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

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

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

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

Exactly how the inner core rotates 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 pass through the middle of the Earth.

Seeking 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.

Study authors Xiaodong Song and Yi Yang of Peking University in China said they found that inner core rotation “almost stopped around 2009 and then rotated in an opposite direction”.

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

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

Photo by DeAgostini/Getty Images

“A swing cycle lasts about seven decades,” meaning it changes direction about every 35 years, they said.

They said he previously changed direction in the early 1970s and predicted the next flip-flop would be in the mid-2040s.

The researchers said this rotation roughly aligns with changes in what’s called “daylength” – small variations in the exact time it takes Earth to rotate on its axis.

So far, there’s no evidence that what the inner core does has much effect on us surface dwellers.

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

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

“The geophysical community will be divided”

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

“This is a very careful study by excellent scientists who have provided a lot of data,” said John Vidale, a seismologist at the University of Southern California.

“(But) none of the models explains all the data very well in my opinion,” he added.

Vidale published research last year suggesting that the inner core oscillates 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.

This period is around the time Monday’s research indicates that the inner core last changed direction – which Vidale called “kind of a coincidence.”

Another theory – which Vidale says has good supporting evidence – is 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 is every 20 to 30 years, rather than the 70 proposed in the latest study.

“These mathematical models are most likely all incorrect because they explain the observed data but are not required by the data,” Tkalcic said.

“Therefore, the geophysical community will be divided on this discovery and the subject will remain controversial.”

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

Without something like a scanner, “our picture of inner Earth is still blurry,” he said, predicting more surprises to come.

This could include more information on a theory that the inner core could contain another ball of iron inside – like a Russian doll.

“There’s something going on and I think we’re going to figure it out,” Vidale said. “But it may take a decade.”

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