Lilwrek, what the hell are you talking about there? Even from a religious point of view, it is impossible for extraterestrial life not to exist. It is just idiotic to be so vain as to think that the planet you are destroying is the only thing ever capable of sustaining life. Life is not limited to oxygen breathing creatures with body temperatures within our range of heat resistance, life is basically a desperate attempt of matter to sustain and preserv itself in a given environment, a balance gone wild. Because it is baance that determines matter to turn into energy and the other way around. Or at least in my view hehe.
Anyway, what was i talking about? Yea, look here: lants are aive too and they breathe CO2, not O2 like animal life. Plants and animals evolved in 2 different directions from the same basic life, which is capable of appearing in any place that has an exchange of matter and energy. Xenomorphs would probably be very confortable on a planet like Venus, there may already be life on Venus that we've never imagined, we can't know for sure since what we have on earth isn't fit for that atmosphere.
Anyway (again), i keep losing my line of thoughts, what i want to say, that i've said before is, the world is infinite. In infinity, everything is bound to exist. EVERYTHING. Eiter that, or the universe ends and there's nothing there, not even energy, not even nothing.