The World

The Ringed Planet is a terrestrial globe surrounded by a ring of large rocks orbiting around it. The atmosphere of the planet extends beyond the planet ring provides a habitable space on said ring.
Because the radius of the atmosphere is so big the pressure is lower on the ring than the planet itself. The optimal conditions on the ring allowed the ecosystem to evolve easier on the orbiting rocks. The planet itself covered by the shadow cast by the ring is much harsher for the life.