Has the Earth’s inner core slowed its rotation?

Earthquake data suggests the inner core stopped spinning faster than the rest of the planet in 2009. However, the results leave some questions unanswered.

Thousands of kilometers beneath our feet, something very strange may be happening inside the Earth: Many scientists believe that the Earth’s inner core is spinning faster than the rest of the planet — but at some point over the past decade , a recent study suggests it stopped doing so .

“We were quite surprised,” say Beijing University seismologists Yi Yang and Xiaodong Song, who published the results in Nature Geoscience. The work could help unravel the many mysteries of Earth’s interior, such as the role of the inner core in maintaining the magnetic field and the rate of rotation of the entire planet — and thus the length of a day. In the end, however, it represents only the latest attempt to explain the inner core’s unusual rotation, and the final word on the matter may not yet have been spoken.

Secret inside

Researchers discovered the Earth’s inner core in 1936 while studying how seismic waves from earthquakes propagate throughout the planet. Changes in the speed of the waves revealed that the Earth’s core, which is around 7000 kilometers in diameter, must have a fixed centre. This consists mainly of iron and is in turn surrounded by a shell of liquid iron and other elements. As the iron from the outer core crystallizes at the surface of the inner core, the density of the liquid changes, creating swirling motions that perpetuate the Earth’s magnetic field.


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