New research suggests that the rotation of Earth’s inner core may be suspended and even reversed. (Siktem Simsek, Alamy)
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ATLANTA – New research suggests that the rotation of Earth’s inner core may be suspended and even reversed.
Earth is made up of the crust, mantle, and inner and outer cores. The solid inner core is located about 3,200 miles below the Earth’s crust and is separated from the semi-solid crust by the liquid outer core, which allows the inner core to rotate at a speed different from Earth’s rotation.
Earth’s core is about the size of Mars, with a radius of about 2,200 miles. It consists mostly of iron and nickel, and makes up about one-third of Earth’s mass.
In research published Monday in the journal Nature Geoscience, Peking University associate research scientist Yi Yang and Peking University professor Xiaotong Chang analyzed seismic waves from earthquakes that have passed through Earth’s inner core on similar paths since the 1960s. To estimate how fast the inner core is spinning.
What they found was unexpected, they said. Seismic records since 2009, which have changed over time, have shown little difference. This indicated that the inner core rotation was suspended.
“We show surprising observations that indicate that the inner core has almost stopped its rotation in the last decade and may be experiencing a reversal,” they wrote in the study.
“When you look at the decade between 1980 and 1990 you see a clear change, but when you look from 2010 to 2020 you don’t see much change,” Song added.
The spin 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 can shed light on how these layers interact and other processes deep in the Earth.
However, the speed of this cycle and whether it is changing is debatable, said Hrvoje Tkalcic, a geophysicist at the Australian National University who was not involved in the study.
“The inner core hasn’t come to a full stop,” he said. The study’s finding “is 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 slightly faster,” he said.
“Nothing catastrophic happened,” he added.
Based on their calculations, Chang and Yang argue that a small imbalance in the electromagnetic and gravitational forces can slow down and reverse the rotation of the inner core. They believe this is part of a seven-decade cycle, and that the turning point before the one they found in 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 good.” However, the study’s findings “should be taken with caution” because “more data and innovative methods are needed to shed light on this interesting problem.”
Chang and Yang agree that more research is needed.
Exploring the Earth’s Core
Tkalcic, who devoted an entire chapter of his book to inner core rotation, suggested that the inner core rotates every 20 to 30 years, rather than the 70 proposed in a recent study. He explained why such variations occur and why it was so difficult to understand what was happening in the interior of the planet.
“The objects of our studies are buried thousands of kilometers beneath our feet,” he said.
“We use geophysical inference methods to infer the Earth’s internal properties, and caution should be exercised until more disciplinary findings confirm our hypotheses and conceptual frameworks,” he explained.
“You can think of seismologists like medical doctors studying the internal organs of patients’ bodies using imperfect or limited equipment. So, despite progress, our picture of the inner Earth is still blurry, and we’re still in the discovery phase.”