New scientific findings suggest that a large comet may have exploded over North America 12,900 years ago, explaining riddles that scientists have wrestled with for decades, including an abrupt cooling of much of the planet and the extinction of large mammals.
The discovery was made by scientists from the University of California at Santa Barbara and their colleagues. James Kennett, a paleoceanographer at the university, said that the discovery may explain some of the highly debated geologic controversies of recent decades.
The period in question is called the Younger Dryas, an interval of abrupt cooling that lasted for about 1,000 years and occurred at the beginning of an inter-glacial warm period.