CBSE Class 9 Answered

Coal, petroleum and natural gas are all fossil fuels. They are fossil fuels because they were formed from plants and animals that decayed, and then pressure, bacteria, and heat preserved them in the earth's crust for millions of years. Eventually, these decayed plants and animals went through a chemical change and became fossil fuels, such as coal. Some of these fuels, like petroleum, were actually formed where salt water once covered the land. That's why we may see oil rigs in the ocean.