地球的磁场靠什么维持？

Earth's magnetic field shields us from deadly cosmic radiation, and without it, life as we know it could not exist here. The motion of liquid iron in the planet's outer core, a phenomenon called a "geodynamo," generates the field. But how it was first created and then sustained throughout Earth's history has remained a mystery to scientists. New work published in Nature from a team led by Carnegie's Alexander Goncharov sheds light on the history of this incredibly important geologic occurrence. Our planet accreted from rocky material that surrounded our Sun in its youth, and over time the most-dense stuff, iron, sank inward, creating the layers that we know exist today--core, mantle, and crust. Currently, the inner core is solid iron, with some other materials that were dragged along down during this layering process. The outer core is a liquid iron alloy, and its motion gives rise to the magnetic field. 

A better understanding of how heat is conducted by the solid of the inner core and the liquid in the outer core is needed to piece together the processes by which our planet, and our magnetic field, evolved--and, even more importantly, the energy that sustains a continuous magnetic field. But these materials obviously exist under very extreme conditions, both very high temperatures and very intense pressures. This means that their behavior isn't going to be the same as it is on the surface. 

"We sensed a pressing need for direct thermal conductivity measurements of core materials under conditions relevant to the core," Goncharov said. "Because, of course, it is impossible for us to reach anywhere close to Earth's core and take samples for ourselves."