(CNN) — A new study suggests that the rotation of Earth’s inner core may have stopped and even reversed.
Earth is made up of crust, mantle and inner and outer core. The solid inner core lies about 5,000 km below the Earth’s crust and is separated from the semi-solid mantle by the liquid outer core, which allows the inner core to rotate at speeds other than Earth’s rotation.
With a radius of over 3,500 km, Earth’s core is roughly the size of Mars. It is composed mostly of iron and nickel, and contains about one-third of Earth’s mass.
In research published Monday in the academic journal Nature Geoscience, Yi Yang, an associate research scientist at Peking University, and Xiaodong Song, a professor at the same university, studied seismic waves from earthquakes that have passed through Earth’s inner core. Earth has been following a similar trajectory since the 1960s to measure how fast the inner core is spinning.
The result was unexpected. Since 2009, seismic records, which previously varied over time, showed little difference. This, he said, suggested that the rotation of the inner core had stopped.
“We make surprising observations showing that the inner core has nearly stopped rotating over the last decade and may have undergone a reversal,” they wrote in the study.
Song continued, “When you look at the decade between the 1980s and 1990s, you see a clear change, but when you look from 2010 to 2020, you don’t see much change.”
The spin of the inner core is driven by the magnetic field generated in the outer core and balanced by the gravitational influence of the mantle. Knowing how the inner core spins could shed light on how these layers and other processes interact deep within Earth.
However, the speed of this rotation, and its variation, are debated, says Hroje Talcic, a geophysicist at the Australian National University who was not involved in the study.
“The inner core never completely shuts down,” he said. The study’s finding, he said, “means that the inner core is now more in sync with the rest of the planet than it was a decade ago, when it was spinning slightly faster.”
“Nothing catastrophic is happening,” he said.
Song and Yang argue that, according to their calculations, a small imbalance in the electromagnetic and gravitational forces could slow and even reverse the rotation of the inner core. They believe this is part of a seven-decade cycle, and that the tipping point occurred in the early 1970s, before being detected in their data around 2009/2010.
“The study’s data analysis is robust,” said Talcic, author of the book “The Earth’s Inner Core: Revealed by Observational Seismology.” However, the study’s findings “should be taken with caution” because “more data and innovative methods are needed to shed light on this exciting problem.”
Song and Yang agreed on the need for further investigation.
study of the center of the earth
Tkalcic, who devotes an entire chapter of his book to the rotation of the inner core, suggested that the inner core cycle lasts 20 to 30 years, rather than the 70 proposed in the latest study. He explained why these variations occur and why it is so difficult to understand what happens in the innermost regions of the planet.
“The objects of our study are buried thousands of kilometers beneath our feet,” he said.
“We use geophysical estimation methods to infer Earth’s intrinsic properties, and caution should be exercised until multidisciplinary findings confirm our hypothesis and conceptual framework,” he explained.
“Seismologists can be thought of as doctors who study the internal organs of patients’ bodies using limited or imperfect equipment. Therefore, despite progress, our picture of Earth’s interior remains hazy, and we Still in the search phase.