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

Scientists at the University of Southern California (USC) have shown that Earth’s inner core is moving away, or slowing down, relative to the planet’s surface, according to a new study published in the journal Nature.

The motion of the inner core has been debated by the scientific community for two decades, with some studies suggesting that the inner core rotates faster than the planet’s surface. A 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 seismograms hinting at this change, I was puzzled.said John Vidale, chair of the Department of Geosciences in the USC Dornsife College of Letters, Arts and Sciences. But when we discovered two dozen more observations pointing to the same pattern, the result was inevitable. The inner core slowed for the first time in decades. Other scientists have recently argued for similar and different models, but our latest study provides the most compelling solution yet.

The inner core is thought to be flipping and moving away relative to the planet’s surface as it moves slightly slower rather than faster than Earth’s mantle for the first time in about 40 years. Compared to the speed of previous decades, the inner core is slowing down.

The inner core is a solid sphere of iron and nickel surrounded by a liquid outer core of iron and nickel. The moon-sized inner core lies more than 3,000 miles below our feet and poses a challenge for researchers: it cannot be visited or seen. Scientists must use seismic waves from earthquakes to create an idea of ​​the movement of the inner core.

Vidale and Wei Wang of the Chinese Academy of Sciences used repeating waveforms and earthquakes, unlike other studies. Repeat earthquakes are seismic events that occur in the same location and produce identical seismograms.

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

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

Impact on the Earth’s surface

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

Future research by USC scientists aims to map out the trajectory of the inner core in more detail to find out exactly why it is changing.

The dance of the inner core may be even more alive than we know so far.Vidale said.