Under the surface of the Earth, a giant may have begun to rotate in the other direction than us, according to a study whose conclusions should not put an end to the controversy that infuriates specialists on the subject.
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This study, published Monday in Nature Geoscience, suggests that Earth’s core, a blazing ball the size of Pluto, has stopped spinning and may have gone the other way.
This “planet within a planet” is made primarily of iron, 5,000 kilometers below the surface, and is free to move, as it floats in the liquid envelope of the outer core.
The exact mechanism for this alternation remains debated. Because what little we know is based on careful analysis of seismic waves, which are caused by earthquakes, when they pass through the center of the planet.
Analyzing seismic wave data over the past 60 years, Xiaodong Song and Yi Yang of Peking University concluded that the core’s rotation “roughly stopped around 2009 before turning back in the opposite direction.”
“We think that, relative to the Earth’s surface, the central core rotates in one direction and then another, like a seesaw,” they told AFP.
“The full cycle (back and forth) of this swing is about seventy years,” they say. The last rotation change before the 2009 change was to occur in the early 1970s, and the next change will occur in the mid-40s, completing the cycle, according to Chinese researchers.
According to them, this rotation will be to some extent related to changes in the length of the day, which are slight differences in the exact time it takes for the Earth to rotate on its axis.
So far, there are few indications of the effect of this rotation on what happens on Earth’s surface. But the authors are convinced that there are physical connections between all the layers that make up the Earth.
“We hope that our research will motivate researchers to design and test models that treat the Earth as an integrated dynamical system,” they explain.
Independent experts welcomed this research with interest, but with some reservations.
“This is a very careful study by excellent scientists who used a lot of data,” John Vidal, a seismologist at the University of Southern California, told AFP. But according to him, “none of the existing models explain all the available data really well.”
Jon Vidal published a study last year indicating that the inner core is swinging faster, changing direction about every six years, according to seismic data from two nuclear explosions dating back to the late 1960s and early 1960s. 1970.
A moment of change close to what the Chinese researchers’ study indicated was a “coincidence,” according to the American seismologist.
Another theory, with a solid foundation according to Mr Vidale: the inner core only moved significantly between 2001 and 2013, before leveling off since then.
For Hrvoje Tkalcic, a geophysicist at the Australian National University, the indoor core cycle is 20 to 30 years, rather than the 70 years suggested by the study in Nature Geoscience.
“Perhaps all of these mathematical models are incorrect,” he says, because even if they explain the observed data, the latter may answer other models that have yet to be imagined.
Therefore, the geophysical community, according to him, has every reason “to be divided over this discovery, and the topic remains controversial.”
He compares seismologists to doctors “who study a patient’s internal organs with imperfect or limited equipment”. As if we are trying to understand the work of the liver only with the help of ultrasound.
Without a scanner equivalent, “our representation of the Earth’s interior remains ambiguous,” he says, anticipating more surprises in the field. Like the theory that the inner core hides a smaller ball of iron inside, similar to Russian dolls.
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