ScienceDaily (Jan. 27, 2009) — New data disproves the recent theory that a large comet exploded over North America 12,900 years ago, causing a shock wave that travelled across North America at hundreds of kilometres per hour and triggering continent-wide wildfires.
Dr Sandy Harrison from the University of Bristol and colleagues tested the theory by examining charcoal and pollen records to assess how fire regimes in North America changed between 15 and 10,000 years ago, a time of large and rapid climate changes.
Their results provide no evidence for continental-scale fires[*]...
[*] This being one of the predictions made by the Younger Dryas impact theory.
Ah well, Pre-History just got a bit more boring.