About 300 million years ago the earth had dense Forests in low lying wetland areas. Due to natural processes, like Floods, earthquakes, volcanoes, these forests got burried under the Earth’s surface. As more Soil deposited over them, they were compressed. The Temperature also rose as they sank deeper and deeper. Under high Pressure and high Temperature, dead plants got slowly converted into coal.

The above passage gives detail about the process of formation of coal. Before 300 million years, dense forests due to natural phenomenon like earthquakes, volcanic eruptions, floods etc. get buried under the surface of the earth. Soil gets deposits over them and they get compressed. As they are pressed more deep into earth’s surface the temperature increases. Due to high temperature and pressure, they slowly get converted into coal by carbonization process.