Small fluctuations in the length of Earth's 24-hour day can be explained by a battle between forces generated by the movement of the planet's metallic core. The finding, reported today in Nature1, suggests that geophysicists could be on the right track to understanding mysterious structures in Earth's deep interior. The planet's rate of rotation changes subtly over time, giving rise to variations in the length of our day that are on the order of just a few milliseconds over decades. Geophysicists measure these changes by observing Earth's position relative to distant cosmic objects. Researchers have suspected that these variations are linked to interactions between Earth's core and its rocky mantle, but it wasn't clear what forces were involved, says Mathieu Dumberry, a geophysicist at the University of Alberta in Edmonton, Canada. Scientists know that it is the core 'that's responsible for these decadal changes. But how does it do it'' he says. 'This is the part that's unclear.'...
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