What is Atmosphere? Composition and Structure of Atmosphere - Class 7

Our earth is surrounded by a huge blanket of air called the atmosphere. All living beings on this earth depend on the atmosphere for their survival. It provides us the air we breathe and protects us from the harmful effects of the sun's rays. Without this blanket of protection, we would be baked alive by the heat of the sun during the day and get frozen during the night. So it is this mass of air that has made the temperature on the earth liveable.

Composition of the atmosphere

Air consists of a mixture of gases. Approximately 78% nitrogen, 21% oxygen, and 1% many other gases like carbon dioxide, Argon, Methane, Ozone, and water vapor in small quantities.

Structure of the atmosphere

Our atmosphere is divided into five layers starting from the earth's surface. These are the troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere

Troposphere:

This layer is the most important layer of the atmosphere. Its average height is 13 km. The air we breathe exists here. Almost all the weather phenomena like rainfall, fog, and hailstorms occur in this layer.

Stratosphere:

Above the troposphere lies the stratosphere. It extends up to a height of 50 km. This layer is almost free from clouds and associated weather phenomena, making conditions most ideal for flying airplanes.

One important feature of the stratosphere is that it contains a layer of ozone gas. We have just learned how it protects us from the harmful effect of the sun's rays.

Exosphere: The uppermost layer of the atmosphere is known as the exosphere. This layer has very thin air. Light gases like helium and hydrogen float into space from here.

Mesosphere: This is the third layer of the atmosphere. It lies above the stratosphere. It extends up to the height of 80 km. Meteorites burn up in this layer on entering from space.

Thermosphere: In the thermosphere, the temperature rises very rapidly with increasing height. The ionosphere is a part of this layer. It extends between 80 and 400 km. This layer helps in radio transmission. In fact, radio waves transmitted from the earth are reflected back to the earth by this layer.

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