Has Earth’s inner core stopped its strange spin?

Around 2009, Earth’s solid-iron inner core might have stopped rotating faster than the rest of the planet. Researchers studied seismic waves generated by US nuclear test blasts during the cold war, and later by earthquakes, to discover that the inner core started spinning faster than the mantle after 1971, then slowed back down. The results could help to shine light on mysteries including what part the inner core plays in maintaining the planet’s magnetic field and in affecting the speed of the whole planet’s rotation — and thus the length of a day. But the latest study is unlikely to have the final word on the disputed topic.