This pause and change in direction lasts around 60 to 70 years and could explain a number of natural phenomena, research published in Nature Geoscience on Monday suggests.

For those of us who live blissfully unaware of the giant metal ball at the heart of our planet, the inner core is 75 per cent the size of the moon and is about as hot as the sun’s surface.

Really, it is “a planet within a planet,” said Xiaodong Song, a seismologist at China’s Peking University, and one of the study’s authors, “so how it moves is obviously very important.”

But don’t worry, this spin cycle shift won’t have any apocalyptic consequences: Song and his colleague Yi Yang are simply trying to figure out the machinations of the Earth’s innards and how they impact the rest of the world.

The inner core, located some 3,000 miles beneath our feet and surrounded by a liquid outer core, is largely a mystery since it can’t be directly sampled. This means specialists like Song and Yang observe seismic waves from earthquakes and nuclear weapon tests to discover more about its properties.

So far, we understand that the ball – made predominantly of iron and nickel – is 1,520 miles long and has a temperature of around 5,200C ( 9,392F).

And whilst scientists know that it can spin at different speeds and directions to the rest of the Earth because of that outer liquid core, they are still trying to work out how fast it rotates and whether this varies over time.

However, progress is being made on that front, and Yang and Song’s new paper reveals “surprising observations that indicate the inner core has nearly ceased its rotation in the recent decade.”

They found that the core “may be experiencing a turning-back in a multidecadal oscillation, with another turning point in the early 1970s.”

The researchers explained in an email toVice that “there are two major forces acting on the inner core”: one is electromagnetic, the other gravitational.

“If the two forces are not balanced out, the inner core will accelerate or decelerate,” they told the site.

“Both the magnetic field and the Earth’s rotation have a strong periodicity of 60-70 years. We believe that the proposed 70-year oscillation of the inner core is driven by the electromagnetic and gravitational forces.”

So what does this mean for us?

Not a huge amount, to be honest. If this 70-year cycle exists, it’s likely to only have subtle effects on the surface of the planet, such as causing minor shifts in the Earth’s magnetic field or altering the length of a day by a fraction of a millisecond.

Despite all of Song and Yang’s hard work, theirs is just one of a number of theories explaining the irregular way in which waves reach the Earth’s core, and the mystery may never be solved.

“It’s certainly possible we’ll never figure it out,” fellow seismologist John Vidale told the New York Times.

But, he added: “I’m an optimist. The pieces are going to fall into place someday.”