The hydrologic cycle is a gigantic worldwide system powered by energy from the Sun in which the atmosphere provides the and continents (Figure 5.2) water evaporates into the atmosphere from the ocean and to a much lesser extent from the continents. Winds transport this moisture laden air, often great distances, until conditions cause the mois- ture to condense into clouds and to precipitate and fall. The precipitation that falls into the ocean has completed its cycle and is ready to begin another. The water that falls on the continents, however, must make its way back to the ocean