The most common atomospheric gas is

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The atmosphere refers to the layer of gases surrounding Earth.

The composition of the atmosphere contains the following gases. Nitrogen makes up 78 percent of the atmosphere which is its largest component. Next is oxygen which comprises 21 percent. The last 1 percent can be subdivided into the following gases-argon, carbon dioxide, neon and helium.

The atmosphere is very important because its layers each have significant features that help the Earth in various ways. The troposphere-layer nearest the Earth's surface is where weather events occur as well as winds. The stratosphere contains the ozone layer which protects Earth from harmful high-- energy radiation. The mesosphere has temperatures that decrease to the lowest in the atmosphere and the thermosphere has very hot temperatures nearly 1000 degrees C. Finally, there is the exosphere, the outermost layer which extends into outer space.

It is interesting to note that although carbon dioxide is a fraction of 1 percent of the atmosphere, it plays a role in keeping the planet warm and in recent years, the slight increase of carbon dioxide has led to global warming. It is also interesting to note that oxygen, which aerobic organisms depend on, is not the largest component of the atmosphere.

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