Were the early Dark Ages triggered by a natural event of cataclysmic proportions around 535 A.D.? Science writer David Keys theorizes that "a loud bang"-a volcanic explosion equal to two billion Hiroshima-size bombs"-caused an environmental calamity affecting human civilization from Mongolia to Constantinople, precipitating plague, famine, death, great migration, the Anglo-Saxon victory over the Celts-and perhaps even the rise of Islam.