Is There a Scientist in the House?

via Livescience:

"By examining sediment layers, the team found that the crater impact appears to have occurred about 300,000 years before the K-T boundary, with virtually no effects to biota.

"There is essentially no extinction associated with the impact," Keller said.

I have a simple question - how the hell is that possible?

How is it possible that a meteor impact of that size could be nothing more than a blip in the biosphere? Doesn't that go against nearly everything we've been told about the danger of asteroids?

I mean, I can understand the desire to make your theory The LAST WORD on dinosaur extinctions, but to totally dismiss the other theory seems... irresponsible.

Is there a scientist in the house who could clear up this mystery? Have we been misled about the relative dangers of asteroids and volcanos?