In addition to these vast bodies of surface water, atmospheric moisture is visible in the photograph in the form of clouds of water droplets. The atmospheres of the other terrestrial planets have very little water content, but water vapor is measurable on Venus and Mars. Water is constantly cycled between the atmosphere and surface of Earth. Most water vapor enters our atmosphere by evaporation from surface water and wet soil. Some water vapor also enters our atmosphere from the leaves of plants by a process called transpiration .
Water returns to the surface by condensation in the atmosphere and precipitation.
Clouds of water droplets form when water vapor condenses in the atmosphere. These water droplets may then precipitate to the surface in the form of rain or snow. You are all well aware, however, that clouds to do necessarily lead to precipitation. Evaporation removes heat energy from the source of the water. When the water vapor condenses in the atmosphere, the heat energy in the vapor is released.