Scientists from the University of Southern California (USC) have confirmed that the Earth's inner core is rotating more slowly than the planet's surface. The ground-breaking research raises important questions about planetary mechanics and may have a significant effect on both the stability of Earth's magnetic field and the duration of our days, Science Alert reported.
The study published in Nature provides evidence that the inner core began to decrease its speed around 2010, marking the first time in approximately 40 years that it is moving slower than the Earth’s mantle. Notably, the inner core — a super-hot, super-dense sphere of iron and nickel—is located over 4,800km beneath our feet.
For the study, John Vidale and his colleagues analysed readings from 121 repeating earthquakes recorded between 1991 and 2023 around the South Sandwich Islands in the South Atlantic. They also used data from Soviet nuclear tests conducted between 1971 and 1974, as well as French and American nuclear tests from other studies on the inner core.
''When I first saw the seismograms that hinted at this change, I was stumped. But when we found two dozen more observations signalling the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades. Other scientists have recently argued for similar and different models, but our latest study provides the most convincing resolution,'' said Mr Vidale, Dean's Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences.
Mr Vidale explained that the slowing of the inner core's rotation is caused by the turbulent movement of the surrounding liquid outer core, which generates the Earth's magnetic field, and the gravitational pulls from dense regions in the overlying rocky mantle.
This could eventually alter the entire planet's rotation, prolonging our days. Mr Vidale said the backtracking of the inner core may alter the length of a day by fractions of a second: "It's very hard to notice, on the order of a thousandth of a second, almost lost in the noise of the churning oceans and atmosphere."
The team now wants to chart the trajectory of the inner core in even greater detail to reveal exactly why it is shifting. "The dance of the inner core might be even more lively than we know so far," Mr Vidale said.