On the flip, in record time (Image: G.Glatzmaier/Los Alamos National Laboratory/P.Roberts/UCLA/SPL)

SOME 16 million years ago, north became south in a matter of years. Such fast flips are impossible, according to models of the Earth’s core, but this is now the second time that evidence has been found.

The magnetic poles swap every 300,000 years, a process that normally takes up to 5000 years. In 1995 an ancient lava flow with an unusual magnetic pattern was discovered in Oregon. It suggested that the field at the time was moving by 6 degrees a day – at least 10,000 …