In ice cores from both ends of the planet, scientists have discovered evidence of an extreme solar storm that struck Earth around 9,200 years ago, and strangely, it seemed to have occurred during a period when the Sun should have been rather quiet. The Sun regularly throws off solar flares and bursts of plasma called coronal mass ejections (CMEs), and if they collide with Earth they can affect our planet’s magnetosphere. Most of the time the only result is stronger aurorae, but powerful CMEs can damage satellites, disrupt communications, and even shut down electrical transmission lines. Radioactive isotopes like beryllium-10...