LOS ANGELES (KTLA) – Researchers at the University of Southern California say they’ve unraveled the mystery of why Earth’s inner core has been slowing, gradually altering the length of a day.
For decades, scientists assumed Earth’s moon-sized core was made of solid iron and nickel and moved in lock with the planet’s surface. In 2010, however, the core began to show signs of slowing for the first time in documented history.
“As I was analyzing multiple decades’ worth of seismograms, one dataset of seismic waves curiously stood out from the rest,” said John Vidale of USC Dornsife College of Letters, Arts and Sciences. “Later on, I’d realize I was staring at evidence the inner core is not solid.”
The study analyzed seismic data, including 121 repeating earthquakes at 42 locations near Antarctica’s South Sandwich Islands, from 1991 to 2024. Researchers then looked at waveforms from receiver stations in Alaska and Canada.
According to the university, the data showed “uncharacteristic properties” the team had never seen before, indicating Earth’s inner core was changing shape and moving, first faster and then slower than the rest of the planet.
“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. “What we’re observing in this study for the first time is likely the outer core disturbing the inner core.”
USC researchers said the findings shed light on the reasons why the length of a day, typically measured as 24 hours or 86,400 seconds, has not been constant. Scientists believe a day lasted just 21 hours 600 million years ago.
Other factors include the Earth’s magnetic field, the tidal effects of the sun and moon, and the distribution of mass on the planet.
The study was published Monday in Nature Geoscience.
