I think that the way the universe is believed to have been created (big bang), has just brought into being a lot of unique objects which are relative to eachother, such as the temperature of planets close to, and distant from the sun, or even the size, shape and mass of different planets and stars.

I guess the earth just got lucky, it happened to contain the right ingredients to create life as we know it. From what I have read/seen so far, it isn't possible for this to happen on other planets due to certain gases, high/low/no gravity extreme temperatures both hot and cold etc.

If there is a galaxy that contains a planet with life on it, I don't think we will ever know about it in our life time.