http://en.wikipedia.org/wiki/Extinction_event http://en.wikipedia.org/wiki/Extinction_event http://www.skepticalscience.com/Earths-five-mass-extinction-events.

http://en.wikipedia.org/wiki/Extinction_event http://en.wikipedia.org/wiki/Extinction_event http://www.skepticalscience.com/Earths-five-mass-extinction-events.html http://www.skepticalscience.com/Earths-five-mass-extinction-... Then theorize on the older civilizations which we have little record outside of temples of engineering which can baffle the mind, and, perhaps, at the apex of planet-lift off, a Caldera blows. Just a thought.