Comet explosions in North America 13,000 years ago did not end the prehistoric human culture known as Clovis - the earliest well-established human culture in the North American continent, named after the town in New Mexico (USA) where distinct stone tools were first found in the 1920s and 1930s.
     Researchers from Royal Holloway University, together with Sandia National Laboratories and 13 other universities across the USA and Europe, deny that a large impact or airburst caused a significant and abrupt change to the climate, arguing that other explanations must be found for the culture's apparent disappearance.
     No 'appropriately sized' impact craters from that time period have been discovered, and no shocked material or any other features of impact have been found in sediments. Samples presented in support of the impact hypothesis were contaminated with modern material, and no physics model can support the theory.
     "The theory has reached zombie status," said Professor Andrew Scott from the Department of Earth Sciences at Royal Holloway. "Whenever we are able to show flaws and think it is dead, it reappears with new, equally unsatisfactory, arguments."

Edited from PhysOrg, UPI (30 January 2013)