X-ray Scattering Experiments on Melting and Equations of State of Candidate Compositions of Earth's Core

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The results expected from this project will improve our understanding of the temperature and chemical composition of Earth's core. Earth's core is known to be an iron-rich alloy, mostly molten but with a solid inner core. In addition to iron it contains approximately 5% nickel and approximately 10% of a lighter element, whose identity is uncertain but is likely a combination of oxygen, sulfur, silicon, and/or carbon. A more precise understanding of the composition of Earth's core is important to constrain our understanding of the chemical and physical processes that led to the formation of our planet. Furthermore, the temperature structure in the deep Earth is poorly known, and can be better constrained with more accurate measurements of the melting temperatures of candidate core compositions under the relevant pressure, temperature conditions. Accordingly, the aims of this project are to measure the melting temperatures and densities of iron alloys under the extreme pressure, temperature conditions that exist in Earth's core. The experimental results will be applied to place more accurate bounds on the temperatures and composition of Earth's core.The project has several specific experimental research goals. These include (1) Establishing melting temperatures in the ternary systems Fe-O-S, Fe-Si-S, and Fe-Si-O up to pressures appropriate in Earth's outer core; (2) Analyzing X-ray diffuse scattering measured from melts in these ternary systems to place constraints on their liquid densities; (3) Extending the equations of state of Fe3C and Fe3S to higher pressure and temperature conditions, to permit more precise thermodynamic treatment of S,C-bearing Fe-alloys, and more precise density-based constraints on the maximum content of S and C allowable in Earth's core. To achieve these goals the PI will perform synchrotron-based X-ray scattering experiments on samples that are pressurized and laser heated in a diamond anvil cell, reaching the extreme pressure, temperature conditions (in excess of 140 GPa and 4000 K) that exist in Earth's core. In parallel with these investigations, he will continue to develop experimental methods to improve the ability of his lab and others to investigate the material properties of Earth's core. These research projects will also serve as a platform on which the PI's training of graduate and undergraduate students will be trained in laboratory research and scientific pursuit.