Earth’s inner core may have stopped spinning and may be deteriorating, research suggests
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The rotation of SoilHumans’ inner core may have paused and may even be regressing, new research suggests.
The Earth consists of the crust, the mantle, and the inner and outer cores. The solid the inner core is about 3,200 miles 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 rotation of the Earth itself.
With a radius of nearly 2200 miles, the core of the Earth is about the size of Mars. It consists mainly of iron and nickel and contains about one third of the mass of the Earth.
In research published in the journal Natural Geosciences on Monday, Yi Yang, an associate research scientist at Peking University, and Xiaodong Song, a professor at Peking University, studied seismic waves from earthquakes that have traveled along similar paths through the Earth’s inner core since the 1960s to conclude how fast the inner core is spinning.
What they found was unexpected, they said. Since 2009, seismic records, previously changed over time, showed little difference. This, they said, suggested that the rotation of the inner core had paused.
“We show surprising observations that indicate that the inner core has almost stopped rotating over the past decade and may be undergoing a reversal,” they wrote in the study.
“If you look at the decade between 1980 and 1990, you see clear changes, but if you look at 2010 to 2020, you don’t see much change,” added Song.
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 could shed light on how these layers interact and other processes deep within the Earth.
However, the speed of this rotation and whether it varies is debated, said Hrvoje Tkalcic, a geophysicist at Australian National University, who was not involved in the study.
“The inner core doesn’t come to a complete stop,” 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 catastrophic is happening,” he added.
Song and Yang argue that, based on their calculations, a small electromagnetic and gravitational imbalance could slow or even reverse the rotation of the inner core. They believe this is part of a seven-decade cycle and that the turning point prior to the turning point they found in their data around 2009/2010 was in the early 1970s.
Tkalcic, who is the author of “The Earth’s Inner Core: Revealed by Observational Seismology,” said the study’s “data analysis is sound.” However, the study’s findings should be “taken with caution” as “more data and innovative methods are needed to shed light on this interesting problem.”
Song and Yang agreed that more research was needed.
Tkalcic, who devotes an entire chapter of his book to the rotation of the inner core, suggested that the inner core cycle is every 20 to 30 years, rather than the 70 suggested in the latest study. He explained why such variations occur and why it was so difficult to understand what is happening in the inner reaches of the planet.
“The objects of our studies are buried thousands of miles beneath our feet,” he said.
“We use geophysical inference methods to infer 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 with imperfect or limited equipment. So despite progress, our view of the inner Earth is still hazy and we are still in the discovery phase.”
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