Deep underneath our feet, a giant may have started moving against us.
Earth's inner core, a hot iron ball, almost as the size of Pluto, has stopped spinning in the same direction as the rest of the planet and might even be rotating the other way, according to research.
Roughly 5,000 kilometres (3,100 miles) below the surface we live on, this "planet within the planet" can spin independently since it floats in the liquid metal outer core.
Exactly how the inner core rotates has been a matter of debate between scientists for a long period.
What tiny we know about the inner core, mostly, comes from measuring the tiny differences in seismic waves, which are created by earthquakes or sometimes nuclear explosions, as they pass through the middle of the Earth.
In quest of tracking the inner core's movements, the new research, published in the journal Nature Geoscience newly, analysed seismic waves from repeating earthquakes over the last six decades.
The study's authors, Xiaodong Song and Yi Yang of China's Peking University, apparently said that they found that the inner core's rotation "came to a near halt around 2009 and then turned in an opposite direction".
"We believe the inner core rotates, relative to the Earth's surface, back and forth, like a swing," they told to AFP.
"One cycle of the swing is about seven decades", meaning it changes direction roughly every 35 years, they added.
They said it appeared that earlier, it changed its direction in the early 1970s and anticipated the next about-face would be in the mid-2040s.
The researchers said that this rotation roughly lines up with the changes in what is called the "length of day", small variations in the exact time it takes Earth to rotate on its axis.