Substaining Life

The idea of people moving to Mars or the moon seems almost impossible. I know that the same thing was probaly said about talking across the seas or space travel. It seems like Hawkings does not want to say never, just along time from now. How long, well I believe that will be decided as the need increases for us to provide more housing than the earthcan hold. Like Hawking says it will be easier to go underground first, then look to the skies.