Notes On Structure - CBSE Class 7 Geography
Our atmosphere is divided in to five different layers i.e. the Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.  The troposphere is the lowermost layer in the atmosphere and is the densest of all layers. The average height of troposphere is 13 kilomteres from the earth’s surface. This layer is responsible for the entire weather phenomenon like rainfall, fog and hailstorm. Stratosphere forms the next layer of the atmosphere and extends upwards from the troposphere up till a height of 50 kilometers. The words ‘Stratus’ means spreading out and layer provides suitable conditions for the supersonic jets, weather balloons and flying airplanes or commercial aircrafts. Stratosphere is less dense and clouds are almost absent. The most important feature of this layer is the presence of Ozone layer; stratosphere has the maximum concentration of the Ozone Layer. Ozone layer plays a vital role in regulating the earth’s temperature and absorbing the harmful ultraviolet radiations from the sun. Above the stratosphere lies the mesosphere layer. The height of mesosphere is 50-80 kilomteres above the earth’s surface and has the coldest temperatures in the atmosphere. Falling stars are nothing but meteorites that burn up in the mesosphere when entering the atmosphere. The fourth layer in the atmosphere above mesosphere is the thermosphere layer. The temperature here rises rapidly with increase in the altitude. However, the boundary between mesosphere and the thermosphere, known as mesopause, is the coldest place on the earth’s atmosphere having a temperature of minus 100 degrees centigrade. The international space station which orbits the earth, lies in the thermosphere layer. Above the thermosphere layer is the ionosphere which extends up to 80-400 kilometers from the earth’s surface. This layer reflects the radio waves enabling radio transmissions from one point to another on the earth. The exosphere is the uppermost layer of the earth’s atmosphere and extends up to 960-10,000 kilomteres above the earth’s surface. The main components of this layer gases like hydrogen and helium.

#### Summary

Our atmosphere is divided in to five different layers i.e. the Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.  The troposphere is the lowermost layer in the atmosphere and is the densest of all layers. The average height of troposphere is 13 kilomteres from the earth’s surface. This layer is responsible for the entire weather phenomenon like rainfall, fog and hailstorm. Stratosphere forms the next layer of the atmosphere and extends upwards from the troposphere up till a height of 50 kilometers. The words ‘Stratus’ means spreading out and layer provides suitable conditions for the supersonic jets, weather balloons and flying airplanes or commercial aircrafts. Stratosphere is less dense and clouds are almost absent. The most important feature of this layer is the presence of Ozone layer; stratosphere has the maximum concentration of the Ozone Layer. Ozone layer plays a vital role in regulating the earth’s temperature and absorbing the harmful ultraviolet radiations from the sun. Above the stratosphere lies the mesosphere layer. The height of mesosphere is 50-80 kilomteres above the earth’s surface and has the coldest temperatures in the atmosphere. Falling stars are nothing but meteorites that burn up in the mesosphere when entering the atmosphere. The fourth layer in the atmosphere above mesosphere is the thermosphere layer. The temperature here rises rapidly with increase in the altitude. However, the boundary between mesosphere and the thermosphere, known as mesopause, is the coldest place on the earth’s atmosphere having a temperature of minus 100 degrees centigrade. The international space station which orbits the earth, lies in the thermosphere layer. Above the thermosphere layer is the ionosphere which extends up to 80-400 kilometers from the earth’s surface. This layer reflects the radio waves enabling radio transmissions from one point to another on the earth. The exosphere is the uppermost layer of the earth’s atmosphere and extends up to 960-10,000 kilomteres above the earth’s surface. The main components of this layer gases like hydrogen and helium.

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