Earth’s inner core seems to be slowing its spin



In the mid-1990s, scientists found evidence that Earth’s inner core, an overheated iron ball slightly smaller than the moon, was spinning at its own pace, just slightly faster than the rest of the planet. Now a study published in Nature Geoscience suggests that around 2009 the core slowed its rotation to swirl in sync with the surface for a while – and is now lagging behind.

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

Three thousand miles below the surface, a red-hot ball of solid iron floats in a liquid outer core. Geologists believe that the energy released by the inner core causes the fluid in the outer core to move, generating electrical currents that in turn create a magnetic field around the planet. This magnetic shield protects surface organisms from the most harmful cosmic rays.

Do not panic. The slowing down of the core is not the beginning of the end times. The same seems to have happened in the late 1960s and early 1970s, and the study’s authors at Peking University in China suggest it may represent a 70-year cycle of the core’s spin speeding up and slowing down.

But while other experts praised the rigor of the analysis, the study will sharpen, not settle, the fierce scientific debate about what the mysterious metal sphere at the center of the Earth is up to.

“It’s only controversial because we can’t figure it out,” said John Vidale, a geophysicist at the University of Southern California. “It’s probably benign, but we don’t want to have things that we don’t understand deep down in the earth.”

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

The study examined seismic waves that traveled from earthquake sites to sensors on the far side of the planet, passing through the core as they went. By comparing waves of similar earthquakes that hit the same spot over the years, the scientists were able to find and analyze time delays and perturbations in the waves that gave them indirect information about the core — or as some scientists call it, the planet within. our planet.

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

Scientists are slowly unraveling the secrets of the Earth’s mysterious hum

The behavior of the core can be linked to minute changes in the length of a day, though the exact details are a matter of debate. The length of a day has increased by milliseconds over centuries because of other forces, including the moon’s gravitational pull on the Earth. But ultra-precise atomic clocks have measured mysterious fluctuations.

These variations may correspond to changes in core rotation, Song and colleagues argue. The new paper finds that, when they remove predictable fluctuations in the length of a day due to the moon’s tidal forces, there are changes that appear to follow with the 70-year oscillations in the rotation of the inner core.

Paul Richards, a seismologist at the Lamont-Doherty Earth Observatory at Columbia University, collaborated with Song to bring forward the first evidence that the core was spinning faster than the rest of the planet.

“Most of us assumed that the inner core rotated at a constant speed that was slightly different from Earth,” Richards said. “The evidence is piling up, and this document shows the evidence for that [faster] rotation is strong before about 2009, and in fact dies down in subsequent years.

Still, he cautioned that things quickly become speculative when you try to understand the core’s influence on other phenomena. That’s because the behavior of the core itself is still a contentious question — with simplistic assumptions becoming increasingly sophisticated over the years.

For example, there are lines of evidence that support other ideas about how the Earth’s core behaves. USC’s Vidale has studied seismic waves generated by nuclear explosions, and he favors a shorter, six-year oscillation for the core’s rotational velocity.

Lianxing Wen, a seismologist at Stony Brook University, completely rejects the idea that the core rotates independently. He argues that changes over time at the surface of the inner core are a more plausible explanation for the seismic data.

“This study misinterprets the seismic signals caused by episodic changes of the Earth’s inner core surface,” Wen said in an email. He added that the idea that the inner core rotates independently of the surface “provides an inconsistent explanation for the seismic data, even assuming it to be true.”

What geoscientists do agree on is that as more data has been collected, many of the original ideas about the core’s behavior have become more complicated.

“Ultimately, I don’t think being complicated is a problem in geoscience,” Elizabeth Day, a geophysicist at Imperial College London, said in an email. “We know that the surface of our planet is complex…so it is reasonable to assume that the deep interior is also complicated! To say with certainty how the inner core rotates in relation to the outer layers of the planet, we will have to continue to collect as much data as possible.’

The stakes of this scholarly debate are high, in part because at its heart is a mystery lurking, unsolved, so tantalizingly close to home.

“This is not something that will affect the price of potatoes tomorrow,” Richards said. But the debate speaks to more profound questions about Earth’s formation and how its inner layers support life on its surface, something that could help explore habitability on rocky planets orbiting other stars.

“When you think… what our planet is made of and what its history is,” Richards said, “a deep understanding of the inner core puts you in ‘How did all these parts of planet Earth evolve?'”

The Valley Voice
The Valley Voice
Christopher Brito is a social media producer and trending writer for The Valley Voice, with a focus on sports and stories related to race and culture.


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