Dec. 12, 2008 -- It was a dying on a scale never seen before or since on Earth. The slaughter was everywhere; the fertile ocean and balmy supercontinent Pangea were transformed into killing fields, littered with the bodies of ancient animals. By the time the dust had settled on the Permian-Triassic mass extinction 250 million years ago, 90 percent of life on the planet had been snuffed out.
Now a new theory suggests the catastrophe was set in motion 15 million years earlier, deep in the Earth. On the edge of the molten outer core, a plume of super-hot material began rising through the mantle, upsetting convection in the core and throwing the planet's magnetic field into disarray.
The weakening of Earth's magnetic field exposed the surface to a shower of cosmic radiation, says Yukio Isozaki of the University of Tokyo. He believes the radiation broke nitrogen in the atmosphere into ions that acted as seeds for clouds enshrouding the planet.
