The Quest for Coal

Digging DeeperHow Trees Become CoalPrevious

Millions of years ago much of the world was covered in swamps and forests. Trees and plants fell to the ground and sank into the mud, making a thick layer. The plant material rotted to form peat. Over time the weight of the overlying rock layers pressed down on the peat, turning it into coal.

Soft brown coal is called lignite. After awhile, harder coal called bituminous coal forms. Further heat and pressure create anthracite coal and graphite (metamorphic rocks). Graphite is carbon but it is not coal. Graphite is what pencil leads are made of.