The atmosphere may be divided into different layers depending their distance from the Earth’s surface. There is no marked between the layers.
The troposphere is the lowermost as well as the densest layer of the atmosphere. It extends up to a height of 10-15 km. About three-fourth of the total atmosphere is contained in this layer which is thicker at the Equator (18 km) and thinner at the Poles (8 km). This layer contains most of the Water vapor and dust particles, which is why all weather changes takes place here. As dense air absorbs more heat, there is a decrease in temperature with an increase in height. Troposphere (‘tropo’ means change) has great importance for us.
The stratosphere is the layer above the troposphere and it extends to about 50 km above the Earth’s surface. This layer has no weather changes and is thus ideal for flying jet planes. The lower part of this layer is called the ozonosphere because of the concentration of ozone gas here. Ozone absorbs the ultraviolet rays of the sun, which are harmful to us. Since it absorbs ultraviolet rays this layer is extremely hot. Meteors entering the Earth’s atmosphere rarely go beyond the ozonosphere to hit the Earth’s surface as they burn up in this layer.
The mesosphere is the layer above the stratosphere. It extends to about 80 km above the Earth’s surface. Here the temperature decreases with an increase in height and falls as low as-90’ C. This belt has the coldest temperatures within the atmosphere.
The thermosphere lies beyond the mesosphere and extends to a height of about 450 km above the Earth’s surface. Here the Temperature quickly increases with height and reaches 1480’ C. The tremendous heat in this layer causes the gas molecules to break up into ions. These electrically charged ions reflect back radio waves towards the Earth. This layer, also called the ionosphere, is important for long distance communication.
The exosphere is the outermost layer of the atmosphere, extending beyond the thermosphere. Here temperatures are externally high and only a small amount of gases is found. The decrease in the gravitational pull allows the gas molecules to easily escape into space.
Importance of the Atmosphere:
The atmosphere is a huge protective layer around the Earth. Its different layers are like a filter, keeping the sun’s harmful radiations from reaching the surface of the Earth. It allows only a part of the sun’s heat to reach us, thus preventing the Earth from getting too hot. The amount of solar radiation received by the Earth is called insolation.
The carbon dioxide and water vapor present in the lower layers of the atmosphere absorbs the heat given off by the Earth’s surface. This prevents the Earth from getting cooled too quickly at night. Without the atmospheric layer, temperatures on Earth would be like that on the moon- Extremely cold during the night and extremely hot during the day.
The differential heating of the Earth’s atmosphere results in the weather phenomena and all life forms are affected by them.