The atmosphere is a thin layer of air that protects the Earth's surface from extreme temperatures. It has four layers: the troposphere, stratosphere, mesosphere, and thermosphere. It is a mixture of solids, liquids, and gases.
The early atmosphere was different than it is today. Volcanoes produced nitrogen and carbon dioxide, but little oxygen. Early organisms began producing oxygen over two billion years ago. Eventually, the oxygen formed an ozone layer that protects the Earth from harmful rays.
The gases in the atmosphere are 78% Nitrogen, 21% Oxygen, .04% water vapor, .037% Carbon Dioxide, and .93% Argon. Each gas has a different purpose, and there are also traces of neon, helium, methane, krypton, xenon, hydrogen, and ozone.
The atmosphere is changing because of pollution. Pollutants mix with oxygen and other chemicals and form smog. There are solids such as dust, salt, and pollen; and there are liquids which include water droplets and droplets from volcanoes.
The troposphere is the lowest layer. It extends up to 10 kilometers, and it contains 99% of the water vapor and 75% of the atmospheric gases. It is the first layer above the surface, and it contains most of the clouds and half of the Earth's atmosphere. Weather occurs in the troposphere. Most of the layer's heat is from the Earth, and temperature cools about 6.5 degrees C per kilometer of altitude.
The next layer is the stratosphere which is from 10 kilometers to 25 kilometers above the Earth's surface. A portion of this layer contains the ozone layer, which absorbs harmful rays from the sun. Th ozone layer is necessary for life! However, pollutants called CFC's are destroying the ozone. Planes fly in the stratosphere because it is very stable.
The next layer is the mesophere; it goes to 85 kilometers above the surface. It is the coldest layer and contains little ozone. Meteors or rock fragments burn up here. The ionosphere, a layer of charged particles, is in this layer.
The thermosphere is the thickest layer; it goes from 85 to 500 kilometers above the surface. It has auroras and is known for high temperatures. It warms as it filters out X-Rays and gamma rays from the sun. The ionosphere is here as well; it helps carry out radio waves.
Next is the exosphere, which merges into space. This is the upper limit of our atmosphere. It is the outer layer where space shuttles orbit.
The sun's energy is either reflected or absorbed. Albedo is the fraction of solar radiation reflected back into space; it is harmless. Absorbtion is the fraction of solar radiation NOT reflected into space; this is greenhouse. The greenhouse effect is solar energy that is absorbed by the Earth's land, and water is changed to heat that moves/radiates back into the troposphere where gases absorb the heat.
The Urban Heat Island Effect occurs when a metropolitan area is warmer than the surrounding rural areas. UHI Effect is caused primarily by modification of land surfaces in developments that use materials that retain heat.
