outer core for so long remains a mystery. In fact, the timing of the most dramatic event in the core’s history, the solidification of the inner core, is not known. The first solidification of the iron-rich alloy at the center of the Earth is expected to release a large pulse of energy that is manifested as a rapid change in the magnetic field at Earth’s surface. So far no clear signature of inner core solidification has been found in the rock magnetic record. This project will address this conundrum by developing a numerical simulation that models the effects of inner core solidification and its continued growth over time on the surface magnetic field. The impact of this modeling effort will go well beyond Earth’s core: a better understanding of the magnetic effects of core solidification can provide insight into how Earth has cooled over time and whether the ancient surface environment was protected by a magnetic shield that allowed life to flourish.The goal of this project is to implement additional buoyancy fields in a community dynamo code, investigate how thermal and compositional buoyancy fields couple together in driving convection and dynamo action in Earth’s core, and predict how the geomagnetic field has behaved since inner core nucleation. In Earth’s core the thermal and compositional buoyancy fields are coupled at the inner core boundary where thermal cooling drives solidification and releases light elements (composition) that combine together to drive convective flows that induce a global magnetic field. This thermo- chemical boundary coupling has not previously been explored in direct numerical simulations of the dynamo, and will shed new light on how the geomagnetic field was influenced by the growth of the inner core. The project plan is to (1) perform further development of an existing dynamo code (Rayleigh) to include an arbitrary number of scalar buoyancy fields, each with individual boundary conditions and diffusivities, and (2) perform a systematic numerical investigation of the physics of two interacting and boundary-coupled buoyancy fields undergoing rotating convection and dynamo action. The modeling will provide valuable new insight into how Earth’s core convects and how the growth of the inner core has influenced the geodynamo over Earth history. The project will fund a postdoc to develop the code, numerically investigate coupled thermo-chemical dynamo action, and apply these results to the evolution of the geodynamo.This project is co-funded by a collaboration between the Directorate for Geosciences and Office of Advanced Cyberinfrastructure to support AI/ML and open science activities in the geosciences.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.