Nature of the Lower Mantle

The dynamics of the Earth's lower mantle, the largest continuous region of the interior, plays a major role in controlling the thermal evolution of the planet. The lower mantle extends from 660-2890 km depth (24-136 GPa) and is inaccessible by direct observation. Observations of variations in the velocity of seismic waves with position (heterogeneity) and with propagation direction (anisotropy), promise a revolution in our understanding of the dynamics of this important layer. However, this expectation can only be fulfilled by comparable advances in our understanding of the properties of the primary constituents of the lower mantle. These allows the conversion of lateral variations in velocity to lateral variations in temperature and composition, placing constraints on Earth's thermal state and on the pattern of mantle convection. First principles computations have led to major advances in our understanding of elasticity and seismic wave propagation as well as phase transitions at the high pressures and temperatures of the mantle. However, it has just started scratching the surface of the formidable challenges related to the fact that these phases are solid solutions involving strongly correlated end members that may undergo spin transitions under typical mantle pressures. This project consists in tackling these challenges. (Wentzcovitch, de Gironcoli, Karki, and Allen)

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