A recent study has found “unambiguous evidence” that Earth’s inner core began to slow its rotation relative to the planet’s surface in 2010, potentially altering the length of a day by fractions of a second. The inner core, composed of solid iron and nickel, is surrounded by the liquid outer core and held in place by gravity. Researchers study the core using seismograms, which record earthquake waves. John Vidale, a professor at the University of Southern California, noted that the core’s slowdown is the first in decades, with findings published in Nature.
The inner core’s rotation has been a contentious topic, with some scientists suggesting it spins faster than the surface. The spin is influenced by the magnetic field in the outer core and gravitational forces within the mantle. The study indicates that the inner core is now reversing its direction, rotating slower than the mantle for the first time in around 40 years. This conclusion offers a compelling resolution to ongoing debates in the scientific community, as noted by Vidale.
The researchers examined seismic data from 121 earthquakes between 1991 and 2023 in the South Sandwich Islands, a seismically active area. They also included data from Soviet, French, and American nuclear tests. This comprehensive analysis supports the findings of earlier studies, such as one by Duncan Agnew, which linked the slowdown in Earth’s rotation to climate change-induced ice melt. These changes have led to fewer ‘leap seconds’ being added to Coordinated Universal Time (UTC) in recent decades, reflecting the Earth’s inconsistent rotation speed.
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