Just finished watching Hawking's documentary on aliens, made me want to talk about the possibility of alien life, specifically:
Do aliens exist? Based on our understanding of biochemistry, life needs cheimicals for reactions, a solvent for chemical reactions to occur (liquid), and energy (sun, heat, perhaps even radiation). It think this bodes well for life in the universe, and even in our own solar system. Concerning a liquid solvent, Earth and Mars are capable of liquid water near their surface, and outer moons are capable of liquid water under their surface, as well as other liquid states such as methane and nitrogen.
How would aliens react with humans? I'd imagine that advanced aliens would treat us much in the same way we treat inferior life forms. Nobody cares when they step on an anthill or kill a few bacteria, so why would an intergalatic civilization care about whipping us out if they wanted Earth's resources?