A groundbreaking study has provided “unambiguous evidence” that the Earth’s inner core has been slowing its rotation relative to the planet’s surface since 2010. Researchers indicate this deceleration could alter the length of an Earth day by mere fractions of a second.
Understanding the inner Core
The Earth’s inner core, a solid sphere composed of iron and nickel, is encased within the liquid outer core of molten metals, both held in place by gravitational forces. Together, these form one of the planet’s three primary layers, along with the mantle and crust. Due to its inaccessibility, scientists study the core by analyzing seismograms from earthquake waves.
“When I first saw the seismograms hinting at this change, I was stumped,” said John Vidale, a professor of Earth Sciences at the University of Southern California. “But with two dozen more observations confirming the same pattern, the result was inescapable. The inner core had slowed down for the first time in decades,” Vidale, the study’s corresponding author, reported in the journal Nature.
Scientific debate
The deceleration of the inner core’s rotation has sparked considerable debate within the scientific community. Some studies suggest it may even rotate faster than the Earth’s surface. The inner core’s spin is influenced by the magnetic field of the outer core and gravitational effects within the mantle. Current findings suggest the inner core is reversing and backtracking relative to the surface for the first time in about 40 years.
“Other scientists have proposed various models, but our latest study provides the most convincing resolution,” Vidale stated. Earlier this year, a study in Nature linked climate change-driven ice melt in Greenland and Antarctica to a slowdown in Earth’s rotation. Geophysicist Duncan Agnew from the University of California San Diego noted that the liquid core’s deceleration caused the solid Earth to rotate faster, reducing the need for ‘leap seconds’ in Coordinated Universal Time (UTC).
For their research, scientists analyzed seismic data from 121 repeating earthquakes between 1991 and 2023 in the South Sandwich Islands, known for their seismic activity. The study also incorporated data from Soviet nuclear tests (1971-1974) and various French and American nuclear tests, providing a comprehensive analysis of the inner core’s behavior.
This study offers crucial insights into the complex dynamics of the Earth’s inner core, shedding light on its impact on our planet’s rotation and day length. As researchers continue to explore these phenomena, our understanding of Earth’s inner workings will undoubtedly deepen.