Earth’s solid iron core is not what it seems. In fact, just this year, scientists discovered that our planet’s innermost sphere is textured, not smooth; and every seventy years it stops rotating before changing direction. Now, in another surprising study, a team of researchers believes they have figured out why Earth’s hard iron core is slightly softer than expected: Its atoms can move.

In the Earth’s inner core, about 5,100 kilometers (or 3,170 miles) below our feet, iron atoms are tightly packed into a hexagonal structure compressed under tremendous pressure and high temperatures. Recent seismic observations have shown that the Earth’s inner sphere exhibits some intriguing properties, being more similar to soft metals like lead and closer to molten iron than the solid bulk we imagine in our minds.

This is because the iron atoms in the inner core shift position within their proposed hexagonal lattice, according to physicist Yujun Zhang of Sichuan University in China and colleagues in the US and China, who conducted a series of computer simulations and laboratory experiments. structure.

Zhang and his colleagues suggest that, just as people change seats at the dinner table, iron atoms migrate to neighboring positions without disrupting the basic metallic structure of iron, making the nucleus more flexible.

“Solid iron becomes surprisingly soft deep within the Earth because its atoms can move much further than we imagined,” Zhang explains. “This increased movement makes the inner core less rigid, more vulnerable to shear forces.”

Before that, scientists modeled the Earth’s inner core using computer models that tended to capture less than a hundred atoms arranged in a repeating hexagonal structure. Some researchers have also suggested that pockets of melt in the Earth’s inner core could explain some of the observed features. But Zhang and his colleagues suggest that these pockets probably compressed as the core solidified, and that no theory has yet been able to comprehensively explain the strange elasticity of Earth’s inner sphere.

To expand their insight into lattice dynamics, Zhang and his colleagues used a supercomputer and a machine learning algorithm to simulate a much larger atomic environment containing more than 10,000 atoms. The researchers used model data collected during high-pressure and high-temperature laboratory experiments designed to simulate conditions in the Earth’s inner core.

At pressures in the range of 230 to 330 GPa and temperatures slightly below the melting point of iron, simulations of the densely packed lattice structure show that the iron atoms move according to a collective motion scheme; “when an atom pops out of its equilibrium position and repels neighboring atoms.” .

This rapid propagation occurs in picoseconds, a trillionth of a second, so that movement does not disrupt the lattice structure. Instead, the atoms shake, causing the iron core to behave like an extremely soft solid.

These results are, of course, based on theoretical calculations of a substance that scientists cannot sample and whose properties they can only predict from afar. Despite these limitations, the results are in good agreement with seismic observations.

“We now know a fundamental mechanism that will help us understand the dynamic processes and evolution of the Earth’s inner core,” said senior author Jung-Fu Lin, a geoscientist at the University of Texas at Austin. Source