Earth’s structure, lower mantle

Earth’s lower mantle represents the largest volume of any depth shell on Earth. It is unique in that its chemistry, structure, dynamics, and evolution represent a time-integrated effect of the chemistry and dynamics of the surface (litho-sphere, asthenosphere) and lowermost mantle (D⁰⁰, ULVZ, CMB) boundary layers. The degree to which the lower mantle is recycled into the upper mantle depends upon many poorly known convective parameters, such as the viscosity and viscous coupling of descending slabs, as well as material properties, such as the nature and origin of dense deep mantle chemically distinct piles. Future work of improved seismic imaging coupled with continued advancements in other deep Earth disciplines, such as geodynamics, mineral physics, and geochemistry, will greatly help to reduce uncertainties in our understanding of Earth’s evolutionary pathway, and present-day structure and dynamical state.