Figure5.2 also shows Earth's overall water balance, or the volume of water that passes through each part of the cycle annually. The amount of water vapor in the air at any one time is just a tiny fraction of Earth's total water supply. But the absolute quantities that are cycled through the atmosphere over a one-year period are immense some 380,000 cubic kilometers-enough to cover Earth's entire surface to a depth of about meter (39 inches). Estimates show that over North America almost six times more water is carried by moving currents of air than is transported by a the continents’ rivers