Scientists have found new evidence that the Earth’s inner core, a dense metal ball deep within the planet, may not be perfectly solid and is changing shape. Researchers say its outer layer has changed shape in recent decades, raising new questions about the dynamics of the planet’s center.
The inner core, made mostly of iron and nickel, is about 1,500 miles wide and sits beneath layers of rock and molten metal. A recent study suggests that forces from the outer core, the liquid layer surrounding it, may be pulling on the inner core, causing slight movements.
John Vidale, a professor of earth sciences at the University of Southern California, said this shifting may be due to turbulence in the outer core or gravitational forces from the surrounding mantle. The research team published its findings on Feb. 10 in the journal Nature Geoscience.
Inner core does not rotate at the same speed
Scientists have long known that the inner core does not rotate at the same speed as the rest of the Earth. Studies show that its speed has varied over time. A few decades ago, the core appeared to be spinning slightly faster than the outer layers. Now, research suggests it is slowing down.
The Earth consists of several layers. The crust, where humans live, is the thinnest. Below it is the mantle, a layer about 1,800 miles thick that slowly moves, shifting continents over time. Beneath the mantle lies the liquid outer core, which surrounds the solid inner core.
Earth's Inner Core is Changing Shape 🚨
Scientists have just made a mind-blowing discovery-Earth’s inner core, a scorching-hot solid metal ball, is deforming over time.
1/ Core Reversal & Deformation
Researchers recently confirmed that Earth’s inner core reversed its spin-now,… pic.twitter.com/Js3TD2Bopl— SciGod (@SciGodX) February 10, 2025
Since scientists cannot physically explore the Earth’s deep interior, they rely on earthquake vibrations to gather information. These vibrations, known as seismic waves, move at different speeds and directions depending on the density of the layers they pass through.
For this study, researchers analyzed earthquakes from the South Sandwich Islands, a volcanic chain in the South Atlantic Ocean. This region experiences frequent earthquakes, sometimes with nearly identical strength and location as earlier ones. By comparing these “earthquake pairs” recorded over time, scientists tracked changes deep inside the planet.
Seismic signals reveal clues
The team examined over 100 earthquake pairs recorded between 1991 and 2004 using seismometers more than 8,000 miles away—one in Fairbanks, Alaska, and the other in Yellowknife, Canada.
Seismic waves from the earthquakes should have produced identical readings at both locations. While Fairbanks recorded consistent signals, the data at Yellowknife showed unexpected differences.
Because Yellowknife is slightly closer to the South Sandwich Islands, the waves it detected did not travel as deep into the inner core as those reaching Fairbanks. This suggested that something had changed near the outer edge of the inner core, affecting how the waves moved through it.
Vidale explained that turbulence in the outer core or gravitational forces from dense areas in the mantle may have shifted the inner core’s boundary. These subtle deformations could be responsible for the changes in seismic signals.
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