Earth's Inner Core May Be Less Solid Than Previously Believed

Earth's Inner Core May Be Less Solid Than Previously Believed
by Clarence Oxford
Los Angeles CA (SPX) Feb 12, 2025

A new study by USC scientists suggests that the surface of Earth's inner core may be undergoing structural changes, challenging the long-held belief that it is a solid sphere. The findings, published in Nature Geoscience, provide fresh insights into the dynamic nature of the planet's deep interior.

For decades, scientists have debated the behavior of Earth's inner core, with much of the focus centered on its rotation. However, John Vidale, Dean's Professor of Earth Sciences at USC Dornsife College of Letters, Arts and Sciences and the study's principal investigator, noted that his team was not initially seeking to redefine the core's physical nature.

"What we ended up discovering is evidence that the near surface of Earth's inner core undergoes structural change," Vidale explained. This observation suggests that topographical activity may be influencing the inner core's rotation, contributing to subtle shifts in the length of a day and possibly linking to the core's gradual slowing.

A New Perspective on the Inner Core

Situated roughly 3,000 miles beneath the Earth's surface, the inner core is encapsulated by the liquid outer core and has long been assumed to be a solid mass. The USC researchers originally set out to investigate the inner core's slowing motion but made an unexpected discovery along the way.

"But 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."

The study relied on seismic waveform data, specifically 121 repeating earthquakes recorded from 42 locations near the South Sandwich Islands between 1991 and 2024. When comparing the waveforms at seismic stations near Fairbanks, Alaska, and Yellowknife, Canada, the team noticed unusual seismic properties at the latter location, indicating an unexpected change within the inner core.

"At first the dataset confounded me," Vidale admitted. It was only after refining the resolution technique that the team realized they were observing additional physical activity within the core.

Evidence of Core Deformation

The study suggests that the inner core may undergo viscous deformation, altering its shape and shifting at its shallow boundary. The primary driver of this structural change is likely the interaction between the inner and outer core.

"The molten outer core is widely known to be turbulent, but its turbulence had not been observed to disrupt its neighbor, the inner core, on a human timescale," Vidale noted. "What we're observing in this study for the first time is likely the outer core disturbing the inner core."

This discovery sheds light on the intricate processes occurring deep within the Earth and could enhance our understanding of the planet's thermal and magnetic fields.

Research Report:Annual-scale variability in both the rotation rate and near surface of Earth's inner core