7th Class Science Winds, Storm and Cyclones Atmosphere


Category : 7th Class

*     Atmosphere


Atmosphere of the Earth is best described by the temperature and presence of percentage of gases in air. Atmosphere protects living organisms form harmful ultraviolet radiation from the Sun. Temperature on the surface of the Earth is also influenced by atmosphere. Atmosphere of the earth is layered, which is divided into five main layers according to the height or altitude, and on increasing and decreasing temperature. The layers of atmosphere of the earth are, troposphere, stratosphere, mesosphere, thermosphere and exosphere. The first layer from the surface of the earth is troposphere. Troposphere is heated by the reflected sun rays of  the earth surface. It is spread about 8 km above the surface from pole and 18km above form the equator. The interface between troposphere and stratosphere is called Tropopause.

The layer above the tropopause is stratosphere. It is about 50 km from the tropopause. Ozone layer is within the layer of stratosphere. The thickness of the ozone layer is about 15 to 35 km, which varies according to the season.

Atmospheric pressure in the stratosphere layer is negligible. Temperature is increased as the altitude is increased. Stratopause is the boundary between stratosphere and mesosphere.

Mesosphere is extended up to 88 km from stratopause. In this layer most meteors burn up when they enter in the layer. In this layer, as the altitude increases, temperature decreases. Water vapor in this region is frozen into ice due to the extreme cold.

The layer above the mesopause is thermosphere. Temperature of the thermosphere is varied according to the solar activity. The region of the thermosphere is between 100 to 800 km.

The layer above the thermosphere is exosphere. A layer, which is known as ionosphere is between the thermosphere and exosphere. The ionosphere is ionized by solar radiation. Radio propagation on the Earth is due to the magnetosphere of ionosphere. Exosphere is the outer most layer of atmosphere

of the Earth. The exosphere is mainly consisting of hydrogen and helium gases. Density of the gases in this layer is very thin and particles are apart from each others. In this region solar wind is continuously flowing. Exosphere is extended up to about 10000 km.


Look at the following picture of layers of Earth's atmosphere






      The earth's atmosphere is layered according to the availability of gases, temperature and altitude. Which one of the following layers is found between the thermosphere and stratosphere?

(a) Troposphere

(b) Exosphere

(c) Mesosphere

(d) All of these

(e) None of these


Answer: (c)



      Tropopause is the boundary in the Earth atmosphere lies between in which one of the following layers?

(a) Between the thermosphere and exosphere

(b) Between the troposphere and stratosphere

(c) Between the stratosphere and mesosphere

(d) All of these

(e) None of these


Answer: (b)

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