Earth's magnetic field shields us from deadly cosmic radiation, without which life, as we know, could not exist here. But how it was first created and then sustained throughout Earth’s history has remained a mystery to scientists.

To explore the mystery, a team led by Alexander Goncharov, a research member in Institute of Solid State Physics (ISSP), Hefei Institutes of Physical Science, conducted a research which Sheds light on the history of this incredibly important geologic occurrence. And their research was published in Nature under the title Direct measurement of thermal conductivity in solid iron at planetary core conditions.

Our planet was composed of core, mantle, and crust. Currently, the inner core is solid iron and the outer core is a liquid iron alloy whose motion gives rise to the magnetic field. And how is the heat conducted by the solid of the inner core and the liquid in the outer core? It needs to piece together the processes of our planet, magnetic field, even more importantly, the energy that sustains a continuous magnetic field. Only under very extreme conditions, namely, both very high temperatures and very intense pressures, do these materials obviously exist, which means that their behavior is not 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.”

Given this, his team used a tool called a laser-heated diamond anvil cell to mimic planetary core conditions and to study how iron conducts heat under them. The diamond anvil cell squeezes tiny samples of material between two diamonds, creating the extreme pressures of the deep Earth in the lab. The laser heats the materials to the necessary core temperatures. Using this kind of lab-based mimicry, the team could study how the core propagates heat.

By research, they found that the ability of these iron samples to transmit heat matched with the lower end of previous estimates of thermal conductivity in Earth’s core—between 18 and 44 watts per meter per kelvin, in the units that scientists use to measure such things. These translates to predictions that the energy necessary to sustain the geodynamo have been available since very early in the history of Earth.

“Our measurement provides an estimation of the Fe thermal conductivity in the limits that allows to sustain the geodynamo and simultaneously making the heat losses consistent with a slow Earth’s cooling. ” Goncharov added.

Alexander Goncharov leads his team to set up state-of-art laboratories to study matters at extreme conditions of pressures and temperatures. Last year, he was honored 2015 People's Republic of China Friendship Award for his outstanding contribution to the promotion of international cooperation in scientific research.

Prof. Goncharov and post doctoral researcher are conducting laser heating experiments

under high pressure (Image by WANG Yuan)