Unlocking Earth's deep secrets

Abstract

The most extreme boundary on Earth lies not at its surface, but nearly halfway to the centre of the planet at a depth of around 2900km. This is the boundary between Earth's mantle and core; it divides the solid, sluggish mantle from the dense, liquid, turbulently convecting outer core. The outer core consists of an iron alloy, while the mantle is dominantly rocky silicates. The core-mantle boundary formed early in Earth's history as dense iron sank to the centre forming the core. Since then, the boundary has played an important role in the evolution and dynamics of our planet. The heat flux across it cools the outer core, causing convection and driving the geodynamo. Lateral and temporal variations in the heat flux can affect the stability of the geodynamo, resulting in a time-varying magnetic field. The flux across the core-mantle boundary also heats the base of the mantle, where upwelling mantle plumes form, which cause intraplate hotspot volcanism at the surface. This mechanism explains, for example, Hawaiian volcanism. Chemical exchange may also occur, although the direction and nature of material flux are debated.