Life Needs Energy
Hi Guys
While life needs fluids - either water or water/ammonia - it also needs rich sources of energy. Deep ocean communities use chemosynthesis but they also benefit from all the chemical processing that has happened higher up in the ocean, which is what makes the oxygen that the vent animals need.
I seriously doubt there would be sufficient energy from volcanism to supply oxygen for extraterrestrial animals. Europa might have an extra energy input from Jupiter's radiation belts but it's pretty piddling.
Adam