Around 13,000 years ago, three things happened at once: (1) Global temperature suddenly stopped rising and plunged back to ice age-frigidity. (2) The Western Hemisphere’s largest mammals, including the horse, camel, woolly mammoth, saber-toothed cat, and dozens more, went extinct. And (3) the uniquely beautiful stonework of the early American Clovis people disappeared from the archeological record. <br> <br>For the past half-century, scientists have struggled to explain the three events. Were they independent of each other, or could they have had a common cause? Then in 2007, researchers reported finding minuscule ET melt droplets and nanodiamonds at the geologic layer that records the three events, evidence, they said, that the common cause was the impact of a giant comet. Opposition to the impact hypothesis was swift and severe, as opponents reported that they could not replicate the evidence and decried the hypothesis as pseudoscience, no better than UFOs, perpetual energy, and cold fusion. Yet over the last decade, scientists have replicated the original evidence and uncovered a wealth of new supporting data. One eminent geologist describes the hypothesis as possibly "the most important in the Earth Sciences since plate tectonics." <br> <br>In language accessible to non-scientists, Deadly Voyager tells the story of how an extraterrestrial event many thousands of years ago changed earth and human history — and how a scientific claim can be thoroughly rejected, only to re-emerge strengthened.