Geophysics of Iron in the Earth’s Core

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Located nearly 3000 km below the crust, the Earth’s core is the most remote region within our planet. Mainly composed of iron, the core’s outer shell is liquid while its most inner part, the inner core, is solid. The core plays a central role in the planet’s geomagnetism, dynamic processes, and thermal evolution. Here, the team conducts laboratory experiments at the extreme pressures and temperatures prevailing in Earth’s deep interior. They measure the properties of the iron-rich materials that make up the core, e.g., their deformation mechanisms and viscosity. These properties can be dramatically altered at core conditions. The results give insight into why seismic waves travel at different speeds through different parts of the inner core. They constrain how the Earth’s magnetic field is generated and unveil its past evolution. These outcomes are valuable to many researchers studying deep Earth’s processes: mineral physicists, seismologists, and geodynamicists. The project promotes technical advances useful across disciplines, in geoscience and materials science, and in the industry. It also provides support for a female graduate student, training for undergraduate students, and outreach toward K-12 students and the public.The project aims at characterizing key rheological properties of iron and iron-rich compounds and alloys at the extreme conditions of the deep Earth. Two fundamental questions are addressed: (1) What causes inner-core seismic anisotropy? (2) How does viscous dissipation in the outer core influence the evolution of the geodynamo? To address the first question, the team characterizes the dominant deformation mechanisms and strength of solid iron at high pressures and temperatures. The lattice preferred orientation that develops during iron crystallization is also measured. The goal is to understand how the alignment of elastically anisotropic iron crystals may be acquired during solidification or subsequent deformation (or both). To this aim, the researchers carry out static compression experiments in resistive and laser-heated diamond anvil cells. They perform in situ X-ray imaging and diffraction measurements at national synchrotron facilities. Addressing the second question requires measuring iron viscosity at core conditions. While traditional measurements are limited to lower pressures, the team benefit from new technical developments; these enable a path toward measuring the viscosity of iron dynamically compressed to outer core conditions. Thus the team carries out dynamic compression experiments and use novel X-ray diffraction and imaging techniques at the Materials at Extreme Conditions instrument at the Linac Coherent Light Source (SLAC) and the National Ignition Facility at Lawrence Livermore National Laboratory. These experiments represent new opportunities to leverage the considerable resources and expertise available at national laboratories and apply them to better understand the Earth.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.