Forget "Armageddon" and "Deep Impact" and "Meteor". Forget those bad made-for-TV movies on the subject.
What would happen if a serious asteroid hit the Earth?
Not those little itty-bitty ones the size of a car. BIG. BIG like in one of the serious asteroids that has been coming closer and closer to this planet.
Here's what it would look like. (Note: the Pink Floyd music was added by the poster.)
NOW... are you ready to put some serious thought into space colonization?