There May Be Something Big Going On in Earth's Center

If you were born before 2009, you lived through a time when the center of the Earth stopped spinning. So say seismologists, who believe they've discovered a mysterious cycle that sees the inner metal core of the planet speed up, then decelerate and ultimately come to a standstill before beginning to spin in the opposite direction. The idea of a solid metal core within a liquid outer core was proposed in 1936, but it's only in the last three decades that seismologists have found evidence that the inner core spins at varying speeds, altering the travel time of seismic waves, per the New York Times. Now, a new study suggests the inner core changes its direction every few decades. It also suggests we experienced a pause between 2009 and 2011.

Seismologists at Peking University in Beijing, China, looked at seismic waves that reached into the depths of the planet as far back as the 1960s, determining the inner core wasn't spinning in the early 1970s. It then began spinning eastward with the Earth's surface, picking up speed until it was rotating faster than the surface, before slowing down and finally stopping its rotation between 2009 and 2011, according to the study. It suggests the core is now spinning slowly in the opposite direction and will continue spinning faster and faster until it slows down and finally comes to a stop in the 2040s, completing a roughly 70-year cycle.

This is thought to involve pressures from the magnetic field generated by the outer core, countered by gravitational forces of the surrounding mantle, though those on Earth’s surface may not notice anything beyond minor tweaks in the length of a day, based on the time it takes Earth to rotate on its axis, per AFP. The research, published Monday in Nature Geoscience, follows a 2022 study, based on seismic waves recorded in 1969 and 1971, that suggested the inner core changes direction much more quickly, about once every six years. But the idea of a spinning inner core remains controversial. Some believe there are other explanations for the twisting of seismic waves, such as physical changes to the surface of the inner core, per Nature. (More seismology stories.)