The Geomagnetic Dynamo

Abstract The Earth’s magnetic field is generated in the liquid core by a self-sustaining dynamo mechanism. As the Earth cools, part of its heat passes through the liquid core by conduction, but the main mechanism of heat transfer is by convection due to buoyancy forces. Thermal convection results from temperature-related density differences in the liquid; compositional convection is caused by light elements released during solidification of the liquid iron alloy at the surface of the inner core. The buoyant electrically conducting liquid interacts with the Coriolis force due to the Earth’s rotation and is forced to flow in helical columns, twisting the field lines of the magnetic field inside the core. The pattern of the magnetic field at the core–mantle boundary reflects these interactions. The timing of nucleation of the inner core and the nature of the magnetic field in the early Earth are still a matter of conjecture.