A new study finds that the rotation of the Earth’s inner core has slowed, causing the planet’s core to rotate in a slightly slower clip than the upper layers. Deceleration not only changes the rotation speed of the planet as a whole, but it can affect how the core evolves over time.
About new research published in the journal natural earth sciences, Scientists have used a database of earthquakes to study the behavior of the Earth’s solid inner core over time. The inner core is suspended like a ball he bearing in the molten metal sea of the outer core. Because of this liquid cocoon, the “ball bearing” may not rotate at the same speed as the rest of the Earth. Over the years, some researchers have found that the core rotates slightly faster than the mantle and crust. This is a state called “super rotation”. However, studies have not returned consistent figures. The first study to observe differential rotation of the core estimated that the inner core is rotating up to 1 degree faster than the rest of the Earth per year. Others have found an annual speedup of a small percentage of 1 degree.
These differences are not dramatic. The variation in rotation time between the inner core and the rest of the Earth is very small.The difference isn’t even ostensibly life-threatening: in contrast to his 2003 sci-fi movie core, You don’t need to call in a crack team of geophysicists and astronauts to drill down to the core of the earth and start blasting. At best, the rotation of the inner core influences the Earth’s global spin and may contribute to fluctuations in the planet’s magnetic field. Seismic studies show that the core expands by about a millimeter each year, solidifying some of the molten iron in the outer core. Coagulation also promotes circulation in the outer core, which in turn creates the planet’s magnetic field. The rotation of the inner core influences this solidification process in ways that are not yet fully understood, and could influence the magnetic field, said Xiaodong Song, study author and geophysicist at Peking University in China. said.
Rotation could also affect how the inner core grows over billions of years, said a geophysicist at the University of Southern California, who was not involved in the study, but who was not involved in the study. John Vidale, who studies the rotation of
The problem, however, is that no one really knows how fast the inner core rotates. In a new study, Yi Yang, a geophysicist at Peking University who also works with Song, found that from the 1970s to his early 2000s, the core appeared to maintain a steady rotation faster than the rotation of the entire Earth. Did. Around 2009, however, its rotation slowed sharply to match Earth’s speed, and then probably slowed significantly, causing the rest of the planet to spin faster.
Song and Yang measured this spin using a pair of near-identical earthquakes that occurred at the same location, separated only by time. Since earthquakes are about the same, shock waves should look the same as they travel through the core and back. That is, unless the core itself changes and changes the wave path of one quake, it will be detected by seismometers around the Earth. compared to others. If the core rotates differently than the rest of the Earth, identical seismic waves occurring months or years apart will hit the core at slightly different locations and thus bounce off with some subtle differences. Researchers compared seismic waves dating back to 1964 to track changes in core motion over time. If they are correct, the rotation of the core will lag slightly behind the rotation of the planet as a whole.
“We believe that this [slowed rotation] It will continue for years and decades to come. [our] It’s a relatively short human time frame,” Song says.
The new findings probably don’t end the debate on the inner core. But there are several competing explanations for what is happening. For example, Vidale’s study suggests that the core may change its rotation about every 6 years, while researchers Guanning Pang and Keith Koper suggested in the early 2000s that a single “tilt ”, and that little has changed since the 2022 study. “Do not look [the new work] It’s absolutely definitive,” says Vidale.
Lianxing Wen, a geodynamic scientist at Stony Brook University, is also studying core spins, although he wasn’t involved in the new work. He does not believe that the rotation of the inner core differs from the rest of the Earth. A better explanation for the variation of seismic waves passing through the core, says Wen, is that the surface of the inner core is uneven and constantly changing, not as smooth as a ball bearing. “We believe that the inner core has a changing topography that best explains the observed temporal variations in the seismic waves reflecting off the inner core,” he says. Weng says the new research mistakenly believes these changes are caused by the core’s spin rather than by the fluctuating surface.
Fortunately, Earth’s seismic monitoring has never been better, providing much richer data on the Earth’s interior than in previous decades. By continuing to observe seismic waves, researchers should be able to show whether the rotation of the inner core is correct.
“The exciting news is that we don’t have to wait too long,” Song says.
