The researchers said the slowing of Earth’s inner core could lead to changes in the length of the day.
New Delhi:
A new study provides “unequivocal evidence” that the rotation speed of Earth’s inner core has started to slow since 2010, compared to the planet’s surface.
The researchers said the slowdown could change the length of a day on Earth by just a split second.
The Earth’s inner core is a solid sphere made of iron and nickel that floats in a liquid outer core (made of molten metals) and is held in place by gravity. Together, the inner and outer cores form one of the Earth’s three layers; the other two are the mantle and crust.
Because the Earth’s crust is physically inaccessible, researchers typically study it by analysing records of waves emitted by earthquakes, known as seismograms.
“When I first saw the earthquake records suggesting this change, I was puzzled,” said John Bedale, professor of geosciences at the University of Southern California in the US.
“But when we found 24 more observations showing the same pattern, the conclusion was inevitable: the inner core’s velocity had slowed for the first time in decades,” said Vidale, corresponding author of the study published in Nature.
The slowing of the inner core is a topic of intense scientific debate, with some studies even suggesting that the inner core may rotate faster than the Earth’s surface.
The rotation of the inner core is known to be influenced by the magnetic field generated in the outer core and by the influence of gravity within the Earth’s mantle.
However, for the first time in about 40 years, the inner core is rotating slower than the mantle, and it is believed that the inner core has reversed and is retreating relative to the surface.
“Other scientists have recently proposed similar or different models, but our latest work offers the most plausible solution,” Vidal said.
A study published in the journal Nature earlier this year found that melting ice in Greenland and Antarctica due to climate change is slowing down the Earth’s rotation, affecting time measurements on Earth.
Study author Duncan Agnew, a geophysicist at the University of California, San Diego, showed that Earth’s liquid core is slowing down its rotation, and to counteract this, the solid Earth is spinning faster, Agnew said.
But Agnew said this has resulted in fewer “leap seconds” having to be added to Coordinated Universal Time (UTC) in recent decades.
Since 1972, it has been necessary to add a “leap second” every few years because of irregularities in UTC caused by the Earth not always rotating at the same speed.
In the latest study, researchers looked at recorded seismic data from 121 repeating earthquakes (multiple earthquakes occurring at the same location) that occurred between 1991 and 2023 in the South Sandwich Islands, a remote archipelago in the South Atlantic Ocean that is prone to violent earthquakes.
Data from two Soviet nuclear tests conducted between 1971 and 1974, as well as multiple French and American nuclear tests conducted in other studies of the inner core, were also included in the analysis.
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