Earth’s inner core appears to be slowing down


In the mid-1990s, scientists found evidence that Earth’s inner core, a ball of superheated iron slightly smaller than the Moon, was spinning at its own speed, only slightly faster than the rest of the planet. A study now published in Nature Geoscience shows that around 2009, The core slowed down its spin to spin in sync with the surface for a while — now lagging behind it.

The provocative findings come after years of research and deep scientific disagreement about some of the most fundamental aspects of Earth’s core and how it affects our planet, including the length of the day and fluctuations in Earth’s magnetic field.

Three thousand miles below the surface, a glowing ball of solid iron floats within a liquid outer core. Geologists believe that energy released in the inner core causes fluid in the outer core to move, creating electrical currents that in turn create a magnetic field that surrounds the Earth. This magnetic shield protects life on the surface from the most damaging forms of cosmic radiation.

Don’t panic. The slowdown of the core is not the beginning of the end.The same thing seemed to happen in the late 1960s and early 1970s, with study authors at Peking University in China It is suggested that it may represent a 70-year cycle of acceleration and deceleration of the core’s spin.

But while other experts have praised the rigor of the analysis, the research will intensify rather than resolve a bitter scientific debate about the mysterious metallic sphere at the center of the Earth.

“It’s just moot because we can’t figure it out,” said John Vidale, a geophysicist at the University of Southern California. “It could be benign, but we don’t want something deep in the Earth that we don’t understand.”

The new study was led by Peking University geoscientist Song Xiaodong, whose work in 1996 provided the first evidence that Earth’s core is doing its own thing. Buried beneath the mantle and crust, Earth’s core is too deep to observe directly, but scientists can use seismic waves from earthquakes to infer what’s going on inside the planet. Seismic waves travel at different speeds depending on the density and temperature of the rock, so they act like a kind of X-ray to Earth.

The study examined seismic waves propagating from the earthquake site to sensors on the back of the Earth, passing through the core on the way. By comparing earthquake-like waves that hit the same location over the years, scientists are able to search for and analyze time lags and disturbances in the waves that provide them with indirect information about the Earth’s core — or, as some scientists call it, the Earth’s core. The inner planets of our planet.

“The inner core is the deepest layer of the Earth, and its relative rotation is one of the most interesting and challenging questions in deep Earth science,” Song said in an email.

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The core behavior may be related to small changes in the length of the day, although the details are debated. The length of the day has been increasing by milliseconds for centuries due to other forces, including the moon’s gravitational pull on Earth. But ultra-precise atomic clocks measured mysterious fluctuations.

Song and colleagues suggest that these changes may coincide with changes in core rotation. The new paper found that when they removed the predictable fluctuations in day length due to lunar tidal forces, there were variations that appeared to coincide with the 70-year oscillation of the inner core’s rotation.

Seismologist Paul Richards Columbia University’s Lamont-Doherty Earth Observatory, in collaboration with Song, presents preliminary evidence that the core rotates faster than other parts planet.

“Most of us assume that the inner core spins at a slightly different steady speed than Earth’s,” Richards said. “The evidence is accumulating, and this paper shows that the evidence [faster] The rotation was strong around 2009 and basically died in the following years. “

Still, he cautions that things can quickly become speculative when trying to understand the impact of the geonuclear nucleus on other phenomena. This is because the behavior of the core itself is still a matter of debate – simple assumptions have been refined over the years.

For example, there is evidence to support other ideas about how the Earth’s core works. Vidale of the University of Southern California, who has studied seismic waves from nuclear explosions, favors a shorter six-year oscillation period for the rotational velocity of the Earth’s core.

Stony Brook University seismologist Lianxing Wen completely rejects the idea that the Earth’s core spins independently. He believes that changes in the inner core’s surface over time are a more plausible explanation for the seismic data.

“This study misinterpreted seismic signals caused by sporadic changes in the surface of the Earth’s inner core,” Wen said in an email. He added that the idea that the inner core rotates independently of the surface “provides inconsistent interpretations of the seismic data, even if we assume it to be true.”

What geoscientists agree on is that many of the original ideas about the core behavior became more complex as more and more data accumulated.

“At the end of the day, I don’t think it’s a problem in geoscience that things get complicated,” Elizabeth Day, a geophysicist at Imperial College London, said in an email. “We know that the surface of our planet is complex… so it’s reasonable to assume that the deep interior is also complex! To definitively show how the inner core rotates relative to Earth’s outer layers, we need to continue collecting as much data as possible.”

The stakes are high in this scientific debate, in part because at its core is a latent, unsolved mystery so close to home.

“It’s not going to affect the price of potatoes tomorrow,” Richards said. But the debate touches on deeper questions, such as how Earth’s formation and its inner layers supported life on its surface, which could help research into the habitability of rocky planets orbiting other stars.

“When you think about … what our planet is made of and what its history is,” Richards said, “a deep understanding of the inner core gets you into ‘how did all these divisions of the Earth evolve ?'”

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