An analysis of a stalagmite from the depths of a cave in China has unveiled clues about an event in Earth's history when its magnetic field flipped back and forth in a geological blink. Not only was this rapid wobble a surprise, a similarly abrupt shift in the near future would almost certainly pose big problems for societies heavily reliant on digital technology. You only need a compass to know we're surrounded by a force that lines up with the globe's axis, pointing steadfastly towards the Arctic while its tail shows the way to the Antarctic. This unseen bubble of magnetism is generated by swirling currents of charged particles deep under our feet. But we still know surprisingly little about its formation or how the field evolves. Fortunately for curious geologists, the magnetic field leaves an indelible mark on Earth's crust. Frozen in place inside solidified igneous rock, magnetised minerals can provide clues on the field's orientation prior to their cooling. So imagine the