Scientists say the Earth's core is slowing - here's what it means

A new study says the Earth's core has slowed during the past two decades, and it could have a measurable impact on the planet.

The University of Southern California said new evidence proved the Earth's inner core - a solid, moon-sized ball of iron-nickel at the centre of the planet - had been decreasing its speed since 2010.

"When I first saw the seismograms that hinted at this change, I was stumped," Dean's Professor of Earth Sciences John Vidale said.

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"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 inner core is considered to be reversing relative to the planet's surface due to moving slightly slower instead of faster than the Earth's mantle - the massive layer between the planet's solid crust and the outer core - for the first time in about 40 years.

Relative to its speed in previous decades, the inner core is slowing down, USC said in a release.

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Vidale said the inner core's slowing speed was caused by the churning of the liquid iron outer core, which generates Earth's magnetic field, as well as gravitational tugs from the dense regions of the overlying rocky mantle.

The implications of the findings can only be speculated on, researchers said.

Vidale said the backtracking of the inner core may alter the length of a day - but just by fractions of a second.

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"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," he said.

The USC scientists now hope to establish exactly why the inner core is shifting.

"The dance of the inner core might be even more lively than we know so far," Vidale said.

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