Compositional Model for the Earth's Core

The remote setting of the Earth's core tests our ability to assess its physical and chemical characteristics. Extending out to half an Earth radius the metallic core constitutes a sixth of the planet's volume and a third of its mass. The boundary between the silicate mantle and the core is remarkable in that it is a zone of greatest contrast in Earth properties. The density increase across this boundary represents a greater contrast than across the crust–ocean surface. Our understanding of the core is based on very few pieces of direct evidence and many fragments of indirect observations. Direct evidence comes from seismology, geodesy, geo- and paleomagnetism, and, relatively recently, isotope geochemistry. Indirect evidence comes from geochemistry, cosmochemistry, and meteoritics; further constraints on the core system are gained from studies in experimental petrology, mineral physics, ab initio calculations, and evaluations of the Earth's energy budget. Feedback loops between all of these disciplines refine other's understanding of the Earth's core.