[Centurion2000]

However, if the surface ice were very thick, this would cut the water below off from oxygen and sunlight which are important for most forms of life on Earth, and so might have prevented life from developing.

That's a load of horsecrap. The first life developed under anaerobic conditions and would actually have died in an oxy/nitro atmosphere.

[RightWhale]

Point is good.

[Virginia-American]

However, if the surface ice were very thick, this would cut the water below off from oxygen and sunlight which are important for most forms of life on Earth, and so might have prevented life from developing.

That's a load of horsecrap. The first life developed under anaerobic conditions and would actually have died in an oxy/nitro atmosphere

Good point. Also, sunlight is not be necessary. There is a lot of tidal heating of the Jovian moons, so there may well be things similar to undersea vents there. Undersea vents on the Earth support life without sunlight.