Experiments relating to Earth’s inner core raise questions about its age

Earth’s magnetic field (illustrated here) is sustained by liquid iron that is continuously churning in the planet’s outer core. Iron that crystallizes onto the solid inner core releases latent heat, which powers convection that drives Earth’s dynamo (see the article by Daniel Lathrop and Cary Forest, Physics Today, July 2011, page 40). But lately scientists have questioned whether that set of mechanisms has always provided the energy for Earth’s magnetic mojo. Simulations from a 2012 study suggested that iron has surprisingly high thermal conductivity under the extreme conditions that prevail in the core. The finding hinted that the core may export heat to the rocky mantle much faster than previously thought. If the core truly does lose heat so quickly, then it would have taken less than a billion years for the inner core to reach its current size. Some other process, then, would have had to...