Redefining Earth’s Core: Synchrotron Reveals Hidden Light Material

A new pressure scale was determined using high-resolution x-rays at RIKEN’s SPring-8 Center. The old scale was found at a pressure 20% higher than the levels found in the Earth’s core. The implications of the new scale are huge, with revelations that the inner core has twice as much light as previously thought.

Researchers revealed a more precise scale of pressure using high-resolution x-rays, revealing the inner core is twice as luminous as previously predicted. Their methodology provides a simple method for future stress measurements.

In a study published on September 8 in the journal Advances in ScienceA team of scientists has determined a new pressure scale, which is important for understanding the formation of the Earth.

Using x-rays from RIKEN’s powerful spectrometer Spring-8 The center avoided some large approximations of previous work, finding that the previous 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 similar to someone running a marathon who thinks it’s 26 miles (42 km), but finds out they’ve only run 21 miles (34 km). While 20% may seem like a modest adjustment, it has major implications.

Effects on Earth Formation

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 is about twice what was previously expected, and in fact the total weight of light material in the entire core is probably five times, or more, that of the Earth’s crust – the living layer in it.

Research Methodology

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 (<0.000000001 grams = 1 nanogram) was placed under intense pressure by crushing it between two diamond crystals in a Diamond Anvil Cell (DAC).

The cell was placed in the large spectrometer of IXS in BL43LXU (figure 2) and small (~1 ppm) changes in the power of x-rays scattered from the rhenium were carefully measured, allowing the researchers to determine the speed of sound of the rhenium. .

They determined both the compression/height and shear/transverse resonance, as well as the abundance of rhenium. That allowed researchers to determine the low pressure of rhenium.

Rhenium Stress as a Stress Indicator

A new study provides a direct relationship between rhenium concentration and depression. Baron says, “The density of rhenium at high pressure is direct and fast 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 this pressure, it is possible only using RIKEN’s spectrometer BL43LXU 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 say: “When we used our new scale to interpret how metal behaves under great pressure and compared it to Earthquake, we found that the light objects hidden in the inner core are probably twice as much as previously expected. Similar changes, perhaps even greater, can be expected when considering the structure of other planets. Our work also suggests a re-examination of the pressure dependence of almost all materials that have been measured at pressures similar to or greater than that of the Earth’s core.

Reference: “Earth’s core density revealed by multimegabar pressure scale” by Daijo Ikuta, Eiji Ohtani, Hiroshi Fukui, Tatsuya Sakamaki, Rolf Heid, Daisuke Ishikawa and Alfred QR Baron, September 8, 2023, Advances in Science.
DOI: 10.1126/sciadv.adh8706