Atmosphere

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An atmosphere is a layer of gases surrounding a planet that is held in place by its gravity. An atmosphere is more likely to retained if the gravity is high and the atmosphere's temperature is low.

Atmosphere of Earth
The atmosphere of Earth protects life on Earth by absorbing ultraviolet radiation, and warming the surface with heat. It consists of 78 percent nitrogen, 21 percent oxygen, and the remaining one percent is a mixture of argon, vapor, carbon dioxide, and other small gases.

Layers
Troposphere: The troposphere is the lowest layer in the atmosphere and is about 7 miles (11 kilometers) thick. It is the layer where life life is, and where water exists. Most of the Earth's clouds and weather are found in here.

Stratosphere: The stratosphere is the second-lowest layer in the atmosphere and located between 7 to 30 miles (11 to 48 kilometers). Most airplanes, especially Boeings, travel in this layer. However, the air in this layer is too thin to breath.

Mesosphere: The mesosphere is in the middle of all the atmosphere's layers. It extends from 31 to 53 miles (50 to 85 kilometers). The air becomes slighty thicker in this layer, thick enough to stop meteors from reach the ground, burning them into ash.

Thermosphere: The thermosphere is the atmosphere's second-highest layer between 53 to 375 miles (85 to 600 kilometers). Most Space Shuttles can be found in this layer. This is also the hottest layer, at 2,000 degrees Celsius (3,600 degrees Fahrenheit).

Exosphere: At 6,200 miles (10,000 kilometers), the exosphere is the atmosphere's highest layer. In this layer, atoms and molecules escape into space and satelites orbit

the Earth, including the Hubble Space Telescope.