There are two main explanations that have been offered for our planets peculiar friendliness to life.
The design theory says that God made the world, placed it in the Goldilocks zone not too hot and not too cold, but just right (too far from our sun means liquid water remains frozen and too close it boils) and deliberately set up all the details for our benefit.
Namely: liquid water, nearly circular life friendly orbit, sharing the solar system with the massive gravitational vacuum cleaner of Jupiter well placed to intercept small planet destroying asteroids, Earths single relatively large moon which serves to stabilize our axis of rotation, and helps to foster life in various other ways, and our unusual sun not being a binary, locked in mutual orbit with a companion star which would be too chaotically variable to sustain life.
The other is the anthropic principal or approach (philosophical consideration that observations of the physical Universe must be compatible with the conscious life that observes it). This is a very different view and has a Darwinian feel. The great majority of planets in the universe are not in the goldilocks zones of their respective stars, and not suitable for life. However small the minority of planets with just the right conditions for life may be, we necessarily have to be on one of that minority, because here we are thinking about it!
Source information Wikipedia / Richard Dawkins The God delusion
