Earth’s inner core is slowing down, shows study

The inner core began to decrease its speed around 2010, moving slower than the Earth’s surface. Credit: University of Southern California.

Scientists from the University of Southern California (USC) have discovered that Earth’s inner core is slowing down.

This new finding, published in the journal Nature, shows that the inner core’s rotation has slowed down relative to the planet’s surface.

This movement has been a topic of debate among scientists for the past 20 years, with some previous studies suggesting that the inner core rotates faster than the Earth’s surface.

The USC study now provides clear evidence that around 2010, the inner core began to rotate more slowly.

John Vidale, a professor at USC, was initially puzzled when he saw the seismograms indicating this change. “When I first saw the seismograms that hinted at this change, I was stumped,” he said.

But after finding similar patterns in more than two dozen observations, the team concluded that the inner core had indeed slowed down for the first time in many decades.

Other scientists have proposed different models, but this study offers the most convincing evidence so far.

The inner core, a solid sphere made of iron and nickel, is about the size of the moon and is located more than 3,000 miles beneath the Earth’s surface. It is surrounded by a liquid iron-nickel outer core.

Because it is so deep, scientists cannot directly observe the inner core. Instead, they study it using seismic waves from earthquakes.

In this study, Vidale and Wei Wang from the Chinese Academy of Sciences used seismic data from repeating earthquakes, which are seismic events that occur in the same location and produce identical seismograms.

They analyzed data from 121 such earthquakes recorded around the South Sandwich Islands between 1991 and 2023. They also used data from Soviet nuclear tests in the 1970s and repeated French and American nuclear tests from other studies.

Vidale explained that the slowing of the inner core is caused by the movement of the liquid iron outer core that surrounds it, which generates Earth’s magnetic field, as well as gravitational pulls from the dense regions of the Earth’s mantle above it.

The effect of this change on Earth’s surface is still uncertain. Vidale mentioned that the slowing inner core might slightly alter the length of a day by fractions of a second, but it is barely noticeable due to the constant movement of the oceans and atmosphere.

The USC scientists plan to continue their research to better understand the inner core’s movements and the reasons behind its shifting. “The dance of the inner core might be even more lively than we know so far,” Vidale said.

This discovery adds a new layer to our understanding of the Earth’s inner workings and could have important implications for the study of our planet’s geology and magnetic field.