The leading theory is that this physical change arises from the inner core's interaction with the more chaotic outer core, though other ideas include inner core convection or interactions with structures in the lower mantle.

Love the air you're breathing, the water you're drinking, and the life you're living? Thank Earth's inner core. The intense heat of this ball of nickel and iron drives the movement of the liquid outer core, which produces Earth's magnetic field -- that invisible lifeline that protects the planet (and all of its inhabitants) from harmful solar radiation.

Despite the inner core's starring role in making life on Earth possible, scientists are still discovering fundamental facts about this ball of metal. A new study from scientists at the University of Southern California (USC) pored over decades' worth of seismograms collected from Fairbanks, Alaska, and Yellowknife, Canada, to try and answer some lingering questions.

The research team's original intent was to gather more data from its discovery last year -- that the rotation of the inner core may be slowing. However, John Vidale, a seismologist from USC and lead author of a new study published in Nature Geoscience, found evidence that appeared to refute an established "fact" about the inner core.

Maybe, this solid ball of metal wasn't as solid as we previously thought.

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

Analyzing the interior of the Earth is tricky business. Without the aid of unobtainium to explore the Earth's depths (a la 2003's The Core), scientists instead have to rely on seismograms that track seismic waves as they travel through the Earth. This study took a closer look at 121 repeating earthquakes near the South Sandwich Islands in Antarctica and analyzed the waveforms from receiver-array stations in the northern U.S. and Canada.

Vidale said that the uncharacteristic properties of one particular dataset from the Canadian station "confounded" him, and after further investigation, Vidale and his team surmised that the inner core was changing shape. This means that the surface of the inner core is likely more viscous than we previously realized, and that this physical change likely occurs due to interactions with the more geologically chaotic 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 said in a press statement. "What we're observing in this study for the first time is likely the outer core disturbing the inner core."

Other theories suggest that this deformation could be caused by interactions with structures in the lower mantle (which separates the core from the Earth's crust), or perhaps even convection within the inner core itself. "It's really hard to tell," Vidale told New Scientist.

Vidale and his team's work joins a growing chorus of research indicating that the Earth's core isn't a solid as it seems. Two studies from 2023 found that the core likely contained layers of liquid iron and might best described as "how butter is soft in your kitchen," one researcher said. It's becoming increasingly clear that the physical structure of Earth's core is far from settled science.

Continued observations of seismograms in search of physical changes in the surface of the outer core will hopefully piece together a more complete picture of the life-sustaining geology occurring in the heart of our home planet.