Earth's Inner Core Slowing Down, Could Trigger Change In Length Of Day

A recent 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 noted that this slowdown might alter the length of a day by fractions of a second.

The Earth's inner core - a solid sphere composed of iron and nickel - is encased in the liquid outer core, held in place by gravity. These two cores, along with the mantle and crust, make up Earth's three main layers. Since the core is physically inaccessible, scientists study it by analysing seismograms, which are recordings of waves generated by earthquakes.

"When I first saw the seismograms that hinted at this change, I was stumped," says John Vidale, professor of Earth Sciences at University of Southern California.

He added, "But when we found two dozen more observations signalling the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades".

The slowing of the inner core is a contentious topic among scientists, with some studies even suggesting that it rotates faster than the surface of the Earth. The inner core's rotation is influenced by the magnetic field of the outer core and gravitational forces within the mantle. It is now believed that the inner core is reversing its direction relative to the surface due to its slower rotation compared to 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 said.

An earlier study published in Nature indicated that climate change-induced melting of ice in Greenland and Antarctica is affecting global timekeeping by slowing Earth's rotation. Duncan Agnew, a geophysicist at the University of California San Diego, explained that as the liquid core's rotation slows, the solid Earth compensates by rotating faster. This has led to a decrease in the number of 'leap seconds' needed to adjust Coordinated Universal Time (UTC) since 1972. Leap seconds are occasionally added to account for irregularities in Earth's rotation.

The recent study analysed seismic data from 121 repeating earthquakes in the South Sandwich Islands, occurring between 1991 and 2023. These islands, located in the South Atlantic Ocean, frequently experience violent earthquakes. Data from Soviet nuclear tests between 1971 and 1974, as well as various French and American nuclear tests, were also included in the analysis.