CBSE Class 10 Answered

Petrol and coal are the fossil fuels. They are formed millions of years ago.

Formation of coal:

• Coal is formed from dead plants.
• Dead plants get buried deep in the Earth.
• The dead material gets converted into peat.
• Peat gets buried deeper.
• Under high pressure, the peat loses its moisture content and reduces in volume and gets converted into
• lignite which is a soft brown coal.
• As the lignite gets buried deeper in the Earth, due to high temperature and pressure, it becomes harder and convert into bituminous coal.
• Bituminous coals when further exposed to high temperature and pressure convert into anthracite coal, which is the highest rank coal with high carbon content.

Formation of petrol:

• The planktons, aquatic plants and animals when die get settled in the bottom of the sea.
• Soon they get covered by the mud.
• As more and more layers of mud settle, the lowermost layers of mud along with the dead material convert into a rock under high pressure and temperature.
• The dead, decaying material which gets trapped in the rock, loses its water content and changes into crude oil which is high in carbon.
• Since oil is denser than water, due to high pressure from below, it rises through the permeable rock.