Synchrotron studies are changing the understanding of the composition of the Earth’s core

In a work published in Advances in ScienceA team of researchers has determined a new pressure scale, which is important for understanding the formation of the Earth.

Using X-rays from a particularly powerful spectrometer at the Spring-8 Center of RIKEN they avoided some of the major approximations of previous work, finding that the front scale exceeded the pressure by more than 20% at 230 gigapascals (2.3 million atmospheres) – the pressure reached at the center of the Earth. This is like someone who runs a race that they think is 42 miles, only to find they have only run 34 miles. While 20% may seem like a modest adjustment, it has major implications.

An accurate pressure scale is important for understanding the composition of the Earth. In particular, core composition is hotly debated as it is important to understand our planet now, and to understand the evolution of the solar system in the past. While it is generally accepted that the core is iron, evidence from tracking the propagation of seismic waves from earthquakes suggests that the core contains lighter materials.

When the new scale was used to interpret the seismological model, the team found that the amount of light material in the inner core was about twice what was previously expected, and in fact the total weight of light material in the entire core was perhaps five times, or more, that of the Earth’s crust—the living layer. in it.

In the new work, the team, led by Alfred QR Baron of the RIKEN SPring-8 Center, and Daijo Ikuta and Eiji Ohtani of Tohoku University, used Inelastic X-ray Scattering (IXS) to measure the speed of sound of a sample of rhenium in the ground. pressure. A small sample of rhenium (The cell was placed in the spectrometer of the large IXS BL43LXU and small changes (~1 ppm) in the energy of X-rays scattered from the rhenium were carefully measured, allowing the researchers to determine the speed of sound. They determined both the pressure /length and shear/transverse resonances, and rhenium density.

A new study provides a direct relationship between rhenium concentration and depression. Baron says, “The abundance of rhenium at high pressure is accurate and quick to measure, and there are many facilities around the world where such measurements can be made. However, measuring the speed of sound is very difficult, and, at these pressures, is probably only possible using a spectrometer RIKEN at BL43LXU for SPring-8.” The team did the heavy lifting so that other scientists now use very simple density measurements to determine pressure.

As Ikuta, Ohtani, and Baron said, “When we used our new scale to interpret the behavior of metal cores under high pressure and compared them with the seismic model of the Earth, we found that the light objects hidden in the inner core are probably about twice what was previously expected .Similar changes, perhaps even greater in magnitude, can be expected when considering the composition of other planets. Our work also suggests a re-examination of the pressure dependence of almost all material properties that have been measured at the same or greater pressure. above the center of the Earth.”