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how often is a supernova event likely to occur close enough to Earth to cause a mass-extinction event? Well, estimates vary but a mid-range estimate is that a supernova event will occur within 30 light years of Earth on average every 200 million years or so. If that estimate is accurate we have another question to ask: why are we here?
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If the Universe Is Teeming with Aliens ... WHERE IS EVERYBODY?: Seventy-Five Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life
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