Yves Gallet balanced on a steep rocky slope in northeast Siberia, a turquoise river leisurely wending across the undulating landscape that sprawled below. But Gallet, of France’s Institut de Physique du Globe de Paris, had his face turned toward the rocks with one goal in mind: deciphering the history of Earth’s magnetic field.

This protective bubble shields Earth from radiation that’s constantly streaming from the sun. In the planet’s 4.6-billion-year history, the field has frequently flipped, swapping magnetic north and south, and some research suggests that another flip may be on the geological horizon. While fears of a looming geomagnetic apocalypse are overblown, a magnetic reversal could have many damaging impacts, from increased radiation exposure to technological disruptions, which makes understanding