Introduction to the atmosphere
NOVA - The Atmosphere
The Water Cycle
The Structure of Water
About the Water Cycle
The Water Cycle
Water on the web
USGS Water Science for Schools
The Water Cyle
The Fresh Water Ecosystem
The Water Cycle
The earth is surrounded by all kind of gases. This layer is called the earth's Atmosphere. Without this atmosphere life on earth isn't possible. It gives us air, water, heat, and protects us against harmful rays of the sun and against meteorites.
This layer around the earth is a colorless, odorless, tasteless 'sea' of gases, water and fine dust. The atmosphere is made up of different layers with different qualities. It consists of 78 percent nitrogen, 21 percent oxygen, 0,93 percent argon, 0,03 percent carbon dioxide and 0,04 percent of other gases.
The Troposphere is the layer where the weather happens. Above this layer is the Stratosphere and in between them is the Ozone layer, that absorbs the sun's harmful ultraviolet rays. Above the Stratosphere is the Mesosphere, the Thermosphere including the Ionosphere - and the Exosphere. The atmosphere measures about 500 miles (700km).
Where does the Atmosphere consist of?
The atmosphere has at the upper side no clear boundary, because higher in the atmosphere, the layer becomes thinner and thinner. It constantly loses molecules of lighter gases such as helium and hydrogen. The further we get from the earth, the atmosphere is divided in thin layers, based on changes in the temperature.
The Troposphere is the lowest layer of the atmosphere and measures about 7 miles(12 km). It contains over 75 percent of all the atmosphere's gases and vast quantities of water and dust. As the sun heats the ground, it keeps this thick mixture churning. The weather is caused by these churnings of the mass. The troposphere is normally warmest at ground level and cools higher up where it reaches its upper boundary (the tropopause). The tropopause varies in height. At the equator it is at 11,2 miles(8 km) high, at 50 N and 50 S, 5,6 miles(9 km) and at the poles 3,7 miles(6 km) high.
The Stratosphere extends from the tropopause up to its boundary (the Stratopause), 31 miles(50 km) above the Earth's surface. In this layer there is 19 percent of the atmosphere's gases and it contains little water vapour. Compared to the troposphere it is calm in this layer. The movements of the gases are slow. Within the stratosphere is the ozone layer, a band of ozone gas, that absorbs harmful ultraviolet rays of the sun. The higher you get in the atmosphere, the warmer the air gets. The temperature rises from -76 ºF(-60 ºC) at the bottom to a maximum of about 5 ºF(10 ºC) at the stratopause.
The mesosphere is the next layer above the stratopause and extends to its upper boundary (the Mesopause), at 50 miles(80 km) above the ground. The gases in the mesosphere are too thin to absorb much of the sun's heat. Although the air is still thick enough to slow down meteorites hurtling into the atmosphere. They burn up, leaving fiery trails in the night sky. The temperatures in the mesosphere drop to -184 ºF(-120 ºC) at the mesopause.