Far below our feet, a giant might have begun to move against us.
Earth The inner coreA hot iron ball, the size of Pluto, has stopped spinning in the same direction as the rest of the planet, research suggested Monday, and may be spinning in the other direction.
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 the subtle differences in seismic waves — sometimes generated by earthquakes or nuclear explosions — as they pass through the middle of the Earth.
In an effort to track the movements of the inner heart, new research published in the journal Natural Earth Sciences They analyzed seismic waves from frequent earthquakes over the past six decades.
The study authors, Xiaodong Song and Yi Yang of Peking University of China, said they found that the inner core’s rotation “nearly stopped around 2009 and then shifted in the opposite direction.”
“We think the inner core rotates relative to the Earth’s surface back and forth like a swing,” they told AFP.
They added that “one cycle of the seesaw is about seven decades,” which means it changes direction about every 35 years.
They said it had previously changed direction in the early 1970s, and they expected the next shift to be in the mid-1940s.
The researchers said that this rotation roughly aligns with changes in the so-called “day length” — small differences in the exact time it takes for the Earth to rotate on its axis.
stuck in the middle
So far, there isn’t much to suggest that what the inner core does has much effect on the surface inhabitants.
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 that our study will motivate some researchers to build and test models that treat the whole Earth as an integrated dynamic system,” they said.
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 put in a lot of data,” said John Vidal, a USC seismologist.
“(But) none of the models explain all the data well in my opinion.”
Vidale published research last year indicating that the inner core is swinging at a faster rate, changing direction every six years or so. His work was based on two seismic waves Nuclear explosions In the late 60’s and early 70’s.
That timeframe is getting close to the point where Monday’s research says the inner core last changed direction — which Vidal called “a bit of a coincidence.”
Another theory — which Vidal said has some good evidence to back it up — is that the inner core only moved significantly between 2001 and 2013 and has remained in place since then.
Hrvoje Tkalcic, a geophysicist at the Australian National University, has published research suggesting that the inner core cycle is every 20 to 30 years, instead of 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 topic will remain controversial.”
He likened seismologists to doctors “who study the internal organs of patients’ bodies using imperfect or limited equipment”.
In the absence of something like a CT scan, he said, “our picture of the Earth’s interior is still hazy,” and he expected more surprises to come.
This could include more on the theory that the inner core may have another ball of iron inside it – like a Russian doll.
“Something is going on and I think we’ll find out,” said Vidal.
“But it could take a decade.”
Yi Yang et al., Multidecadal variation of Earth’s internal rotation, Natural Earth Sciences (2023). DOI: 10.1038/s41561-022-01112-z
© 2023 AFP
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