Scientists confirm that the rotation of the Earth’s inner core has slowed down and is already spinning more slowly than the surface

Scientists at the University of Southern California (USC) have shown that the Earth’s inner core is receding, that is, slowing down, relative to the planet’s surface, as shown in new research published in Nature.

The motion of the inner core has been debated by the scientific community for two decades, with some research indicating that the inner core rotates faster than the planet’s surface. The new USC study provides unequivocal evidence that the inner core began to slow down around 2010, moving slower than the Earth’s surface.

When I first saw the seismograms hinting at this change, I was stumped.said John Vidale, Dean Professor of Earth Sciences at USC Dornsife College of Letters, Arts and Sciences. But when we found two dozen more observations pointing to 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 compelling resolution.

The inner core is considered to be inverting and receding relative to the planet’s surface because it is moving slightly slower rather than faster than Earth’s mantle for the first time in about 40 years. Relative to its speed in previous decades, the inner core is slowing down.

The inner core is a solid sphere of iron and nickel surrounded by the liquid outer core of iron and nickel. About the size of the moon, the inner core lies more than 3,000 miles beneath our feet and presents a challenge to researchers: it cannot be visited or seen. Scientists must use seismic waves from earthquakes to create representations of the movement of the inner core.

Vidale and Wei Wang of the Chinese Academy of Sciences used repetitive waveforms and earthquakes in contrast to other research. Repetitive earthquakes are seismic events that occur in the same location and produce identical seismograms.

In this study, the researchers collected and analyzed seismic data recorded around the South Sandwich Islands from 121 repeat earthquakes that occurred between 1991 and 2023. They have also used data from twin Soviet nuclear tests between 1971 and 1974, as well as French repeat nuclear tests. and Americans from other inner core studies.

Vidale said the slowing of the inner core’s speed was caused by the churning of the surrounding liquid iron outer core, which generates Earth’s magnetic field, as well as by gravitational pulls from dense regions of the overlying rocky mantle. .

The impact on the Earth’s surface

The implications of this change in inner core motion for the Earth’s surface can only be speculated. Vidale said the inner core recoil could alter the length of a day by fractions of a second: It is very difficult to notice, on the order of a thousandth of a second, almost lost in the noise of the oceans and the churning atmosphere.

Future research by USC scientists aims to chart the trajectory of the inner core in greater detail to reveal exactly why it is changing.

The inner core dance could be even livelier than we know so farVidale said.