A giant may have begun to move against us, well below our feet.
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 the other way, according to a study Monday.
About 5,000 kilometers (3,100 miles) below the surface we live on, this “planet within a planet” can spin independently as the liquid metal floats in the outer core.
How exactly the inner core rotates has been a topic of debate among scientists, and recent research is expected to be controversial.
What little is known 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.
The new research, published in the journal Nature Geoscience and looking to track the movements of the inner core, analyzed seismic waves from earthquakes that have recurred over the past sixty years.
The study’s authors, Xiaodong Song and Yi Yang of Peking University in China, said they found that the rotation of the inner core “nearly came to a halt around 2009 and then reversed.”
“We believe the inner core rotates back and forth like a swing relative to the Earth’s surface,” they told AFP.
“One cycle of oscillation is about seventy years,” they added, meaning it changes direction roughly every 35 years.
They previously said it changed direction in the early 1970s and predicted the next turn would be in the mid-2040s.
This rotation is roughly in line with changes in what’s called the “length of the day,” the researchers said — tiny differences in the time it takes for the Earth to spin around its axis.
– Stuck in the middle –
So far, there has been little to suggest that what the inner core does has much of an 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 our work will motivate some researchers to build and test models that treat the entire Earth as an integrated dynamical system,” they said.
Experts not involved in the study expressed caution about their 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 out a lot of data,” said John Vidale, a seismologist at the University of Southern California.
“(But) none of the models, in my opinion, explains all the data very well,” he added.
Vidale published research last year that suggested the inner core oscillates much faster and changes direction 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 — what Vidale calls “a kind of coincidence.”
– Geophysicists ‘divided’ –
Another theory that has some good evidence to support it is that the inner core only moved significantly between 2001 and 2013 and has remained where it has been ever since, Vidale said.
Hrvoje Tkalcic, a geophysicist at the Australian National University, has published research suggesting that the cycle of the inner core occurs every 20 to 30 years, rather than every 70 years suggested in the last study.
“All of these mathematical models are likely wrong because they explain the observed data, but are not essential for the data,” Tkalcic said. said.
“Therefore, the geophysical community will be divided over this finding, and the issue will remain controversial.”
He compared seismologists to doctors who “examined the internal organs of patients’ bodies using defective or limited equipment.”
“Our view of the Earth’s interior is still blurry,” he said, as it’s nothing like a CT scan, and predicted more surprises ahead.
This could include more about a theory that there might be another iron ball inside the inner core – like a Russian doll.
“Something’s going on and I think we’ll figure it out,” Vidale said.
“But it could take ten years.”