To start, the laws of physics are universal, so it follows that the laws of life are too. this discounts mistys idea of a 'non carbon' based life for.
so, to discuss if life can exist off earth, and considering the laws of life are universal, we only need to look at the only known examples here on earth, to work out what parameters need to be met. More on this in a moment.
now, either god clicked his fingers and life appeared on earth, or there art two possibilities.
One, is that life started by accident. in pools of amino acids, molecules randomly bumped into each other for millions (billions?) of years, until, the correct combination of molecules collided. lucky break! in fact, this is the favoured theory (outside of creationism).
the second, is that life could have travelled here from somewhere else. Perhaps inside a comet, meteor etc. if this was the case, then there is every chance life has been distributed elsewhere.
But back to the possibility of life living elsewhere. it is true, that we are extremely fortunate to be in a place where every factor necessary for life exists. It is often said that the probability of these conditions being met elsewhere are so slim. And this is true, however, most weeks someone wins the lottery. so not impossible. The main condition is water is needed. Now, space is packed with water. just the frozen stuff. So what you need is a place that has the right temperature to allow liquid water to exist. In our own solar system, there seems to be two possibilities. One is mars, and yes i know they have looked there for decades now with no luck. However, photos clearly indicate erosion patterns similar to that of which rivers would make on earth. So it is possible, that once life did exist, or perhaps still does well below the surface.
The other possibility within our solar system is on a moon. One of Jupiter's moons (i think). Now, we all know that jupiter is too far from the sun and thus this moon is covered in 15kms of ice. However, this is no ordinary moon. In-fact, its orbit is elliptical, not circular. The result of this, is that the moon itself changes shape, depending on its position in orbit. The moon is spherical at its farthest point to jupiter, and as it approaches jupiter, the enormous gravitational field (from jupiter) actually elongates the moon. So what hey? well, this may actually (well defiantly) crates an enormous amount of friction. perhaps enough, to allow for the ice to melt, some 15 kms below the surface. if this is the case, then life could exist there. No, it wont be any sophisticated alien, but more likely some type of single-cellular organism, blissfully unaware of anything. Would live in darkness, and perhaps generate some of its own light (like our little angler fish?)
Now, if in our tiny insignificant solar system, there is one planet that sustains life, and two other suspected locations that could contain life, it is completely plausible that the universe could have other environments that are similar to ours. If you deny this, you probably have not really contemplated the scale of the universe.
As for the comment above about the big bang being rubbish, its actually simple maths to calculate that all objects in the universe are moving away from the same point. all you need to do is track a few objects (and there are plenty to choose from) and its not hard to follow their trajectories to determine that started at the same point. a little more plausible than god snapped his fingers. I must also stress, to the religious types, that the big bang theory and evolution, are not heresies against the catholic church, so im guessing most Christian faiths are the same. I know once upon a time they would have been, but the catholic church has evolved. it once excommunicated Galileo for preaching the earth was spherical.
