Scientists have determined that Earth’s inner core may be moving in an opposite direction compared to nearly a century before.
The inner core is solid, whereas the outer core is liquid. As the solid core spins, it creates currents of molten metals, which help generate Earth’s magnetic field. This protects the planet’s surface from the Sun’s harmful radiation.
It has long been thought that this “spinning dance” between the liquid and solid elements of the Earth’s core at approximately 3,000 miles below the surface follows the same eastward rotation as the rest of the planet but at a much faster rate. However, some researchers suggest that the rotation has stopped or even started to turn in the opposite direction.
This is what scientists in China have argued in their study published on January 23. They based their findings on analyses of earthquake-driven seismic waves passing through the planet.
“We see strong evidence that the inner core has been rotating faster than the surface, [but] by around 2009 it nearly stopped,” said geophysicist Xiaodong Song of Peking University in Beijing, according to Science News.
“Now it is gradually moving in the opposite direction,” she continued.
The research team analyzed repeated seismic waves from the early 1990s and compared these patterns to the Alaskan seismic records of South Sandwich Islands doublets dating back to 1964.
They concluded that the shift seemed to be “associated with a gradual reversal of the inner core as part of an oscillation” that takes about 70 years. This operates like a swing, meaning that the inner core changes direction every 35 years.
The study’s authors also claimed that the change in the rotation could trim the length of a day, though only by a fraction of a millisecond. They did not believe life on the surface would be affected by this change.
While they suggested that this reversal could be caused by “gravitational coupling and the exchange of angular momentum from the core and mantle to the surface,” other scientists are not so sure.
“The changes they noticed are valid although what’s actually happening isn’t so clear,” said Dr. John Vidale, a geophysicist at the University of Southern California.
“They have a very good analysis and the theory they put in the papers is probably as good as anything at the moment,” he continued, “but there are several competing ideas as well.”