The Earth’s inner core may have started spinning in a different way: research

Far below our feet, a giant might move against us.

Earth’s inner core, a hot iron orb the size of Pluto, has stopped spinning in the same direction as the rest of the planet and may even spin the other way, research on Monday suggests.

About 5,000 kilometers (3,100 miles) below the surface where we live, this “planet within a planet” can spin independently because it floats in a liquid metal outer core.

Exactly how the inner core spins has been debated among scientists – and the latest research is set to prove controversial.

What little is known about the inner core comes from measuring tiny variations in seismic waves – created by earthquakes or sometimes nuclear explosions – as they pass through the center 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.

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

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

“One fluctuation cycle lasts about seven decades,” meaning it changes direction roughly every 35 years, they added.

They said it previously changed direction in the early 1970s and predicted the next turn would be in the mid-1940s.

The researchers found that this rotation roughly coincides with changes in the so-called “day length” – slight variations in the exact amount of time it takes the Earth to rotate on its axis.

– Stuck inside –

So far, there is little indication that what the inner core does has a big impact on surface dwellers.

But the scientists 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 will motivate some researchers to build and test models that treat the entire Earth as an integrated dynamic system,” they said.

Experts uninvolved in the study expressed caution about its results, pointing to several other theories and warning that many mysteries remain around the center of the Earth.

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

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

Vidale published research last year suggesting that the inner core oscillates much faster, changing direction roughly every six years. His work was based on seismic waves from two nuclear explosions in the late 1960s and early 1970s.

This time frame is close to the point where Monday’s surveys indicate that the inner core recently changed direction – what Vidale called “a kind of coincidence.”

– Geophysicists “divided” –

Another theory – which Vidale says has good evidence to support it – 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 occurs 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,” said Tkalcic.

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

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

Missing something like a CT scan, “our picture of the inner Earth is still fuzzy,” he said, anticipating more surprises.

This may include more information on the theory that the inner core may have another iron ball inside it – like a Russian doll.

“Something’s going on and I think we’re going to sort it out,” Vidale said.

But that could take a decade.

dl/gil

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