Though largely inaccessible, the geochemistry of Earth's mantle and core can be examined through a wide variety of approaches. Volume 2 focuses first on "remote" sensing using evidence from cosmochemical, seismic, petrologic and geochemical approaches. Mantle composition is then examined in detail through descriptions of mantle samples brought to Earth's surface through tectonic, volcanic, and volatile-outgassing processes. The volume concludes with examination of processes that modify the composition of the mantle and core including an early magma ocean, partial melting, element partitioning between minerals and melts, and physical mixing caused by plate subduction, mantle convection and mass exchange between mantle and core.