The inner core of the Earth can be the backbone of its rotation

Our planet may have a recent change of heart.

Earth’s inner core may sometimes stop rotating around the mantle and surface, researchers report on January 23 Nature Geoscience. Now, the direction of rotation of the inner core may be preposterous — part of what may be a roughly 70-year cycle that can influence the length of Earth’s days and its magnetic field — though some researchers are skeptical.

“We see strong evidence that the inner core rotates faster than the surface; [but] It almost stopped by around 2009, says geophysicist Xiaodong Song of Peking University in Beijing. “Now move slowly”[ing] on the contrary “

Such a profound turnaround might sound prodigious, but the Earth is volatile.SN: 1/13/21). Break through the ever-moving crust and you’ll enter the titanic mantle, where behemoth masses of rock flow in succession over millions of years, sometimes bursting to peel away the upper crust.SN: 1/11/17, SN: 3/2/17, SN: 2/4/21). Go deeper and you will reach the Earth’s liquid core. Here, a rotating stream of metal spindles opposes our planet’s magnetic field (SN: 9/4/15). And in the middle of that molten, solid metal ball you’ll find about 70 percent as wide as the moon.

This is the inner core (SN: 1/28/19). The study suggested that this solid core rotates inside the liquid core forced outward by the magnetic torque of the outer core. The researchers also argued that the mantle could apply an immense gravitational pull to an erratic fracture in the rotation of the inner core, which could cause it to oscillate.

Evidence for a fluctuating internal rotation core first emerged in 1996. Paul Richards, a geophysicist at Columbia University in Palisades, NY, and Song, then also at Lamont-Doherty, reported that over a three-decade period, seismic waves from earthquakes take varying amounts of time to travel through the Earth’s solid core.

The researchers speculated that the inner core rotates at different speeds than the mantle and crust, causing the time differences. The planet rotates about 360 degrees in a day. From their calculations, the researchers estimated that the inner core rotates, on average, about 1 degree per year faster than the rest of the Earth.

However, other researchers have questioned that conclusion, with some suggesting that the core focus of Song and Richard’s evaluation is slower or not drawn at all.

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

Before 2009, seismic waves generated by sequences and repeating pairs of earthquakes—which are multiple and duplicated—traveled through the inner core at varying rates. This means that waves from the frequent movements of the inner core pass through different parts, and that the inner core rotates at a different pace than the rest of the Earth, aligning with previous research by Songs.

But around 2009, the differences in travel times disappeared. That suggested the inner core stopped rotating around the mantle and crust, Yang says. After 2009, these differences returned, but the researchers guessed that the waves were passing through parts of the inner core that suggested they were now rotating in the opposite direction with respect to the rest of the Earth.

The researchers then looked at duplicate records of the 1964 Alaskan earthquake. While the inner core appeared to be spinning steadily for most of that time, it appears to have undergone another revolution in rotation in the early 1970s, the researchers say.

Song and Yang concluded that the inner core can oscillate with a periodicity of about 70 years – changing directions every 35 years or so. Because the inner core is gravitationally connected to the mantle and magnetized to the outer core, researchers say these characteristic oscillations could explain the 60- to 70-year variations in the length of Earth’s days and the behavior of the planet’s magnetic field. However, more work is needed to pinpoint the mechanisms that are responsible.

But not all researchers are on board. Yang and Song “identif”[y] this recent 10 years [that] it has less activity than before, and I think it’s probably fixed,” says geophysicist John Vidale of the University of Southern California in Los Angeles, who was not involved in the research. But beyond that, says Vidale, things are contentious.

In 2022, he and a colleague reported that seismic waves from nuclear tests show that the inner core can reverse its rotation every three years or so. Meanwhile, other researchers have proposed not to move the inner core at all. But they say that changes in the shape of the surface of the inner core could explain the differences in the travel times of the wave.

Future observations will probably explain the discrepancies between these studies, says Vidale. For now the unrestrained chthonically stands. “In all likelihood, that’s related to life on the surface, but we don’t actually know what’s going on,” he said. “We need to figure it out.”