The atmosphere is described as the layer of gases that surround the Earth and are locked in, or trapped, by the Earth's gravitational pull. The layer of gases that surround the Earth consist of oxygen, carbon dioxide, nitrogen, argon and other insignificant amounts of gases. The majority of the gas is nitrogen, followed by oxygen and then a combination of all other trace gases. All of these gases that comprise the atmosphere are also referred to as simply just air.
The gases that surround the Earth have an important job: they protect various life forms on the planet by absorbing harmful rays from the sun, warming the Earth and regulating the temperature difference between night and day. The atmosphere also carries a small amount of water vapor, in the clouds, which is what helps continue the Earth's water cycle so that all life forms can survive.
Five layers comprise the atmosphere: the exosphere, thermosphere, mesosphere, stratosphere and troposphere. The pressure, density, mass and thickness can change depending upon certain aspects within the atmosphere. Factors such as rivers, lakes and the ocean are all prime examples that show how these aspects within the atmosphere can change, as well as temperature, smog and other air pollution.
The largest portion of water absorbed by the atmosphere comes from the ocean. The clouds absorb this precipitation and store it until they are so heavy, they cannot hold any more moisture. Depending upon the temperature, it may snow or rain. Typically, moisture is released in the form of water, or rain. It is only released as snow if the temperature in the sky reaches freezing or below freezing. The temperature on the ground will determine whether the snow sticks or melts. Approximately two-thirds of the precipitation absorbed by the atmosphere is returned back to the Earth.