Coal comes from the remains of trees, shrubs, and plants that grew millions of years ago, in tropical wetlands, such as those of the late Carboniferous period (the Pennsylvanian) at a time when the weather was mild and moist. The coal beds of today were once vast swamps.
When the plants and trees died, they fell into boggy water. They did not rot away completely. They changed into a slimy material called peat. Then the sea washed over the peat, bringing up sand and stones, and changing the soil around it. Over millions of years, water, weather and the continual movement of the soil compressed and dried this original peat into good coal. Also wood heated in an airless space can make charcoal.
Coal is a hard rock which can be burned as a solid fossil fuel. It is mostly carbon but also contains hydrogen, sulphur, oxygen and nitrogen. It is a sedimentary rock formed from peat, by the pressure of rocks laid down later on top. The harder forms of coal, such as anthracite, are metamorphic rocks, which mean they were changed by very high temperature and pressure.
It can be burned for energy or heat. About two-thirds of the coal mined today is burned in power stations to make electricity. Like oil, when coal is burned its carbon joins with oxygen in the air and makes a lot of carbon dioxide, which causes climate change. Because of that and other air pollution from coal most countries are turning to new sources of energy, such as solar power. But new coal power plants are still being built in some parts of the world, such as China.
