The Earth's inner core and the geodynamo: Determining their roles in the Earth's history



Inge Lehmann, the Danish seismologist who died recently at the age of 105, deduced nearly 60 years ago that the Earth has a solid inner core (IC). Interest in the IC has continued since then with particular focus on the role it may play in the generation and maintenance of the Earth's magnetic field. A fundamental question concerning the Earth's magnetic field is what drives the geodynamo. The two main contenders are thermal convection and compositional convection. Braginsky [1963] suggested that freezing of material at the inner core boundary (ICB) would separate a heavy fraction (mainly Fe) leaving behind a lighter liquid fraction in the outer core (OC) that would be buoyant leading to compositionally driven convection. Since then it has generally come to be accepted that gravitational convection dominates over thermal convection in the OC.