A long-running scientific debate over the fate of the mammoths is gaining fresh momentum, as new research adds weight to the idea that a massive cosmic event disrupted life on Earth nearly 13,000 years ago. Some scientists now believe that fragments of a disintegrating comet exploded in the atmosphere above North America, setting off a chain reaction that may have contributed to the extinction of mammoths, mastodons and other large Ice Age animals and possibly the disappearance of one of the continent’s earliest human cultures. In a study published in PLOS One, a research team led by UC Santa Barbara emeritus earth scientist James Kennett reports new findings from three well-known archaeological sites linked to the Clovis culture. The locations – Murray Springs in Arizona, Blackwater Draw in New Mexico and Arlington Canyon on California’s Channel Islands – have long been central to discussions about North America’s late Ice Age extinctions. At all three sites, the researchers discovered microscopic grains of “shocked” quartz, a material typically associated with extreme heat and pressure. Kennett notes that these sites …