The amount of water that is on the earth at any time remains fairly constant because water moves from one reservoir to another, such as from a river to the ocean or from the ocean to 'atmosphere. This cycle involves the exchange of energy which causes a change in temperature. This is why when evaporation occurs, it takes energy from the surrounding environment and cools the environment. During condensation, energy is released and the surrounding environment becomes warmer. The atmosphere is a mixture of nitrogen, oxygen and other gases that surround the earth. The atmosphere is made up of five layers known as the troposphere, stratosphere, mesosphere, thermosphere and exosphere. The troposphere is the lowest layer of the Earth's atmosphere; it is also where all of the earth's weather conditions occur. The stratosphere is the second layer of the atmosphere, just above the troposphere. Above the stratosphere is the mesosphere and above is the troposphere. The highest region of Earth's atmosphere is the exosphere. The air in the exosphere is extremely thin and almost the same as space. One of the many reasons why Earth's atmosphere is important is because it freezes