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Earth’s core slowing down

The Earth's layers, each rotating at different speeds

Rost-9D / Getty Images

The Earth’s inner core, a rigid sphere of iron and nickel, appears to be slowing down. It is surrounded by a layer that behaves like a liquid, the outer core, and rotates at a different speed than the mantle and crust, the outermost layers of the planet. Sometimes the inner core rotates faster than the mantle and crust, sometimes slower. By analyzing the seismic waves (generated by earthquakes) that crossed the planet in the last six decades, seismologists from Peking University in China identified signs that the core is decelerating in relation to the outermost layers. Between 2009 and 2011, the inner core, which previously rotated slightly faster than the crust and mantle, started to rotate at a similar speed to the more outer layers. More recently, it has started to spin in the opposite direction. The consequences? Nothing catastrophic. There may be subtle changes in the Earth’s magnetic field, which shields the planet from radiation from space, as well as fractions of a millisecond changes in the length of the days (Nature Geoscience, January 23).