<P> Water is a liquid at the temperatures and pressures that are most adequate for life . Specifically, at a standard pressure of 1 atm, water is a liquid between 0 ° C (32 ° F) and 100 ° C (212 ° F). Increasing the pressure slightly lowers the melting point, which is about − 5 ° C at 600 atm and − 22 ° C at 2100 atm . This effect is relevant, for example, to ice skating, to the buried lakes of Antarctica, and to the movement of glaciers . (At pressures higher than 2100 atm the melting point rapidly increases again, and ice takes several exotic forms that do not exist at lower pressures .) </P> <P> Increasing the pressure has a more dramatic effect on the boiling point, that is about 374 ° C at 220 atm . This effect is important in, among other things, deep - sea hydrothermal vents and geysers, pressure cooking, and steam engine design . At the top of Mount Everest, where the atmospheric pressure is about 0.34 atm, water boils at 68 ° C (154 ° F). </P> <P> At very low pressures (below about 0.006 atm), water cannot exist in the liquid state and passes directly from solid to gas by sublimation--a phenomenon exploited in the freeze drying of food . At very high pressures (above 221 atm), the liquid and gas states are no longer distinguishable, a state called supercritical steam . </P> <P> Water also differs from most liquids in that it becomes less dense as it freezes . The maximum density of water in its liquid form (at 1 atm) is 1,000 kg / m (62.43 lb / cu ft); that occurs at 3.98 ° C (39.16 ° F). The density of ice is 917 kg / m (57.25 lb / cu ft). Thus, water expands 9% in volume as it freezes, which accounts for the fact that ice floats on liquid water . </P>

When were the hydrogen atoms in water made