Quote Originally Posted by a500lbgorilla
For Earth to support life, a lot of things had to go right. I think the chances that some random planet will support life is very slim. And the chances of that planet remaining inhabitable long enough for intelligent creatures to show up is even more slim. So if there is another planet supporting smart people, it's probably incredibly far away from us.
Drake equation:

http://en.wikipedia.org/wiki/Drake_equation