Page 4 - 2.Lesson Notes-Water Harvesting, Coal and Petroleum

Advantages of water stored in the ground-
1. It does not evaporate.
2. It spreads out to recharge wells.
3. It provides moisture for vegetation over a wide area.
4. Does not provide breeding grounds for mosquitoes.
5. It doesn’t get contaminated by human or animal waste.

Coal and petroleum
 Coal and Petroleum both form fossil fuels and they require much time to get
replenished, so their judicious use is recommended in order to save them for
future generations.

Formation of Fossil Fuels
 Coal and petroleum were formed from the degradation of bio-mass millions of
years ago and hence these are resources that will be exhausted in the future
no matter how carefully we use them.
 Petroleum resources will last us for about forty years.
 Coal resources will last for another two hundred years.
 Since coal and petroleum have been formed from bio-mass, in addition to
carbon, these contain hydrogen, nitrogen and sulphur.
 When these are burnt, the products are carbon dioxide, water, oxides of
nitrogen and oxides of sulphur.
 When combustion takes place in insufficient air (oxygen), then carbon
monoxide is formed instead of carbon dioxide.
 Of these products, the oxides of sulphur and nitrogen and carbon monoxide are
poisonous at high concentrations and carbon dioxide is a greenhouse gas.
 Coal and petroleum are huge reservoirs of carbon and if all of this carbon is
converted to carbon dioxide, then the amount of carbon dioxide in the

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