Humans have long speculated about how the world will end. During the cold war the focus was on nuclear annihilation. Now the focus is on the threat of terrorists getting access to bioweapons. Corey S. Powell lists 30 threats that could end the world—or human life—as we know it. Environmental toxins, a biotech disaster or an ecosytem collapse could make life impossible. But Powell thinks most of his 30 doomsday scenarios are unlikely (Discover, October).