I in no way believe that Earth is the only source of life in the universe, it's just too big for that. But that is not incogruous with my beleif and the teachings in the bible, because Jesus sent his disciples (sp?) to preach not to the Jews, but to the Gentiles, meaning everyone who was not a Jew. Does that limit them to just this Earth, I think not.
But the beauty of Islam is that you do not need to be concerned with other forms of life. We believe that you must understand Allah created us from Adam and Eve and he also created plants and animals that we must respect as his creation. Of course there are other wonders beyond Earth, that is merely the power of Allah. Even though there might be life on other planets, it wont affect us since only humans will be judged when the day of ressurection comes. Again animals and plants will not be judged.