writes "The NSF has released a study that strongly implicates a comet explosion over North America roughly 13000 years ago. Researchers at the University of Californina at Santa Barbara with the help of a National Science Foundation grant visited many Clovis sites around North America. The abrupt cooling trend of that time is known as the Younger Dryas or 'big freeze' and the collapse of the Clovis has been the subject of much debate over recent years. Samples from 12 Clovis period sites yielded high concentrations of Iridium, nano-diamonds, and buckyballs (fullerenes) that contain gases which indicate extraterrestrial origins.
From the article: 'The team concluded that the impact of the comet likely destabilized a large portion of the Laurentide ice sheet, causing a high volume of freshwater to flow into the north Atlantic and Arctic Oceans.'"