A log is part of a plant, and it burns.

Coal burns too, because coal was once plants.

A very long time ago, swamps covered big parts of the land, full of tall plants.

A swamp today, in Louisiana. The swamps that coal came from looked something like this.

When the plants died, they fell into the swamp water, and mud covered them before they could rot away.

More mud and sand piled on top, layer after layer, for a very long time.

The weight of the layers pressed the dead plants flat and hard, and they slowly turned black.

The pressed plants became coal.

Swamp plants, buried in mud, pressed for a very long time, became coal.

A black layer of coal between layers of gray rock, in a hillside.