The Effort

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When dark comet UD3 was spotted near Jupiter's orbit, its existence was largely ignored. But to individuals who knew better -- scientists like Benjamin Schwartz, manager of NASA's Center for Near-Earth Object Studies -- the threat this eight-kilometer comet posed to the survival of the human race was unthinkable. The 150-million-year reign of the dinosaurs ended when an asteroid impact generated more than a billiontimes the energy of an atomic bomb.
What would happen to Earth's seven billion inhabitants if a similar event were allowed to occur?