Earth’s core has stopped spinning and may invert, study suggests

The rotation of Earth’s inner core may have stopped and may even be spinning in reverse, new research suggests.

The Earth is made up of the crust, the mantle, and the inner and outer cores. The solid inner core is situated about 5,100 kilometers below the Earth’s crust and is separated from the semi-solid mantle by the liquid outer core, which allows the inner core to rotate at a different speed than the Earth itself.

With a radius of nearly 3,500 kilometers, the Earth’s core is about the size of Mars. It consists mainly of iron and nickel and contains about a third of Earth’s mass.

In search published in the journal Nature Geoscience on Monday (23), Yi Yang, a scientist at Peking University, and Xiaodong Song, a professor at Peking University, studied seismic waves from earthquakes that passed through the Earth’s inner core along similar paths. from the 1960s to inferring how fast the inner core is spinning.

The findings were unexpected, they said. Since 2009, seismic records, which previously changed over time, have shown little difference. This, they said, suggested that the inner core’s rotation had stopped.

“We show surprising observations that indicate that the inner core has almost ceased its rotation in the last decade and may be experiencing a retrogression,” they wrote in the study.

“When you look at the decade between the 1980s and 1990s you see a clear shift, but when you look from 2010 to 2020 you don’t see much change,” added Song.

The rotation of the inner core is driven by the magnetic field generated in the outer core and balanced by the gravitational effects of the mantle. Knowing how the inner core rotates could shed light on how these layers interact and other processes deep within the Earth.

However, the speed of that rotation, and whether it varies, is debated, said Hrvoje Tkalcic, a geophysicist at the Australian National University who was not involved in the study.

“The inner core doesn’t stop completely,” he said. The study’s finding, he said, “means that the inner core is now more in sync with the rest of the planet than it was a decade ago, when it was spinning a bit faster.”

“Nothing cataclysmic is happening,” he added.

Song and Yang argue that, based on their calculations, a small imbalance in the electromagnetic and gravitational forces could slow and even reverse the rotation of the inner core. They believe this is part of a seven-decade cycle, and that the turn before the one they detected in their data around 2009/2010 occurred in the early 1970s.

Tkalcic, author of “The Earth’s Inner Core: Revealed by Observational Seismology,” said the study’s “data analysis is solid.” However, the study’s findings “should be viewed with caution” as “more data and innovative methods are needed to shed light on this interesting problem.”

Song and Yang agreed that more research is needed.

Studying the Earth’s core

Tkalcic, who devotes an entire chapter of his book to inner core rotation, suggested that the inner core cycles every 20 to 30 years, rather than the 70 years proposed in the most recent study. He explained why such variations occur and why it is so difficult to understand what happens inside the planet.

“The objects of our studies are buried thousands of kilometers under our feet,” he said.

“We use geophysical inference methods to estimate the Earth’s internal properties, and caution should be exercised until multidisciplinary findings confirm our hypotheses and conceptual frameworks,” he explained.

“You can think of seismologists as doctors who study the internal organs of patients’ bodies using imperfect or limited equipment. So despite progress, our picture of the Earth’s interior is still blurry and we are still in the discovery stage.”