Question

Short Answer Type Question
Give an account of atmosphere.

Answer 1

Hint: Earth is the only planet which provides suitable conditions making life possible on its surface. This is the result of the presence of a layer which surrounds our earth. On one hand, this layer maintains the temperature of the earth and on other hand, it protects us from outer harmful rays.

Complete Answer:
Meaning of Atmosphere: The atmosphere is a mixture of gases surrounding the Earth which is held by gravity. It filters the insolation and prevents the ultraviolet rays from reaching the Earth’s surface. It has water vapour, which helps in precipitation and formation of the hydrological cycle.

Composition of Atmosphere:
The atmosphere is composed of gases, water vapour and particulates. The most abundant gases are nitrogen(78 percent) and oxygen( 21 percent). Many other gases like argon, neon, helium, carbon dioxide are also present but in much lower amounts. 99 percent of the gases are confined up to a height of 30 kilometres.

Structure of the Atmosphere:
1. Troposphere: It is the lowermost layer of the atmosphere. Almost all of the phenomenons related to weather occur in this layer. Its height extends roughly to 8 kilometres near the poles and about 18 kilometres at the equator. Temperature decreases with increasing height at the rate of 6.5 degrees celsius per 1000 metres which is known as the normal lapse rate.

2. Stratosphere: It extends upto a height of 50 kilometres above the troposphere. It has the maximum concentration of ozone in its lower portion which is known as ozonosphere. This layer absorbs harmful ultraviolet radiations. As a result, the temperature rises in this layer.

3. Mesosphere: It extends upto a height of about 80 kilometres. It is the coldest layer of the atmosphere. Its upper limit is marked by mesopause.

4. Thermosphere: It occurs above 80 kilometres wherein temperature increases with increasing height due to the absorption of ultraviolet solar radiations. The most significant aspect of the thermosphere is the presence of the ionosphere(80km to 640km) in it.

5. Exosphere: It is the uppermost layer which extends beyond the mesosphere. In this layer, electrically charged particles are found abundantly.

Note: - The Northern Lights are the result of intense collisions between the atmosphere of the Earth and the Sun's rays. These are also known as aurora borealis. They're caused by electrically charged electrons from the solar wind colliding with particles in the Earth's atmosphere, visible as pulsing and rippling green curtains.
- Clouds present in the mesosphere are known as noctilucent clouds. As they are formed by ice crystals, these clouds shine in the night thus also known as night-shining clouds.