Day length may change as Earth's inner core slows down since 2010: study

New Delhi:

A new study has provided “unequivocal evidence” that Earth's inner core has begun to slow down its rotation since 2010, compared to the planet's surface.

The researchers said the deceleration could change the length of a day on Earth by fractions of a second.

The Earth's inner core, a solid ball made of iron and nickel, is suspended within a liquid outer core (made of molten metals) and held in place by gravity. Together, the inner and outer core make up one of the planet's three layers – the other two being the mantle and the crust.

Because it is physically inaccessible, researchers typically study the core by analyzing recordings of waves from earthquakes – seismograms.

“When I first saw the seismograms indicating this change, I was puzzled,” said John Fidell, a professor of geosciences at the University of Southern California in the US.

“But when we found twenty other observations pointing to the same pattern, the conclusion was inevitable. The inner core had slowed down for the first time in many decades,” said Vidal, who is also the corresponding author of the study published in the journal Nature.

The deceleration of the inner core is hotly debated in the scientific community, with some studies even suggesting that it rotates faster than the Earth's surface.

It is known that the rotation of the inner core is affected by the magnetic field generated in the outer core and the effects of gravity within the Earth's mantle.

However, the inner core is thought to be reversing and receding relative to the surface, due to it rotating more slowly than the mantle for the first time in about 40 years.

“Other scientists have recently discussed similar and different models, but our latest study provides the most convincing solution,” Vidal said.

A study published earlier this year, in the journal Nature, found that climate change-induced melting of ice in Greenland and Antarctica is affecting global timekeeping by slowing the Earth's rotation.

The author, Duncan Agnew, a geophysicist at the University of California San Diego, showed that the Earth's liquid core was slowing down in its rotation. To counteract the effects, the solid Earth was rotating faster, Agnew said.

However, this has reduced the need to add “leap seconds” to UTC in recent decades, according to Agnew.

Since 1972, it has been necessary to add a “leap second” once every few years, due to irregularities in Coordinated Universal Time (UTC) arising from the fact that the Earth does not always rotate at the same speed.

In the latest study, researchers looked at seismic data recorded from 121 recurrent earthquakes — multiple earthquakes occurring at the same location — between 1991 and 2023 in the South Sandwich Islands, a remote archipelago in the South Atlantic Ocean. The islands are vulnerable to violent earthquakes.

Data from dual Soviet nuclear tests between 1971 and 1974, along with multiple French and American nuclear tests from other studies of the inner core, were also included in the analysis.

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