The biggest extinctions in our planet's history have been blamed, at various times, on asteroids, gas-emitting microbes or volcanic eruptions. The five mass die-offs destroyed most animals and plants on Earth, including the dinosaurs 66 million years ago. New evidence points strongly to cataclysmic eruptions as the real culprits.Highly accurate rock dates pin such eruptions to the same times as four of the major extinctions and tie the explosions to lethal changes in the atmosphere, as the illustrations here show.