Atmosphere
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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.
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[edit] Temperature and the atmospheric layers
The temperature(how hot or cold it is) of the Earth's atmosphere changes with altitude (height); the mathematical relationship between temperature and altitude varies between the different atmospheric layers:
- Troposphere - 0 - 7/17 km, temperature becomes less with height.
- Stratosphere - 7/17 - 50 km, temperature becomes more with height.
- Mesosphere - 50 - 80/85 km, temperature becomes less with height.
- Thermosphere - 80/85 - 640+ km, temperature becomes more with height.
The boundaries between these areas are named the tropopause, stratopause and mesopause.
The average temperature of the atmosphere at the surface of earth is 14 °C.
[edit] Pressure
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).
[edit] Density and mass
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.
