I agree. I mean, honestly, if this did happen, it obviously was not powerful enough to wipe out the ocean, or destroy our atmeosphere. Things like this don't come back. :T
The film claims it happened six times in history..why isn't humanity extinct then? Most importantly, how do we know it happened? We know that an asteroid wiped out the dinosaurs, but not all life. So..it's obvious it can't destroy all life on Earth.
If it happened 6 times, and we only go back to the dinosaurs, then, wouldn't it have destroyed humanity already?
Things like this don't seem real to me. This is why I never believe the Discovery Channel.