EARTH’S inner core is rotating more slowly and has changed direction, experts have confirmed.
The inner core is a solid iron-nickel sphere around the size of the Moon.
It floats 3,000 miles beneath the planet’s surface, suspended in a sea of metal called the outer core.
And a paper published last month in Nature has found evidence that the core is “backtracking,” in line with trends observed over decades.
Scientists have struggled to understand the core’s behavior for years. While its movement has been changing, the mechanism driving it has remained unclear.
Scientists hypothesize that the core rotated in time with the Earth before slowing and moving backward relative to the liquid around it.
The new paper also supports a theory that the change is part of a long-observed pattern of slowing and accelerating.
But what exactly is prompting this change?
The researchers used information from earthquakes and Soviet nuclear tests to analyze the inner core’s movement.
Specifically, they compiled seismic data from 121 earthquakes occurring in the same place at different times between 1991 and 2023.
“The matching waveforms reveal times at which the inner core re-occupies the same position, relative to the mantle, as it did at some time in the past,” the scientists wrote.
This pattern “demonstrates that the inner core gradually super-rotated from 2003 to 2008, and then from 2008 to 2023 sub-rotated two to three times more slowly back through the same path.”
The inner core’s movement is driven by the Earth’s magnetic field, which causes it to spin.
At the same time, the mantle and fluid outer core exert their own forces on the ball of iron, creating a push-and-pull effect.
Scientists believe this has caused the inner core to slow down over time.
The paper cites evidence that it has been moving slower than the Earth’s mantle and crust, rather than faster, since 2010.
The findings may affect the length of a day on Earth – but there’s a catch.
Experts say this change would be imperceptible in one lifetime, totaling just thousandths of a second.
However, the paper adds to a growing body of evidence that the length of days is changing.
What do experts say about the length of Earth’s days?
Here Mackenzie Tatananni, Science and Technology reporter at The U.S. Sun, walks through the different theories.
There is a growing body of evidence that Earth’s days are getting longer, but experts disagree on just what’s causing it.
They agree that days are getting longer by between 1.7 and 1.8 milliseconds every 100 years.
And researchers at the University of Texas at Austin blame the tides.
As the Earth spins on its axis, this determines the amount of sunlight crossing its face and, in turn, the length of days, which we know is 24 hours.
But the Moon’s gravity tugs at the side of Earth that is closest to it, creating what are known as “tidal bulges.”
Since Earth spins faster than the Moon orbits it, these bulges travels ahead of the Moon’s relative position and create friction along the seafloor that impedes the planet’s rotation.
Researchers at The University of Wisconsin-Madison agree that days are lengthening, but say it’s driven by changes in the Moon’s distance from Earth.
The gravitational pull from other celestial bodies affects Earth’s movement, causing variations in its axial spin.
These shifts are known as Milankovitch cycles and play a role in the amount of sunlight that reaches Earth.
Over 1 billion years ago, the Moon was closer to the our planet, and some researchers say this is why a day lasted just over 18 hours.
While a combination of factors is the most likely explanation, scientists continue to study these day-length changes and publish papers containing their research.
Previous studies have determined that days may eventually stretch to 25 hours.
The change amounts to roughly 1.8 milliseconds per century, or a one-minute increase every 3.3 million years.
This means it could take 200 million years before another hour is tacked on to the day.
Experts believe this change is the result of the friction produced by tides, which has been slowing Earth‘s rotation over time.
Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
