Natural resource of Class 9

The greenhouse effect refers to the change in the steady state temperature of a planet or moon by the presence of an atmosphere containing gas that absorbs and emits infrared radiation.Greenhouse gases, which include water vapor, carbon dioxide and methane, warm the atmosphere by efficiently absorbing thermal infrared radiation emitted by the earth’s surface, by the atmosphere itself, and by clouds. As a result of its warmth, the atmosphere also radiates thermal infrared in all directions, including downward to the Earth’s surface. Thus, greenhouse gases trap heat within the surface-troposphere system. The greenhouse effect is one of several factors that affect the temperature of the Earth.


Between 320 And 26 Km Above The Sea Level It Occurs Ozone Layer And The Part Of Atmosphere Containing It Is Called Ozonosphere (Stratosphere). This layer is established due to an equilibrium between phto-dissociaiation of ozone by UV-radiation and regeneration of ozone. The thickness of this ozonosphere averages 5km. the ozone layer acts as a shield and absorbs the harmful UV-radiations of the sunlight so protects the earth’s biota from the harmful effects of strong UV-radiations. So this layer is very important for the survival and existence of life n earth. 

Causes of Thinning of Ozone Layer :

The decline in spring-layer thickness is called ozone hole is largest over Antarctica and was just short of 27 million duringSpetember 2003.main chemicals responsible for destruction of ozone-layer are : chlorofluorocarbons(CFCs), halogens (used in fire extinguishers) methane and nitrous oxide. Out of these, most damaging is the effect of CFCs which are a group of synthetic chemicals and are used as coolants is refrigerators and air conditions; as cleaning solvents, propellants and sterilants etc. these CFCs produce “active chlorine” (CI and CIO radicals) in the presence of UV-radiations. These active chlorine radicals catalytically destroy ozone and convert it into oxygen.

Nitrous oxide : It is produced by industrial processes, forest fires, slid waste disposal, spraying of insecticides and pesticides, etc. methane and nitrous oxide also cause ozone destruction.

Effects of Ozone Depletion :

The thinning of ozone layer results in an increase in the UV radiation(in the range of 290-320nm) reaching the earth’s surface. It is estimated that a 5 per cent loss of ozone results in a 10 per cent increase in UV-radiations. These UV-radiations:

  • Increased incidences of cataract and skin cancer.
  • Decrease the functioning of immune system: due to killing of melanin- producing cells of the skin.
  • Inhibit photosynthesis in most of phytoplanktons so adversely affecting the food chains of aquatic ecosystems.
  • Damage nucleic of the living organisms.
  • Strip-cropping means the planting of crops in rows or strips to check flow of water.

Management of Natural Resources

Natural resources are in constant use and in fact, are being over used. Increase in human populations has a direct effect on the changes in the environment both physical and biological.

Physical changes in environment due to human activities are:

  • Building of roads, railways, houses and mining activities require the destruction of hills, levelling of mountains.
  • Deforestation for getting timber and wood for furniture and for more land for agriculture.
  • Development of villages, cities and factories.
  • Digging of drains, canals, lakes, irrigation tanks.
  • Building of dams for water storage, hydel power generation and agriculture. 
  • Conversion of marsh lands for human settlement.



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