By Trey Hignight
As the Earth cools from the inside out, the molten outer core is slowly freezing. This is leading the solid inner core to grow at a rate of approximately 1 millimeter per year.
Using computer models of convection in the outer core in conjunction with seismology data, the researchers found the flow of heat at the boundary of the core and mantle depended on the overlying mantle. At times, the nature of the mantle is enough to force heat from the mantle back onto the core, leading to melting in places.