Earth’s Inner Core Is Changing Shape, Study Finds, Indicating Even More Dynamic Shifts Deep Within Our Planet

Deep at the center of the Earth, our planet’s inner core is spinning, growing and—according to new research—shape-shifting.

A new study published Monday in the journal Nature Geoscience found evidence that the Earth’s inner core—a hot, mostly solid ball of iron roughly 1,500 miles wide—deforms at its boundary with the liquid outer core. “Even though that inner core part is really solid, [this boundary] is really soft,” explains study co-author Guanning Pang, a geophysicist at Cornell University, to Kasha Patel at the Washington Post. “Maybe as soft as jelly.”

Scientists can’t get anywhere near the Earth’s core, so they have to use other sources of information to understand it. The research team used data from 121 earthquakes gathered between 1991 and 2023 and analyzed their seismic waves, which had passed through Earth’s inner core as they traveled from the remote South Sandwich Islands in the southern Atlantic Ocean to North America.

They compared earthquakes that had occurred at the same sites at different times to see if their wave signals changed over the years. The team focused on quakes that had taken place when the core was rotated into the same position, in an effort to zero in on the effect of its shape alone.

“They’re basically exactly the same earthquakes that hit years apart—the same place, the same fault,” explains John Vidale, a seismologist at the University of Southern California and lead author of the study, to the Washington Post.

The Earths Inner Core Mystery

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The scientists found unexplained variations in some of those waves, pointing to physical deformations in the inner core. Specifically, seismic waves that had traveled through the outermost region of the core were the ones that appeared variable, suggesting the shape-shifting is happening around the inner core’s exterior boundary.

“Basically, the wiggles are different,” Vidale says to Kenneth Chang at the New York Times. “The most likely thing is the outer core is kind of tugging on the inner core and making it move a little bit.”

While scientists have theorized about the existence of these movements, this study provides some of the best data yet about the inner core’s changes, reports Science’s Hannah Richter. “This is kind of the first time we’ve seen the evidence for this kind of motion,” says Vidale to the Washington Post. “The surface of the inner core is moving around in ways we hadn’t detected and still don’t understand very well.”

The study follows earlier research by the same team that found the inner core is slowing its spin. Their previous paper, published in Nature last summer, suggested the rotating core changes its speed in a cycle, switching between spinning faster and slower than the Earth’s surface. Some scientists disputed that idea, however, arguing that fluctuations in the core’s shape—without any change in speed—could explain their data. This new study proposes that changes in both shape and speed are at play.

“After decades of research and debates, we are coming to an ever-clearer picture of the changing inner core,” says Xiaodong Song, a seismologist at Peking University in China who was not involved in the work, to Nature News’ Alexandra Witze.

These alterations deep in the Earth don’t have much of an impact on our lives at the surface, and for now, the broader significance of the new study isn’t clear. But Vidale tells Clara Harter at the Los Angeles Times that he hopes the work can help uncover more of the inner core’s mysteries.

“We hope it has broader implications,” he says. “The reason we do this is we like to solve riddles, and the stranger and harder the riddle that we can solve, the happier we are.”

Sara Hashemi | READ MORE

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.