The mysterious iron ball at the center of the Earth may have stopped spinning and reversed direction

• Earth's inner core may have paused and reversed its spin, a new study suggests.
• Earthquakes and nuclear blasts can send seismic waves through the mysterious solid-iron core.
• Those waves hint that the core changed direction in the 1970s, and may be undergoing another reversal today.

Living on Earth's surface, we only see about 0.5% of the planet. Deep below the crust, then the hot rock mantle, then the liquified outer core, lies one of our planet's biggest mysteries: the solid iron core at the center.