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) between the 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 What happens to precipitation once it has fallen on land? A portion of the water soaks into the ground(called infiltra tion), slowly moving downward, then laterally, finally seeping into lakes, streams, or directly into the ocean. When the rate of rainfall exceeds Earth's ability to absorb it, the surplus water flows over the surface into lakes and streams, a process called runoff. Much of the water that infiltrates or runs off eventually