Earth’s inner core may have started spinning the other way, study says

Earth’s inner core, a hot iron ball the size of Pluto, has stopped spinning in the same direction as the rest of the planet and may even be spinning in the opposite direction, research suggested Monday.

About 3,100 miles below Earth’s surface, this “planet within a planet” can rotate independently because it floats in the liquid metal outer core.

Exactly how the inner core spins has been the subject of debate among scientists – and the latest research is expected to prove controversial.

What little we know about the inner core comes from measuring the tiny differences in seismic waves — created by earthquakes or sometimes nuclear explosions — as they traverse the center of the Earth.

To track the movements of the inner core, new research published in the journal Nature Geoscience analyzed seismic waves from repeated earthquakes over the past six decades.

The study’s authors, Xiaodong Song and Yi Yang of Peking University in China, said they found that the inner core’s rotation “almost stopped around 2009 and then rotated in the opposite direction.”

“We think the inner core is spinning back and forth relative to the Earth’s surface, like a seesaw,” they told AFP.

Diagram of the Earth's interior showing the crust
Diagram of the Earth’s interior showing the crust (aluminium, silicate), mantle (magnesium, silicate) and core (iron, nickel). color illustration.

Photo by DeAgostini/Getty Images

“One cycle of the swing takes about seven decades,” meaning it changes direction about every 35 years, they said.

They said it had already changed direction in the early 1970s and predicted the next reversal would occur in the mid-2040s.

The researchers said this rotation roughly coincides with changes in what’s known as “daylength” — small variations in the exact time it takes for the Earth to spin around its axis.

So far, little suggests that what the inner core does has much impact on us surface dwellers.

But the researchers said they believe there are physical connections between all layers of the Earth, from the inner core to the surface.

“We hope that our study can motivate some researchers to build and test models that treat the entire Earth as one integrated dynamical system,” they said.

“The geophysical community is being divided”

Experts not involved in the study have expressed caution about their findings, citing several other theories and warning that many mysteries about the center of the Earth remain.

“This is a very thorough study by excellent scientists, and it’s a lot of data,” said John Vidale, a seismologist at the University of Southern California.

“(But) neither model explains all the data very well, in my opinion,” he added.

Vidale published a study last year that suggests the inner core vibrates much faster, changing direction about every six years. His work was based on seismic waves from two nuclear explosions in the late 1960s and early 1970s.

That time frame is around the point where Monday’s research says the inner core last changed direction — which Vidale called “some kind of coincidence.”

Another theory — which Vidale says has some good evidence to back it up — suggests that the inner core only moved significantly between 2001 and 2013 and has remained in place ever since.

Hrvoje Tkalcic, a geophysicist at the Australian National University, has published research suggesting that the inner core cycle occurs every 20 to 30 years instead of the 70 years suggested in the latest study.

“These mathematical models are most likely all wrong because they explain the observed data but are not necessary for the data,” Tkalcic said.

“As such, the geophysical community will be divided over this finding and the topic will remain controversial.”

He compared seismologists to doctors “who examine the internal organs of patients’ bodies with imperfect or limited equipment”.

In the absence of anything like a CT scan, “our picture of inner Earth is still blurry,” he said, predicting more surprises.

This could include more about a theory that the inner core could contain yet another iron ball – like a Russian doll.

“Something’s happening and I think we’re going to find out,” Vidale said. “But it may take a decade.” Earth’s inner core may have started spinning the other way, study says

Rick Schindler

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