As noted in the link Jikx provided, all life requires nitrogen (and the atmospheric N2) the the main source of it (at least once "fixed"). But not all life requires free, atmospheric O2 to survive. Some species of microorganisms find it downright lethal. Many large organisms (like humans) have evolved a need for O2 because it is such a great terminal electron acceptor used in biochemical processes. But there are several other electron acceptors that are used by other organisms.