Water is the only substance known to man whose solid state has a lower density than the liquid (all other environmental conditions being equivalent).

When a liquid of another substance, such as ethyl alcohol, freezes, the solid falls due to the action of gravity. Heat energy loss from the upper surface (by the process of convection due to differential densities between regions of differing temperatures) is therefore a rapid process and the liquid turns to solid very rapidly. Any creature which can exist in the alcohol (students, for example) will be left floundering on the surface to die in very short order.

When water freezes, the rising solid ice forms a skin which slows down this loss of heat energy considerably. Living creatures can survive under ice for considerable time as a result (and assuming they can access the dissolved oxygen in the water).

This is the reason life on this planet has survived ice ages. NASA has finally recognised the fact, after the scientific community has been pointing it out for a generation, and shifted its search for life on other planets to those which have water in evidence.