Reference Terms
from Wikipedia, the free encyclopedia

Earth's atmosphere

Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity.

It contains roughly 78% nitrogen and 21% oxygen 0.97% argon and carbon dioxide 0.04% trace amounts of other gases, and water vapor.

This mixture of gases is commonly known as air.

The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

The atmosphere has no abrupt cut-off.

It slowly becomes thinner and fades away into space.

There is no definite boundary between the atmosphere and outer space.

Three-quarters of the atmosphere's mass is within 11 km of the planetary surface.

Note:   The above text is excerpted from the Wikipedia article "Earth's atmosphere", which has been released under the GNU Free Documentation License.
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