This guy doesn't pussyfoot around like those science noobs with delicate turns of phrase and tactfully ambiguous allusions to what to expect from a supervolcano eruption.
Supervolcanos are the extinction cycle driver. Everybody knows it, even if you can't get a grant to study that fact. If you think nuclear war will be bad, wait until you see a planet recovering from a supervolcano eruption.
Warm blooded squishy mammals have a lot of vulnerabilities in these regards - if they don't build Vaults. The entire article is quotable, so I encourage you to read it for yourself.
Remember, we pass through the galactic plane every 65 million years. The next scheduled pass will be dead center in December 2012. The last time the planet was dead center was called the K-T Boundary extinction event, almost exactly 65 million years ago. Most of the other grand extinction cycles coincide perfectly with this 65 million year interval.
It's the volcanism, stupid. Tell the next idiot you meet that asteroids and meteors have nothing to do with it.