On Earth there is a continuous cycle of water. Water moves from the oceans to air and land and then back to the oceans. This cycle is driven by the Sun’s energy as it heats the oceans and causes evaporation. This water vapor enters the Earth’s atmosphere. There is condenses back into a liquid as droplets. Once these droplets become heavy enough they fall back to Earth as either snow or rain. Water thus cycles between three different states of matter; liquid: as water, solid: as ice, and gas: as water vapor. The following processes are employed in this cycle.
- Evaporation – Heat from the sun evaporates water from bodies of water, such as oceans, rivers, lakes, and any open container. This vapor rises into the atmosphere and is then conveyed by the wind.
- Transpiration – As in evaporation, the sun creates heat which coverts water to vapor from the underside of leaves of plants. Plants obtain the water to grow from the soil by their roots.
- Condensation – As water vapor cools under certain conditions it forms small water droplets or ice crystals. This process is condensation. Condensation can occur on any cool surface such as a mirror (fogging) or the ground (frost /dew)
- Precipitation – When the water droplets in clouds merge together and become too heavy precipitation occurs. The droplets fall to earth as rain or if cooler as hail/snow.. During the cycle, water, at times, is stored in lakes, glaciers, underground, or in living organisms. Rivers and stream can move the water back to the oceans to complete the cycle. Or it can directly evaporate to the atmosphere.