There is a debate in the scientific community about how the last extinction event went down. The standard answer since the late 80s has been suddenly via asteroid, but there is a growing theory that it was a more gradual event caused primarily by volcanoes in India erupting over hundreds of thousands of years.
The article goes into the acrimonious feud between the various proponents of the respective theories.
This was a fun read for me because I had just assumed the consensus was pretty set. Interesting view of the scientific method working its magic (even if the participants are behaving less than ideally).