The inner core of the Earth, a solid ball with a radius of about 1,220 km, is now rotating in the opposite direction compared to nearly a century ago, scientists have discovered.
A study led by Dr. John Vidale, Dean’s Professor of Earth Sciences at the University of Southern California’s Dornsife College of Letters, Arts and Sciences, has confirmed a slow deceleration of Earth’s inner core rotation, to the point where it is now moving backward.
This inner core was first discovered by Danish seismologist Inge Lehmann in 1936, and its movement, rotation speed, and direction have been the subject of debate for decades.
According to Dr. Lauren Waszek, a senior lecturer of physical sciences at James Cook University in Australia, the phenomenon of differential rotation of the inner core was proposed in the 1970s and ’80s, with seismological evidence emerging in the 1990s.
In 2023, some scientists suggested that the inner core, which once spun faster than Earth, had begun to spin slower. Initially, it was believed that the core's rotation matched Earth’s spin, but it later decelerated and started moving backward relative to the fluid layers around it.
Researchers now believe this change in speed and direction is part of a 70-year cycle.
"We’ve been arguing about this for 20 years, and I think this nails it. I think we’ve ended the debate on whether the inner core moves, and what’s been its pattern for the last couple of decades,” said Vidale.
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