Why is it the fact that ice floats vital to life on earth?

If ice did not float, then the ocean basins would fill up with ice that never thaws and this would at least disrupt if not completely prevent ocean currents from distributing heat around the planet and Earth would be too cold for living things over most of the planet. Earth would be locked in a permanent ICE AGE. Life may still exist in equatorial regions but we can'e assume it would have the range, complexity, or diversity it has now.