(a) What are fossil fuels? Name three fossil fuels.
(b) Describe how, fossil fuels were formed.

(a) The exhaustible natural resources which are formed from the dead remains of living organisms or fossils are known as fossil fuels. The resources are present in limited amount in nature and are known as exhaustible natural resources.

For example, coal, petroleum and natural gas are fossil fuels.

(b) The fossil fuel such as coal is formed from the remains of dead vegetation. Earth had dense forests in low lying wetland areas about 300 million years ago. Due to natural processes, like flooding, these forests got buried under the soil. Due to soil deposition over these dead plants, they were compressed. The temperature also increased as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal. As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation.

The fossil fuel such as petroleum is formed from the dead animals under the sea. As these organisms died, their bodies settled at the bottom of the sea. They got covered with layers of sand and clay. Over millions of years, in the absence of air, with high temperature and high pressure, these the dead organisms were transformed into petroleum and natural gas.