Properties and evolution of the Earth's core and geodynamo
We review recent advances in the study of the Earth's iron core, focusing on three areas: the properties of the core forming materials, the manner in which core motions generate the Earth's magnetic field (the dynamo) and the evolution of both the core and the dynamo. Ab initio computer simulations of the behaviour of iron alloys under core conditions suggest that the inner (solid) and outer (liquid) core contain 8% sulphur/silicon, and 8 10% sulphur/silicon plus 8 13% oxygen, respectively. The inner core boundary for these materials is at ~5500 K. Although computer simulations of the dynamo lack sufficient resolution to match likely terrestrial parameter values, such models can now reproduce the spatial and temporal behaviour of the observed magnetic field. The present day dynamo occurs because the mantle is extracting heat (at a rate of 9+ 3 TW) the resulting inner core growth drives core convection and implies a young inner core age <1.5 Gyr) A long lived dynamo requires rapid core cooling, which tends to result in an inner core larger than that observed. A possible solution to this paradox is that radioactive potassium may reside in the core. We also briefly review the current state of knowledge for cores and dynamos in other planetary bodies.