The earth does have life, but that doesn’t necessarily mean that other planets don’t. We just don’t have enough evidence to say one way or the other. Moons in the solar system may support bacterial life. We can detect organic molecules and other gases using telescopes. Jupiter’s moons are the best bet for supporting life, but we won’t find out until we get there. This page has a good summary for the best bets as sources of extra-terrestrial life: http://www.wired.com/wiredscience/2009/01/et-life/
We don’t know whether or not Earth is the only planet with life, other planets might actually have life too ! Earth just happens to have very good temperature for the growth of life because it’s the perfect distance from the sun !