56 The Earth's core

Abstract

This chapter provides an overview of the basic understanding of the Earth's core. It emphasizes on seismological accomplishments. Earth's core plays an important role in the formation and chemical differentiation of the planet, in global earth dynamics and earth rotation, and in the generation of the magnetic field. Earth's core was formed very early in Earth's history as heavy molten iron alloy migrated toward the center of the planet. As the Earth cooled and dissipated its internal heat toward the surface through mantle convection, molten iron began to solidify under enormous pressure to form the solid inner core. The fluid outer core is predominantly iron and the inner core is pure iron. The size of the outer core is more than a half of the Earth in radius and the size of inner core is about one fifth of the Earth in radius and slightly smaller than the moon. The gravitational energy release from the slow growth of the inner core as the liquid iron freezes drives the convection in the outer core, which generates the Earth's magnetic field. Also the inner core is elasticly anisotropic with the fast direction approximately parallel to the spin axis.