In ancient times, wood was the most common source of heat energy. The<br />
energy of flowing water and wind was also used for limited activities. Can

you think of some of these uses? The exploitation of coal as a source of

energy made the industrial revolution possible. Increasing

industrialisation has led to a better quality of life all over the world. It has

also caused the global demand for energy to grow at a tremendous rate.

The growing demand for energy was largely met by the fossil fuels – coal

and petroleum. Our technologies were also developed for using these

energy sources. But these fuels were formed over millions of years ago

and there are only limited reserves. The fossil fuels are non-renewable

sources of energy, so we need to conserve

them. If we were to continue consuming these

sources at such alarming rates, we would

soon run out of energy! In order to avoid this,

alternate sources of energy were explored.

But we continue to be largely dependent on

fossil fuels for most of our energy

requirements (Fig. 14.1).

Burning fossil fuels has other disadvantages too. We learnt in Class IX

about the air pollution caused by burning of coal or petroleum products.

The oxides of carbon, nitrogen and sulphur that are released on burning

fossil fuels are acidic oxides. These lead to acid rain which affects our

water and soil resources. In addition to the problem of air pollution,

recall the green-house effect of gases like carbon dioxide.