Scientists accidentally discover Earth's inner core is less solid than expected

For a long time, scientists thought the Earth's inner core was a solid ball of metal, sort of like a planet within a planet that sits some 3,000 miles (4,828 kilometers) below the surface.

However, researchers from the University of Southern Carolina (USC) now say they discovered — almost by accident — that the Earth's inner core may be much more malleable.

John Vidale, Dean's Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences, who was the new study's principal investigator, said in a statement that the researchers "didn't set out to define the physical nature of the inner core."

Originally, the USC scientists were tracking how our planet's inner core speed of rotation is decreasing, because previous research found that the core is slowing down. The method for charting this involves studying seismic waveform data from earthquakes.

The team used the data from 121 repeating earthquakes between 1991 and 2024; the chosen events happened across 42 different locations near the uninhabited South Sandwich Islands that are situated north of Antarctica.

The USC scientists were studying the waveforms when they came upon some surprising data that contradicted our previous understanding of Earth's inner core. A dataset of waveforms held some uncharacteristic properties the team wasn't expecting to see.

"As I was analyzing multiple decades' worth of seismograms, one dataset of seismic waves curiously stood out from the rest," Vidale said. "Later on, I’d realize I was staring at evidence the inner core is not solid."

Once Vidale's team improved the resolution technique, they found the seismic waveforms "represented additional physical activity of the inner core." So, the data led them to believe that the inner core might be moving around a bit, rather than staying completely solid.

"What we ended up discovering is evidence that the near surface of Earth's inner core undergoes structural change," Vidale said.

According to the researchers, the structural change may relate to the inner core's slowing and could lead to a better understanding of the Earth's thermal and magnetic fields. What's more, the change might have "minutely altered the length of a day."

The research was published on Feb. 10 in the journal Nature Geoscience.