Iron in Earth's Core Behaves Strangely

Iron is the most important element in our planet's core, that much is known. What is still a mystery is how it behaves under the extreme pressure and temperature levels inside Earth. Thanks to a new series of experiments, scientists now have a much deeper understanding of what is happening down there.

One of the reasons why understanding Earth's iron core is so important is that this may provide us with hints as to what happened when the planet first formed, way back when the Sun was still a new star.

At the same time, the conclusions could also reveal why the planetary core behaves the way it does. The new investigation was conducted by a team at the California Institute of Technology (Caltech).

Mineral-physics researchers here developed a series of extremely high-pressure experiments, which allowed them to investigate how iron behaved in conditions similar to those encountered inside Earth.

The experimental setup was fairly easy to put together. Scientists took tiny iron samples, and then compressed them between two diamond anvil cells. The DAC were meant to replicate the huge pressures iron is subjected to in the inner core.

The cells were able to apply a level of pressure that was 1.7 million times the pressure we are subjected to at the surface of the planet. This is the equivalent of 171 Gigapascals. The work was carried out at the Argonne National Laboratory's (ANL) Advanced Photon Source (APS).

“Pinpointing the properties of iron is the gold standard – or I guess 'iron standard' – for how the core behaves. That is where most discussions about the deep interior of the earth begin. The temperature distribution, the formation of the planet – it all goes back to the core,” Jennifer Jackson explains.

The expert holds an appointment as an assistant professor of mineral physics at Caltech, and is also a coauthor on the new study. The paper appears in the December 20 issue of the esteemed scientific journal Geophysical Research Letters.

“The vibrational properties that we were able to measure at extraordinarily high pressures [at the APS] are unprecedented. These pressures exist in the earth’s outer core, and are very difficult to reproduce experimentally,” Jackson explains.

The paper was entitled “Grüneisen parameter of hcp-Fe to 171 Gpa.” The team was funded by Caltech, the National Science Foundation, and the US Department of Energy.