Peat forms when plant material is unable to decay completely. This usually occurs in wet areas that do not provide the correct acidic and anaerobic conditions for full decay.
Decomposed plant mixtures, or humus, accumulate in a watery environment without oxygen and become peat. Atmospheric temperatures must be warm enough for plant growth but also low enough that microbial activity is disrupted so that plant matter does not break down completely.
Peat is made up of primarily wetland vegetation. This includes bog plants such as mosses, shrubs and sedges. Most of the peat bogs that exist today formed since the retreat of the glaciers after the last ice age around 12,000 years ago. Scientists believe that the peat in these peatlands has been forming for 360 million years.
Peatlands are wetlands that are characterized by semidecayed organic matter that is produced at a rate greater than its decomposition. Peat forms and holds water, which creates wetter conditions in an area and can cause the wetland it inhabits to expand. Peatlands can include raised bogs, ponds and ridges. Over 90 percent of all peatlands are located in the temperate and cold belt of the Northern Hemisphere. The rest is found in tropical and subtropical areas.
Dried peat can be used as fuel. Countries such as Ireland and Scotland have peat harvesting industries. Traditionally, peat replaced wood as fuel for cooking and heating in these countries because trees were not always readily available.