I was doing a project on meteors hitting earth and came across this site.
http://exitmundi.nl
It is a collection of end of the world Scenarios with a somewhat humorous slight put on it. Some of them are not realistic. They do even disprove a few commen myths, and provide counter points to alot of theie own scenarios. But for the most part, it serves to freak the hell out of you about how fragile life on earth really is.
Check it out if you'd like.