In a pretty amazing story, BBC News reports that the "First oxygen-free animals found". Deep in the Mediterranean Sea, 3 species of Loricifera have been found. The scientists verified that eggs from them could hatch in an oxygen-free environment.
This is pretty amazing, and it shows that life is often possible where we would have imagined it to be impossible. HWA seemed to believe that the universe, not just the earth, was originally created to be inhabited.
So, if animals can hatch and live without oxygen, and if the theory of evolution were true, then you would think life would be common even in our own solar system instead of just on one planet.