Perhaps the Earth’s inner core is changing its rotation, scientists say


Such a turn may seem strange, but it is unlikely to have a profound effect on life.

Earth’s inner core may have temporarily stopped rotating relative to the mantle and surface, researchers report in Nature Geoscience journal from January 23. The inner core’s spin direction may now reverse — part of a roughly 70-year cycle that could affect the length of Earth’s days and its magnetic field — though some researchers are skeptical.

“We see compelling evidence that the inner core rotated faster than the surface, [але] until about 2009 it almost stopped,” says geophysicist Xiaodong Song of Peking University in Beijing. “Now it is gradually moving in the opposite direction.”

Such a drastic turn may seem strange, but the Earth is unstable. Break through the ever-changing crust and you’ll find yourself in the titanic mantle, where giant masses of rock have flowed viscously for millions of years, sometimes rising to break the crust’s surface. Delve deeper and you’ll reach Earth’s liquid outer core. Here, circulating flows of molten metals create the magnetic field of our planet. And in the center of that melt, you’ll find a solid, rotating ball of metal about 70 percent as wide as the moon.

It inner core . Studies have shown that this solid core can rotate in the liquid outer core under the influence of the outer core’s magnetic moment. The researchers also say that the mantle’s immense gravitational pull can slow down the rotation of the inner core, causing it to oscillate.

The evidence of fluctuating rotation of the inner core first appeared in 1996 . Geophysicist Paul Richards of Columbia University’s Lamont-Dougherty Earth Observatory in Palisades, N.Y., and Song, who was also at Lamont-Dougherty at the time, reported that over three decades, seismic waves from earthquakes took varying amounts of time to travel through the solid core Earth

The researchers concluded that the inner core rotates at a different rate than the mantle and crust, which accounts for the time difference. The planet rotates approximately 360 degrees per day. Based on their calculations, the researchers estimated that the inner core rotates on average about 1 degree per year faster than the rest of the Earth.

But other researchers have questioned this conclusion, suggesting that the core rotates more slowly than Song and Richards estimate, or doesn’t rotate at all.

In the new study, while analyzing global seismic data dating back to the 1990s, Song and geophysicist Yi Yang, also of Peking University, made a surprising observation.

Until 2009, seismic waves generated by sequences and pairs of repeating earthquakes — known as multiplets and doublets — traveled through the inner core at different speeds. This indicates that waves from repeated earthquakes cross different parts of the inner core, and that the inner core rotates at a different rate than the rest of the Earth, which is consistent with Song’s previous research.

But around 2009, the travel time difference disappeared. This suggests that the inner core has stopped rotating relative to the mantle and crust, Yang says. After 2009, these differences returned, but the researchers concluded that the waves were crossing parts of the inner core, indicating that it was now spinning in the opposite direction relative to the rest of Earth.

The researchers then studied records of earthquake doublets in Alaska dating back to 1964. While the inner core appeared to rotate steadily for most of that time, it appears to have changed rotation again in the early 1970s, the researchers said.

Song and Yang concluded that the inner core may oscillate with a periodicity of about 70 years, changing directions about every 35 years. Because the inner core is gravitationally bound to the mantle and magnetically bound to the outer core, researchers say these fluctuations could explain the known 60-70-year fluctuations in the length of Earth’s days and the behavior of the planet’s magnetic field. However, more work is needed to determine which mechanisms may be responsible.

But not all researchers participate. Yang and Song “identified this last 10-year period, [який] had less activity than before, and I think that’s probably valid,” says geophysicist John Vidale of the University of Southern California in Los Angeles, who was not involved in the study. research. But beyond that, Vidale says, everything becomes controversial.

In 2022, he and his colleague reported that seismic waves from nuclear tests show that the inner core can change its rotation about every three years. Meanwhile, other researchers have suggested that the inner core does not move at all. Instead, they say, changes in the shape of the inner surface of the nucleus can explain the difference in the time of passage of waves.

Future observations will likely help unravel the discrepancies between these studies, Vidale says. At the moment, he is not bothered by the alleged chthonic stagnation. “It’s probably unrelated to life on the surface, but we really don’t know what’s going on,” he says. “We have to figure it out.”

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