The air surrounding the Earth is called the atmosphere. Air is an invisible mixture of gases that surrounds the Earth. The atmosphere has been dividing into different layers. The different atmospheric layers are:
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1. Troposphere:
It is the layer of atmosphere nearest to the earth’s surface. It extends to an altitude of 16 kilometers. It influences the Earth’s climate. It contains all the constituents of air. Winds, storms, clouds, rain and all weather changes take place here.
2. Stratosphere:
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Bulkof the atmosphere lies below this sphere. This extends up to an altitude of 80 km from Earth’s surface. No oxygen exists in it.
3. Ionosphere:
This lies up to an altitude of 800 km. It extends from about 80 km to 800 km above the Earth. Man-made satellites circle at about 600 km above the Earth’s surface.
4. Exosphere:
It extends beyond an altitude of 800 km from Earth.
Composition of Air:
Air is mixture of several gases such as nitrogen, oxygen, rare gases (inert gases), carbon dioxide and water vapor.
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The air that we breathe is called inspired air (or inhaled air). The air that we breathe out is called expired air (or exhaled air).
The expired air contains more of carbon dioxide, is warmer and moister than inspired air. During respiration, oxygen gas is taken in and carbon dioxide gas is given out.
In the presence of sunlight, plants are able to convert carbon dioxide and water into sugar for food. This process is called photosynthesis. During this process, oxygen is given out by plants. This oxygen goes into the air. Humans and animals breathe in oxygen and breathe out carbon dioxide. Plants also use oxygen but they produce more than they use. Thus, plants do the opposite of what animal do. The composition of air has remained nearly constant because plants and animals complement each other. Thus, plants and animals together stabilize the atmosphere.
Rain dissolves gases present in air only to a very small extent. The composition of air is not affected by rain. The amount of water vapor in air is called humidity. Air always contains water vapor. Water vapor is produced due to the evaporation of water from oceans, seas, rivers, lakes, ponds, and streams. This evaporation is caused by the heat of the sun. The amount of water vapor varies from place to place. It is different even at one place during day and night and also from day to day. The maximum amount of water vapor which air can hold varies as the temperature changes. Warm air can hold more water vapor than cold air.
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Air has a certain capacity to hold water vapor. If this capacity of air is exceeded, water vapor condenses into water droplets and forms dew or rain. If the temperature of air decreases, water droplets freeze and fall as mist or hail or snow. Thus the water is constantly being recycled.
Air contains tiny solid particles of dust. These particles can be seen dancing in the air when a beam of sunlight steams into your room. The dust particles reflect the light and make the beam visible.
Importance of Atmosphere:
- It contains oxygen which is required by plants and animals.
- It filters the sunlight and the heat and allows only a part of it to reach the Earth. If there were no atmosphere, the Earth would have been very hot and life would not be possible. It thus acts like a blanket, protecting the Earth. It also reflects back many harmful rays. It contains the ozone layer, which absorbs harmful ultraviolet radiations.
- The circulation of air results in different climatic zones. In different climatic zones, different types of plants and animals live.