NCERT Class 7 Geography Chapter 4: Air Completes Notes Part 1

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Air

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Composition of Atmoshere

Composition of Atmoshere

Now we will start with composition of Air. As we know most of the atmospheric air constitutes nitrogen then you have oxygen, 1% is nearly water vapor and then you have predominantly argon which is an inert gas and finally you have the carbon dioxide.

Now let’s understand about the importance of these gases into atmosphere.

  1. Nitrogen: Nitrogen is important for survival of many bacteria which use nitrogen for fixation.

  2. Oxygen: Oxygen is byproduct of the process of photosynthesis so under the process of photosynthesis plants take in carbon dioxide and release oxygen. This oxygen is released by the plant but used by human being to be inhale oxygen and this is important for survival.

  3. Carbon dioxide: Carbon dioxide is exhaled or what we remove out is carbon dioxide. This carbon dioxide that we exhale is used by plants for the process of photosynthesis to release free oxygen into the atmosphere.

Now again there other sources which release carbon dioxide into the atmosphere. For example, burning of fossil fuels, burning of fossil fuels release carbon dioxide into atmosphere. Cutting of trees or deforestation increases carbon dioxide concentration. All these process lead to increase in the greenhouse gases. It increases the amount of heat that is strapped in the atmosphere and therefore these gases are known as greenhouse gases. These greenhouse gases lead to increase in temperature of the globe and that is what is known as global warming. The impact of global warming could be seen as rise in sea level, this rise in sea level would increase in flooding activities which would increase coastal submergence. So these are some of the consequences that would be felt because of global warming. Now next is structure of atmosphere.

Structure of Atmosphere

  • Watch Video Lecture on YouTube: Layers of Atmosphere - 4 Layers in Thermal & 2 in Magneto-Electrical Structure

    Layers of Atmosphere - 4 Layers in Thermal & 2 in Magneto-Electrical Structure

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Image shows Structure of Atmosphere

Image Shows Structure of Atmosphere

Now when we classify the structure of atmosphere we start with the lowermost layer which is known as troposphere, troposphere on an average height is 13 km and has the active weather phenomenon that occurs, you have cloud formation, you have rainfall, fog, hail etc. so all those weather phenomena occur in troposphere layer. This layer usually extends up to 20 km but average height is considered is 13 km. Now next to troposphere comes the stratosphere. Stratosphere is the layer where you have most of the airplane that are flying and this belt is free of clouds and so free of weather phenomena. I could say it takes upto 50 km and this is stratosphere where you have Ozone layer, ozone layer is O3 with Oxygen is O2 and Ozone O3. This ozone protects us from the harmful ultraviolet rays that come on to the surface of the earth. Ozone is present in to stratosphere.

Now next is mesosphere, mesosphere extends up to 80 km, so extension of mesosphere lives up to 80 kilometres and it is in this mesosphere that you have most of the meteorites that are burnt up. Next to mesosphere you have thermosphere as you can see this line denotes the temperature change and in thermosphere you have rapid increase in the temperature. You have rapid rise of temperature as in the case of thermosphere. Thermosphere is known for ionosphere belt as a result you have maximum radio transmissions that occurs. And beyond thermosphere you have exosphere. And that exosphere extends to the outermost layers which mainly includes light gases like helium and hydrogen or move up to the outside atmosphere. Now next is weather Vs. Climate.

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