A groundbreaking study has delivered “unambiguous evidence” that the Earth’s inner core has been slowing its rotation relative to the planet’s surface since 2010. Researchers indicate that this deceleration might alter the length of a day on Earth by fractions of a second.
The Earth’s inner core, a solid sphere composed primarily of iron and nickel, is encased within a liquid outer core made of molten metals. This core system is held in place by gravity and forms one of the planet’s three fundamental layers, alongside the mantle and crust.
Due to its inaccessibility, scientists study the inner core by analyzing seismograms—recordings of seismic waves generated by earthquakes, NDTV Report.
“When I first saw the seismograms that hinted at this change, I was stumped,” said John Vidale, a professor of Earth Sciences at the University of Southern California. “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,” added Vidale, the corresponding author of the study published in Nature.
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The slowing of the inner core is a topic of intense debate within the scientific community. Some studies have suggested that the inner core rotates faster than the Earth’s surface.
The spin of the inner core is influenced by the magnetic field generated in the outer core and gravitational interactions within the Earth’s mantle. Recent findings suggest that the inner core is now reversing and backtracking relative to the surface, rotating slower than the mantle for the first time in approximately 40 years.
“Other scientists have recently argued for similar and different models, but our latest study provides the most convincing resolution,” Vidale noted.
A study published earlier this year in Nature revealed that climate change-driven melting of ice in Greenland and Antarctica is affecting global timekeeping by slowing down Earth’s rotation. Duncan Agnew, a geophysicist at the University of California San Diego, demonstrated that the Earth’s liquid core was decelerating its rotation.
To compensate, the solid Earth is rotating faster, resulting in fewer ‘leap seconds’ needing to be added to Coordinated Universal Time (UTC) in recent decades. Since 1972, a ‘leap second’ has been added approximately once every few years to account for irregularities in UTC due to Earth’s variable rotation speed.
For the latest study, researchers examined seismic data from 121 repeating earthquakes—multiple quakes occurring in the same location—recorded between 1991 and 2023 in the South Sandwich Islands, a remote archipelago in the South Atlantic Ocean known for its seismic activity.
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The analysis also incorporated data from twin Soviet nuclear tests conducted between 1971 and 1974, as well as multiple French and American nuclear tests from other studies of the inner core.
The discovery of the Earth’s inner core slowing down has significant implications for our understanding of the planet’s internal dynamics and timekeeping. As researchers continue to study seismic data and refine their models, the scientific community will gain deeper insights into the intricate processes governing Earth’s rotation and its impact on our daily lives.