The water cycle is the continuous movement of water from the atmosphere to the earth. The water that moves from the atmosphere to the earth is called precipitation. However, the water return to the atmosphere through evaporation.
During a rain storm, some of the rainwater evaporates as it falls to the ground. But most of the rainwater runs along the surface of the ground and travels to rivers, streams and ponds. The water running along theses surfaces are known as runoff water. Large amounts of precipitation also enter the soil to become ground water. The warm air that rises through the atmosphere contains tiny droplets of water. This water cools as it climbs higher into the atmosphere causing the water vapor to condense into droplets of water which form clouds. The droplets collect to form drops that eventually fall from the clouds as rain. If the water vapor condenses at a temperature below the freezing point of water then snow is formed.
Ground water is also a part of the water cycle. The ground holds and receives water from precipitation. However, some of the water moves downward into subsoil and fills the spaces around the rock particles. In the upper level of the soil, where it is saturated with water, the water will run off the surface instead of penetrating into the soil. The depth of the water table depends on the amount of precipitation, the nature of the rock layer under the soil, the proximity of large bodies of water, and the conditions of the soil receiving water.
Land organisms may pick up water at various points in this cycle. Most commonly, land animals get their water by drinking, and the plants by absorbing it from the soil. In all organisms some water becomes chemically incorporated into living substances, later to reappear when the substances are broken down. Furthermore, all organism contain water in which most of the living processes take place. Thus water is always involved both in the structure and in the activities of living things.
On land, both plants and animals lose water to the atmosphere: in plants, largely from the leaves; in animals through breathing or evaporation from the skin. Still more water is released when animals discharge wastes. Eventually all water taken in by organisms return to the atmosphere.
These are just a few of the cycles that exist within nature. I will now focus on two of the many environmental crises that exist on our planet- the greenhouse effect and acid rain. I will attempt to explain what these concepts are and state the problems that they are creating on our planet. I will also list some of the ways in which we can help in preventing these processes from destroying our planet.