New research suggests fragments of a disintegrating comet may have exploded in the atmosphere over North America approximately 13,000 years ago. This event, potentially linked to the Younger Dryas cooling period, is proposed as a cause for the extinction of mammoths and other Ice Age megafauna, as well as the disappearance of the Clovis culture. Evidence cited includes microscopic grains of "shocked" quartz found at three key archaeological sites, which indicate extreme heat and pressure consistent with a cosmic impact or atmospheric explosion.