Quote from bearice:
SAN FRANCISCO â Huge volcanic eruptions that belched sulfur into the air for around 10,000 years could have killed the dinosaurs, according to new evidence unearthed by geologists.
Evidence is accumulating that it wasnât an asteroid that did the beasts in, but volcanoes â the first real challenge the extinction theory has met in three decades.
A combination of studies on dinosaur fossils, magnetic signatures in rocks and the timing of the disappearance of different species suggest it was volcanoes, not an asteroid, that caused the dinosaursâ extinction.
http://www.wired.com/wiredscience/2008/12/deccantraps/#
Those who have investigated this have pointed out that that asteroid impact was large enough to start earthquakes and, you know, volcanoes.
It wasn't just big, it was freakin' ridiculously huge. So much so that they have hypothesized that volcanoes spat crap out on the other side of the world from where that asteroid hit.