Peat forms when plant material, usually in marshy areas, is inhibited from decaying fully by acidic and anaerobic conditions. It is composed mainly of marshland vegetation: trees, grasses, fungi, as well as other types of organic remains, such as insects, and animal remains. Under certain conditions, the decomposition of the latter (in the absence of oxygen) is inhibited, and archaeologists often take advantage of this.
Peat layer growth and the degree of decomposition (or humification, transformation to humus) depends principally on its composition and on the degree of waterlogging. Peat formed in very wet conditions accumulates considerably faster, and is less decomposed, than that in drier places. This allows climatologists to use peat as an indicator of climatic change. The composition of peat can also be used to reconstruct ancient ecologies by examining the types and quantities of its organic constituents.
Under the proper conditions, peat is the earliest stage in the formation of coal.
Most modern peat bogs formed in high latitudes after the retreat of the glaciers at the end of the last ice age some 9,000 years ago. They usually grow slowly, at the rate of about a millimetre per year.
The peat in the worlds peatlands has been forming for 360 million years and contains 550 Gt of carbo

Peat exploitation in East Frisia, Germany

A peat stack in Ness in the Isle of Lewis (Scotland).

Worked bank in blanket bog, near Ulsta, Yell, Shetland Islands

Falkland Islanders shovelling peat in the 1950s

Peat is important for farmers and gardeners, who mix it into soil to improve its structure and to increase acidity. The most important property of peat is retaining moisture in soil when it is dry and yet preventing the excess of water from killing roots when it is wet. Peat can store nutrients although it is not fertile itself.
Peat is discouraged as a soil amendment by the Royal Botanic Gardens, Kew, England, and has been since 200
Peat is an important raw material in horticulture. However it is recommended to treat peat thermally, e.g. through soil
steaming, in order to kill inherent pest and reactivate nutrients.
Peat is soft and easily compressed. Under pressure, water in the peat is forced out. Upon drying, peat can be used as a fuel. It has industrial importance as a fuel in some countries, such as Ireland and Finland, where it is harvested on an industrial scale. In many countries, including Ireland and Scotland, where trees are often scarce, peat is traditionally used for cooking and domestic heating. Stacks of drying peat dug from the bogs can still be seen in some rural areas.
Peats insulating properties make it of use to industry.
Peat fires are used to dry malted barley for use in Scotch whisky distillation. This gives Scotch whisky its distinctive smoky flavour, often called "peatiness".
Although peat has many uses for humans, it also presents severe problems at times. When dry, it can be a major fire hazard, as peat fires can burn almost indefinitely (or at least until the fuel is exhausted). Peat fires can even burn underground, reigniting after the winter, provided there is a source of oxygen. Peat deposits also pose major difficulties to builders of structures, roads, and railways, as they are highly compressible under even small loads. When the West Highland Line was built across Rannoch Moor in western Scotland, its builders had to float the tracks on a mattress of tree roots, brushwood and thousands of tons of earth and ashes.
Peat bogs had considerable ritual significance to Bronze Age and Iron Age peoples, who considered them to be home to (or at least associated with) nature gods or spirits. The bodies of the victims of ritual sacrifices have been found in a number of locations in England, Ireland, and especially northern Germany and Denmark, almost perfectly preserved by the tanning properties of the acidic water. (See Tollund Man for one of the most famous examples of a bog body).
Peat wetlands formerly had a degree of metallurgical importance as well. During the Dark Ages, peat bogs were the primary source of bog iron, used to create the swords and armour of the Vikin