Peat is found in wetland areas - bogs, moors, muskegs, pocosins, mires, and peat swamp forests and forms when plant material 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. Approximately 60% of the world's wetlands are peat. About 7% have been exploited for agriculture and forestry. Under proper conditions, peat will turn into lignite coal over geologic periods of time. It is harvested as an important source of fuel in certain parts of the world, notably in Ireland. By volume there are about 4 trillion m³ of peat in the world covering a total of around 2% of global land mass (about 3 million km²), containing about 8 billion terajoules of energy.
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.
The peat in the world's wetlands has been forming for 360 million years. 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.
Peat material is either fibric, hemic, or sapric. Fibric peats are the least decomposed, and comprise intact fibre. Hemic peats are somewhat decomposed, and sapric are the most decomposed. Phragmites peat is one composed of reed grass, (Phragmites Australis), along with other grasses. It is denser than many other types of peat. Engineers may describe a soil as 'peat' which has a relatively high percentage of organic material. This soil is problematic because it exhibits poor consolidation properties.
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, re-igniting 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.
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 Vikings.
Briquettes are virtually smokeless when burned in domestic fireplaces
and as such are widely used in Irish towns and cities where burning
non-smokeless coal is banned. Peat moss is a manufactured product for
use in garden cultivation.
