- The Earth’s dense inner core is now moving backwards relative to the surface
- Researchers say this could change the length of days by a fraction of a second
If it feels like the days are dragging on more than ever, it might not just be your boring job that’s to blame.
A new study has revealed that changes to the Earth’s inner core may be increasing the length of days.
Earth’s dense metal core is now backtracking relative to the planet’s surface, according to a team from University of Southern California.
By looking at earthquake data, they found that the inner core began to slow around 2010 and is now moving backwards, subtly affecting the Earth’s rotation in space.
However, don’t expect to enjoy more hours in the day just yet – as the researchers say the change may be very hard to notice.
Earth is made up of four major layers: the crust, mantle, outer core and inner core.
At the very centre of the planet, 3,000 miles (4,800km) beneath our feet is the inner core – a superheated ball of solid iron and nickel about the size of the moon.
Since the surrounding outer core is entirely liquid, this dense metal sphere is free to spin under the pull of Earth’s magnetic field and the gravitational influence of the outer layers.
For years, many scientists believed that the inner core was spinning faster than the Earth’s surface.
However, Professor John Vidale, an Earth scientist at the University of Southern California, says the core has now slowed down and has begun to move backwards.
‘The dance of the inner core might be even more lively than we know so far,’ he said.
Without any way of directly observing the Earth’s inner core, the researchers relied on data collected from seismic events.
In particular, Professor Vidale and his co-authors focussed on events called repeating earthquake – seismic events which occur at the same location to produce identical patterns in recordings called seismograms.
In addition to 121 natural events recorded around the South Sandwich Islands, the researchers also used human events like the Soviet twin nuclear tests between 1971 and 1974.
As seismic events send shockwaves through the Earth, the condition and location of each of the layers will subtly change the shape of the wave that scientists record.
When the waveforms of repeating waves match, this reveals moments when the inner core is in the exact same position relative to the Earth’s outer layers.
Researchers discovered sets of seismograms in which a repeating earthquake would occur, change, and then match again a few years later.
For example, the data showed that an earthquake recorded in March 2003 was slightly different to a 2009 earthquake in the same location, but identical to one recorded in 2020.
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What that shows is that the inner core moved relative to the surface between 2003 and 2009, only to return back into the same position by 2020.
This means that the inner core must have been rotating forward relative to the surface until some time in 2010 at which point it slowed and began to move backwards.
Professor Vidale said: ‘When I first saw the seismograms that hinted at this change, I was stumped.
‘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.’
This slowing could be caused by the churning of the liquid iron core which generates the Earth’s magnetic field as well as gravitational tugs from unusually dense areas in the mantle.
While the effects that this will have are almost impossible to predict Professor Vidale says that it could change the length of the day by a very small amount.
He says: ‘It’s very hard to notice, on the order of a thousandth of a second, almost lost in the noise of the churning oceans and atmosphere.’
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.
