The study of the Earth's deep interior is one of the most fascinating fields of modern research. It expands our knowledge about the world in which we live and provides clues for understanding processes that have shaped our planet and determine phenomena that we observe on the surface of the Earth such as the magnetic field of the Earth, volcanism, earthquakes, etc. Our understanding of the deep Earth comes from a number of different sources, including: 1) geophysical observations, mainly seismology and geomagnetic observations , 2) mineral physics, 3) numerical modeling of the Earth?s dynamics and energetics, 4) geochemistry and cosmochemistry, and 5) direct (but, unfortunately, limited) evidence from the deep mantle from inclusions in diamonds.

Mineral physics provides information about the physical properties of Earth forming minerals, their dependence on temperature and composition, and phase diagrams of mineral systems. Mineral physics information is used to explain seismic discontinuities, deduce the composition and temperature inside the Earth, interpret the origins of seismic anisotropy. While experimentally it is possible to reach conditions of the Earth's innermost core, such studies are extremely complicated and have significant uncertainties in the measurements of pressure, temperature, and physical properties, many of which can not yet even be measured at all. In this situation, theoretical simulations based on quantum mechanics and making no assumptions about the nature of the material, have already proven their utility in Earth sciences, in particular, in combination with experiment. Among many important advances made using quantum-mechanical calculations are the establishment of the crystal structure of MgSiO3 perovskite, discovery and characterization of MgSiO3 post-perovskite, and the determination of the melting curve of iron. The discovery of post-perovskite has provided, for the first time, a simple convincing explanation for seismic anomalies found in the D" layer of the Earth mantle and uncovered fascinating insights into the structure, dynamics, and evolution of our planet. For instance, it explained the unusually large topography of the D" discontinuity and showed that the D" layer is growing with time as the Earth cools down. The existence of the post-perovskite phase transition in the deep mantle has been shown to lead to important geodynamical consequences. The large contrast of rheological properties between perovskite and post-perovskite may also have important geodynamical implications. The post-perovskite phase transition provided tighter constraints on the temperature profile in the mantle, the heat flow from the core into the mantle, and explained the double discontinuity found near the boundary with the core. The melting curve of iron, on the other hand, helped researchers to constrain the temperature profile in the Earth's core. Despite these breakthroughs, Earth's inner core and core-mantle boundary remain mysterious regions with major unsolved questions. The present project aims at clarifying these questions. Ths investigators will apply the most advanced and recently developed tools in computational physics - in particular, evolutionary crystal structure prediction (Oganov, Glass, 2006) to address outstanding problems related to the inner core and core-mantle boundary region. (i) From crystal chemistry of alloys to the chemistry of the inner core. Usually, compositional models of the inner core start from equations of state of FeSi, FeS or Fe3S, Fe1-xO, Fe3C or Fe7C3, and FeH - which are assumed to be the stable compounds in the corresponding binary systems. Except FeSi, none of these compounds were proved (either experimentally or theoretically) to be stable at the actual conditions of the inner core. The actually stable compounds may have different chemistry, coordination numbers, density and elasticity, and this may lead to serious changes in compositional models of the inner core. (ii) Properties of alloys in the inner core. Once we predict the stable compositions and structures, equations of state and elastic constants will be computed taking into account the effects of pressure and temperature. Anomalous anisotropy and high Poisson ratio may then be perhaps explained by the properties of iron alloys. (iii) Reaction at the core-mantle boundary: what could be its products? There are proposals of various chemical reactions occurring at the core-mantle boundary. Such a reaction could have important geophysical implications, and the PI would like to approach this possibility theoretically/computationally by exploring chemical equilibria in the relevant multicomponent system(s). While direct exploration of all possible reactions in this system is overwhelmingly difficult, new computational tools may enable rapid exploration.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Robin Reichlin
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State University New York Stony Brook
Stony Brook
United States
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