Millions of years ago, on parts of the Earth that were covered by glaciers, the thick ice dug into the Earth's surface, making holes that filled up with water and eventually turned into bogs. A bog is a kind of wetland that has wet, spongy, peaty soil.

How bogs form

Bogs begin to form as a lake or other body of water becomes covered with a floating mass of plants that keeps growing thicker. Pieces of these plants sink to the bottom of the water. The lake eventually fills up with plant matter coming down from the floating plants and up from the matter that settles at the bottom. When the vegetation is still floating, the bog is called a quaking bog. The surface of a quaking bog will sink or quake when a person or animal walks on it.

As the plant matter in bogs decomposes, or rots, it forms peat. The peat can be removed from the bog and dried and then burned as fuel.

Types of bogs

There are three main types of bogs. In cool regions, the typical kind of bog contains simple plants like mosses, notably sphagnum moss. This kind of bog is often called a sphagnum bog. A sphagnum bog also has heaths, which are shrubby plants that thrive in poorly drained soil. The second kind of bog is called a fen. It is very similar to a sphagnum bog but contains some groundwater. Minerals in the groundwater allow grassy plants such as reeds to grow in fens. The third kind is the tropical tree bog. The tropical tree bog is found in warm, tropical areas and contains mostly evergreen trees. There are few animals in any bogs.

Where bogs are found

Sphagnum bogs are found across very large areas of Russia, Canada, and Northern Europe. They also occur in wetter areas south of those regions, such as in Great Britain and Ireland. Fens often are found in the same areas as sphagnum bogs. Tropical tree bogs cover large areas in Malaysia, Indonesia, tropical South America, and Africa.