The Greenhouse Effect
Another popular theory the greenhouse effect theory first proposed by Dewey McLean. He and many others believed that a intense period of volcanic eruption and small asteroid impact was the cause however Mclean believed this was a minor event and what followed was the result of the extinction of the dinosaurs.
Mclean says that the asteroid that formed the Chicxulub crater happed 300,000 years before the death of the dinosaurs. According to Mclean the fateful dinosaur killer happed somewhere else on earth and is still yet to be discovered.