What is weakening Earth’s invisible shield? Magnets have the power to attract and repel—sometimes on a massive scale. The Earth’s molten core—a violent mix of searing heat, crushing pressure, and a billion trillion tons of liquid iron—creates an invisible shield that surrounds the globe, guarding against a constant barrage of deadly radiation from space. But over the last few decades, the Earth’s magnetic field has weakened dramatically, intriguing scientists across the globe. The power generate...