How does earths atmosphere make condtions on earth suitable for living things?

You have that the wrong way round, LIVING things have changed Earth's atmosphere to make it suitable for them.

When Earth first came into being, the atmosphere was NOT like it is now, it could not sustain the life that exists today. Over Geological time tiny bacterial organisms generated the Oxygen that we have in our air today, and altered the whole environment of the planed in doing so.

Thus the driving factor is LIFE not the atmosphere.