In the mid-1990s, scientists discovered evidence that the Earth’s inner core, a superheated iron ball slightly smaller than the Moon, is spinning at its own pace, slightly faster than the rest of the Earth. bottom. A study published in Nature Geoscience now states that around 2009, The core has slowed its rotation to rotate in sync with the surface for a while, but now lags behind it.

The provocative discovery is the result of years of research and deep understanding of the core and how it affects some of the most fundamental aspects of the Earth, such as the length of the day and variations in the Earth’s magnetic field. Brought after scientific disagreement.

Within a liquid outer core, 3,000 miles below the Earth’s surface, a ball of blazing solid iron floats. Geologists believe that the energy released from the inner core moves the liquid in the outer core, generating electrical currents, which create the magnetic field surrounding the planet. This magnetic shield protects surface life from the most harmful cosmic radiation.

Do not panic. A slowing core is not the beginning of the end.The same appears to have happened in his late 1960s and early 1970s, with study authors from Peking University in China This suggests that it may represent a 70-year cycle of acceleration and deceleration of core spin.

But while other experts have praised the rigor of the analysis, the study isn’t about settling a heated scientific debate about what the mysterious metal ball at the center of the Earth is supposed to be. , would make it sharper.

“It’s controversial because we don’t understand it,” says John Vidale, a geophysicist at the University of Southern California. “Probably benign, but I don’t want to put something deep in the earth that I don’t understand.”

The new study, led by Xiaodong Song, an earth scientist at Peking University, was the first to provide evidence that the core is doing its own thing in a 1996 study. The core, buried beneath the mantle and crust, is too deep to be visualized directly, but scientists can use the seismic waves produced by earthquakes to infer what is happening inside the planet. Seismic waves act as a kind of his X-rays for the Earth, as they travel at different speeds depending on the density and temperature of rocks.

The study looked at seismic waves traveling from the site of an earthquake to sensors on the other side of the globe, passing through the core on the way. By comparing waves from similar earthquakes that hit the same location over the years, scientists can search for and analyze wave lags and perturbations, providing indirect information about the core. I was. our star.

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

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

Core behavior may be related to small changes in day length, but the exact details are debatable. The length of the day has increased by milliseconds over the centuries due to other forces such as the moon’s pull on the earth. However, ultra-precision atomic clocks have measured mysterious fluctuations.

These changes could be consistent with changes in core rotation, Song and colleagues argue. and found that there are variations that appear to follow the 70-year oscillations of the inner core’s rotation.

Seismologist Paul Richards Columbia University’s Lamont-Doherty Earth Observatory, in collaboration with Song, has provided the first evidence that the core is spinning faster than the rest of it. planet.

“Most of us assumed that the inner core was rotating at a slightly different and stable speed than the Earth,” Richards said. “The evidence is accumulating and this paper [faster] Rotation is strong until around 2009, after which it basically tapers off. “

Still, he warned that things would quickly turn into speculation when trying to understand the effects of the core on other phenomena. The simplistic assumptions have become increasingly sophisticated over the years.

For example, there is a body of evidence that supports other ideas about how the Earth’s core behaves. Vidale at USC has studied seismic waves produced by nuclear explosions, and for the core’s rotational velocity he favors shorter six-year oscillations.

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

“This study misinterprets seismic signals caused by transient 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 an inconsistent explanation for the seismic data, even if we assume it to be true.”

What geoscientists agree is that as more data accumulates, many of the early ideas about core behavior are becoming more complex.

Elizabeth Day, a geophysicist at Imperial College London, said in an email: “We know that the surface of the Earth is complex … so it is reasonable to assume that the deep interior is also complex! How the inner core rotates relative to the outer layers of the planet We need to continue to collect as much data as possible in order to articulate the

One of the reasons this scientific debate is so important is that the underlying unsolved mysteries are so intriguingly close at hand.

“This is not going to affect potato prices tomorrow,” Richards said. But this argument raises deeper questions about how the Earth formed and how its inner layers support life on its surface. This could help study habitability on rocky planets orbiting other stars.

“Given what our planet is made up of and what its history is, a deep understanding of the inner core tells us, ‘How did all these splits of planet Earth evolve? said Richards.

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