The Cretaceous-Paleogene (K-Pg) mass extinction, formerly called the Cretaceous-Tertiary mass extinction, was the fifth major mass extinction event of the Phanerozoic eon. This event took place roughly 66 million years before the present. According to the Alvarez hypothesis, this mass extinction was primarily triggered by a massive bolide impact, probably a carbonaceous chondrite asteroid or a comet, in the southern Caribbean Sea. Volcanic activity, particularly the eruption of the Deccan Traps in India, also played a role in this extinction. Some scientists have attributed the extinction to other factors throughout history, but today, impact and volcanism are thought to be the most significant factors. Approximately 75% of all animal species, including all non-avian dinosaurs, became extinct in the ensuing impact winter, which lasted at least a decade.
