Did the eruption of an enormous volcano blot out the rays of the sun all over the planet 75,000 years ago? Did this mammoth volcanic blast cause a "deep freeze" on the Earth that might be repeated in the future? This unsettling documentary from "Nova" goes hot on the trail of the distressing scientific discovery that uncovers evidence similar megavolcanoes may threaten the future of the globe. 56 min. Widescreen; Soundtracks: English, DVS.