Composition And Structure Of Atmosphere Class 11 Notes Geography Chapter 7 - CBSE

Chapter : 7

What Are Composition And Structure Of Atmosphere ?

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For all living things to survive, air is necessary.
The atmosphere, a concoction of several gases, surrounds the earth on all sides. It has gases that are essential for life, such as carbon dioxide for plants and oxygen for people and other creatures.
The air is a vital component of the Earth's mass, and 99% of the atmosphere's total mass is contained within a 32 km radius above the surface. The air is colourless and odourless, and it can only be felt when it blows as wind.
There are gases, water vapour, and dust particles in the atmosphere.
At a height of 120 km, oxygen will be essentially nonexistent due to a change in gas proportions in the upper layers of the atmosphere.
Up to only 90 km from the earth's surface you can find carbon dioxide and water vapour.
Carbon dioxide is a crucial gas for meteorology because it is transparent to solar radiation but opaque to radiation leaving the earth.
The amount of other gases is stable, but carbon dioxide has been increasing over the past few decades mostly due to the combustion of fossil fuels, which is substantially to blame for the greenhouse effect.
Ozone, another significant element of the atmosphere, is located between 10 and 50 km above the surface of the earth. It serves as a filter, absorbs ultraviolet rays from the sun, and blocks these rays from reaching the earth's surface.
Another changeable gas in the atmosphere is water vapour.
With altitude, water vapour gets smaller. It may make up 4% of the air in the humid and warm tropics, whereas
in the chilly and dry desert and polar regions, it may make up less than 1% of the air. Water vapour also contributes to the stability and instability in the air, acting as a blanket to prevent the earth from getting too hot or too cold.
The ability of the atmosphere to hold small solid particles, such as dust and salt particles, which act as hygroscopic nuclei around which water vapour condenses to produce clouds, from different sources, such as sea salts, fine soil, smoke – soot, ash, pollen, and broken-up meteoric fragments, is one of the reasons why the atmosphere is both stable and unstable. The atmosphere is made up of various layers with differing densities and temperatures. The earth's density is highest close to the surface and gets progressively less dense with altitude.
The troposphere is the lowermost layer of the atmosphere. Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator.
The zone separating the tropsophere from stratosphere is known as the tropopause. The air temperature at the
tropopause is about minus 800°C over the equator and about minus 45°C over the poles.
The stratosphere is found above the tropopause and extends up to a height of 50 km. One important feature of the stratosphere is that it contains the ozone layer. This layer absorbs ultraviolet radiation and shields life on the earth from intense, harmful form of energy.
The mesosphere lies above the stratosphere, which extends up to a height of 80 km. In this layer, once again, temperature starts decreasing with the increase in altitude and reaches up to minus 100°C at the height of 80 km.
The ionosphere is located between 80 and 400 km above the mesopause. It contains electrically charged particles known as ions, and hence, it is known as ionosphere.
The uppermost layer of the atmosphere above the ionosphere is known as the exosphere. This is the highest layer but very little is known about it.
The main elements of atmosphere which are subject to change and which influence human life on earth are temperature, pressure, winds, humidity, clouds, and precipitation.