Scientists have discovered that Earth’s inner core is slowing down relative to the planet’s speed … [+]
New research suggests Earth’s inner core has been slowing down for 14 years, which could mean the length of a day is increasing slightly.
Published this month in NatureThe findings run counter to previous research indicating that the inner core rotates faster than the planet’s surface.
Inner Core
About 3,000 miles below the surface, Earth’s inner core is a sphere of solid iron-nickel. It’s about the same size as the moon and surrounded by a liquid iron-nickel outer core, which generates Earth’s magnetic field. Above this outer core is the rocky mantle and, finally, the crust.
Because it cannot be seen or sampled, Earth’s inner core is notoriously difficult to study. The easiest way to study the core is to obtain data from seismic waves produced by earthquakes. In this case, researchers used seismic data from earthquakes and nuclear tests to analyze the movement of the inner core.
WConvincing resolution
Scientists from the University of Southern California and the Chinese Academy of Sciences have discovered that Earth’s inner core is slowing down relative to the planet’s surface. This change in the inner core’s motion occurred around 2010. The paper suggests that the slowdown is the result of churning in the liquid iron outer core and gravitational tugs from parts of the mantle.
The research shows that the inner core is moving a little slower rather than faster than Earth’s mantle for the first time in about 40 years. “The inner core has slowed down for the first time in many decades,” said John Vidale, professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences. “Other scientists have recently argued for similar and different models, but our latest study provides the most convincing resolution.”
The inner core began to slow down around 2010, moving more slowly than the Earth’s surface.
Lost in the noise
The slowing of the inner core is expected to have implications for the length of a day, simply because the slower it moves, the greater the drag factor on the speed at which Earth rotates. Since one rotation takes 24 hours and equals one day, a slower inner core means it will take longer for Earth to complete one rotation. However, this is expected to change by only fractions of a second. “It’s very difficult to notice, on the order of a millisecond, almost lost in the noise of the churning oceans and atmosphere,” Vidale said.
Seismic Data
The study used seismic data from 121 earthquakes between 1991 and 2023 near the South Sandwich Islands, a chain of uninhabited volcanic islands in the South Atlantic Ocean. It also used data from nuclear tests conducted by the US, France and the USSR between 1971 and 1974.
“When I first saw the seismograms that suggested this change, I was perplexed,” Vidale said. “But when we found two dozen more observations signaling the same pattern, the result was inevitable.
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