Causes of Extinctions
Several hypotheses attempt to explain the cause of the K–T boundary that led to the massive extinction. These hypotheses center on either impact events or increased volcanism; some include elements of both. The current overall consensus among paleontologists based on accumulated evidence is that the primary cause for the extinction was an asteroid impact that occurred about 65.5 Ma, severely disrupting the Earth's biosphere.
Read more about this topic: Cretaceous–Paleogene Extinction Event