Scientists have discovered that our planet's core has been rotating at a slower rate for nearly 15 years -- and it could mean longer days for some.

The new research from the University of Southern California, now published in Nature, noticed that the Earth's inner core was moving slower than the surface, termed "backtracking," and has been doing so since 2010.

"When I first saw the seismograms that hinted at this change, I was stumped," said researcher John Vidale.

"But when we found two dozen more observations signaling the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades."

Specifically, it's the first time in nearly 40 years that the core was moving slower than the Earth's mantle -- a planetary layer sandwiched between the topside crust and core.

Researchers measured seismic readings from earthquake activity from 1991 to 2023 along with nuclear tests done by the US, France, and Soviet Union from 1971 to 1974. From that data, Vidale assessed that the inner core's slower speed was the result of liquid iron churning within the Earth's outer core.

That liquid metal is responsible for generating Eearth's magnetic field in addition to aspects of gravity related to the mantle.

At this point, though, what is to be for the planet as a result is only speculation, according to USC.

However, Vidale says the length of our days could be extended -- at an incredibly down-to-Earth rate of a split second.

"It's very hard to notice, on the order of a thousandth of a second, almost lost in the noise of the churning oceans and atmosphere."

Still, he's excited about what future research holds.

"The dance of the inner core might be even more lively than we know so far."