The asteroid or comet impact widely implicated in the dinosaurs' demise would also have damaged plankton production in the oceans.

BBC: Ammonite diet revealed in X-rays

What about an asteroid or comet impact?

WSJ: The Panic Over Fukushima

Deep Impact has now set its sights on comet Ison during a 36-hour period in mid-January.

BBC: Comet Ison caught on film by Deep Impact craft

On July 4th, the spacecraft Deep Impact will launch a projectile at Tempel 1, a comet NASA has been watching for a few years.

NPR: NASA 'Deep Impact' Probe Targets Comet