The Anthropic Principal - Cosmology

There is a third explanation for the apparent friendliness to life:Life has been slowly fitted to what conditions prevail on the planet.This has it the other way around. Our planet is NOT particularly friendly to ANY life. The life on it has put up with the conditions that the planet does offer and has been slowly modified until it does very well with those conditions.Whatever the conditions (within a reasonable wide range) the life on it would find it "friendly". Tube worms in the deep sea hot vents find nearly boiling water "friendly". Some bacteria find the conditions under a few kilometers of rock "friendly". Other life forms find the antarctic "friendly". This is a pretty wide range of "friendly" and it may well be that there is life that can find even wilder enviroments "friendly".It isn't because these environments are so darned nice; it is because life has been tuned to get along in them.

Well it is just that "duhh". It hints that the question is a bit stupid. We wouldn't be asking it if life couldn't find a "friendly" niche on this planet. It is just that simple.In fact, the current biosphere is permiated with a nasty poison. The original life on the planet has had to retreat from most of it. It is almost totally unfriendly to that original life.However, after the biosphere was poisoned other life gradually tuned to find oxygen "friendly".