Earth’s inner core may have stopped spinning and may be reversing, study suggests

(CNN) — The rotation of Earth’s inner core may have paused, and possibly even reversed, according to a new study.

The Earth is made up of the crust, mantle, and inner and outer cores. The solid inner core lies about 3,200 miles below the Earth’s crust, separated from the semi-solid mantle by a liquid outer core, which allows the inner core to spin at a different speed than the Earth’s own rotation.

With a core radius of nearly 2,200 miles, Earth is about the size of Mars. It is mainly composed of iron and nickel and accounts for about one-third of the mass of the earth.

In the study published Monday in the journal Nature Geoscience, Peking University associate researcher Yi Yang and Peking University chair professor Song Xiaodong studied core rotation from seismic waves generated by earthquakes following similar paths through the Earth’s core since the 1960s speed.

What they found was unexpected, they said. Since 2009, the previous seismic record over time has barely changed. This, they say, indicates that kernel rotation has paused.

“Our observations are surprising, suggesting that the inner core has nearly stopped spinning in the last decade and may be undergoing an inversion,” they wrote in the study.

“Look back over the decade from 1980 to 1990 and you can see clear changes, but from 2010 to 2020 you don’t see much change,” Song added.

The rotation of the inner core is driven by a magnetic field generated by the outer core and balanced by the gravitational pull of the mantle. Understanding how the inner core rotates can shed light on how these layers interact with each other and other processes deep within the Earth.

However, this rate of rotation, and whether it changes, is controversial, says geophysicist Hrvoje Tkalcic of the Australian National University, who was not involved in the study.

“The kernel didn’t stop completely,” he said. He said the study’s findings “mean that the inner core is now more in sync with the rest of the Earth than it was a decade ago, when it was spinning a bit faster.”

“Nothing catastrophic happened,” he added.

Song and Yang argue that, based on their calculations, a tiny imbalance in the forces of electromagnetism and gravity could slow down or even reverse the rotation of the inner core. They believe this is part of a seven-decadal cycle, with the turning point they detected in the data around 2009/2010 occurring in the early 1970s.

Tkalcic, author of Earth’s Inner Core: What Observational Seismology Reveals, said the study’s “data analysis is solid.” However, the study’s results “should be treated with caution” as “more data and innovative approaches are needed to shed light on this interesting question.”

Song and Yang agree that more research is needed.

study the earth’s core
Tkalcic, who devotes an entire chapter of his book to core rotation, suggests that the core cycle every 20 to 30 years, rather than the 70 years proposed in the latest study. He explains why this change is happening, and why it’s so hard to understand what’s going on in the deepest part of the planet.

“The objects we study are buried thousands of kilometers beneath our feet,” he said.

“We use geophysical reasoning methods to infer the Earth’s interior properties, and caution must be exercised until multidisciplinary findings confirm our hypotheses and conceptual framework,” he explained

“You can think of seismologists as doctors who study the internal organs of a patient’s body using imperfect or limited equipment. So despite the progress, our picture of the Earth’s interior is still hazy, and we’re still in the discovery phase.”

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