Atmosphere of Earth
||The English used in this article may not be easy for everybody to understand. (February 2012)|
Earth's atmosphere is the layer of gases around the planet Earth. The atmosphere is held in place by Earth's gravity. It is made up of nitrogen (78.1%) and oxygen (20.9%), with small amounts of argon (0.9%), carbon dioxide (~ 0.035%), water vapor, and other gases. The atmosphere protects life on Earth by absorbing (taking) ultraviolet radiation from the sun, and balancing the temperature on earth between day and night.
The atmosphere does not end at a specific place. It just gets thinner when you go higher. There is no clear line between the atmosphere and outer space. 75% of the atmosphere is within 11 km of the Earth's surface.
History of Earth's atmosphere [change]
Originally, the Earth's atmosphere had virtually no free oxygen. Its gradual change to the present state was a long process (see Great Oxygenation Event). which started with cyanobacteria. They were the first organisms to produce free oxygen by photosynthesis. Most organisms today need oxygen for their metabolism; only a few can use other sources for respiration.
Temperature and the atmospheric layers [change]
Some parts of the atmosphere are hot or cold, depending on height. If you were to climb straight up, it would get colder, then, it would get hotter, as you got higher. These changes of temperature are divided into layers. These are like layers of an onion. But you can not see any difference going from one layer to another layer. You can only feel the change in temperature; start getting hotter in the new layer, or start getting colder.
These are the layers of the atmosphere, starting from the ground:
- Troposphere - Starts at the ground. Ends somewhere between 7 to 14 kilometers. It gets colder as you get higher. This layer affects our daily life.
- Stratosphere - Starts at 7 to 14 kilometers. Ends at 50 km. It gets hotter as you get higher. There is little water vapor and other substances in this layer. Airplanes fly in this layer because it is usually stable.
- Mesosphere - Starts at 50 km. Ends at 80 or 85 km. It gets colder again as you get higher. Winds in this layer are strong, so the temperature is not stable.
- Thermosphere - Starts at 80 or 85 kilometers Ends at 640 km or higher. It gets hotter again as you get higher. This layer is very important in radio communication because it helps to reflect AM radio waves.
Where one layer changes to the next have been named "-pauses." So the tropopause is where the troposphere ends (7 to 14 kilometers high). The stratopause is at the end of the stratosphere. The mesopause is at the end of the mesosphere. These are called boundaries.
The average temperature of the atmosphere at the surface of earth is 14 °C.
The atmosphere has pressure. This is because, even though air is a gas, it has weight. The average pressure of the atmosphere at sea level is about 101.4 kilopascals (about 14.7 pounds per square inch).
Density and mass [change]
The density of air at sea level is about 1.2 kilograms per cubic meter. This density becomes less at higher altitudes at the same rate that pressure becomes less. The total mass of the atmosphere is about 5.1 × 1018 kg, which is only a very small part of the Earth's total mass.
- Heinrich D. Holland: The oxygenation of the atmosphere and oceans. In: Phil. Trans. R. Soc. B, vol. 361, 2006, p. 903–915 http://rstb.royalsocietypublishing.org/content/361/1470/903.full.pdf
- Knoll, Andrew H. 2004. Life on a young planet: the first three billion years of evolution on Earth. Princeton, N.J. ISBN 0-691-12029-3
Other websites [change]