Earth's inner core may have started spinning in a different way: Study

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

Deep below the surface, Earth’s inner core may have changed direction, new research suggests.

Far below our feet, a giant may have begun to move against us.


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 in the opposite direction, research suggested Monday.

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

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

What little is known about the inner core comes from measuring small differences 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 Geoscience of nature 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 rotation of the inner core “almost stopped around 2009 and then turned in the opposite direction.”

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

“A swing cycle is about seven decades long,” meaning it changes direction roughly every 35 years, they added.

They said it previously changed direction in the early 1970s and predicted the next change would occur in the mid-2040s.

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

Stuck in the middle

So far, there is little to indicate that what the inner core is doing has much effect on the surface dwellers.

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

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

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

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

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

Vidale published research last year that suggests the inner core oscillates much faster, changing direction every six years or so. 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 “kind of a coincidence.”

Geophysicists “divided”

Another theory — which Vidale said he has some good evidence to support — is that the inner core only moved significantly between 2001 and 2013 and has stayed put 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,” Tkalcic said.

“Therefore, the geophysical community will be divided over 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.”

Absent something like a CT scan, “our picture of the inner Earth is still fuzzy,” he said, predicting more surprises to come.

This could include more on a theory that the inner core might still have an iron ball inside it – like a Russian doll.

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

“But it may take a decade.”

More information:
Yi Yang et al., Multidecadal Variation of Earth’s Inner Core Rotation, Geoscience of nature (2023). DOI: 10.1038/s41561-022-01112-z

© 2023 AFP

Citation: Earth’s inner core may have started spinning the other way: Study (2023, January 24) Retrieved January 24, 2023, from https://phys.org/news/2023-01-earth-core.html

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