Blanket bogs began to form in Ireland about 4,000 years as the climate changed and early settlers cut down the forests to make agricultural land. This allowed minerals to wash out of the top soil and form a hard iron layer underground. Water could not drain freely causing the soil to become waterlogged and acidic. Dead plant material was preserved in the low oxygen, acidic environment and accumulates at an average rate of 1 MM per year. This overtime forms what is known as Peat (turf). Peat is still harvested as an important source of fuel. This harvesting seems to have started in the 17th century as the last of the native forests were cleared and an alternative form of fuel was needed. As a fuel turf has a higher carbon footprint (106 g CO2/ MJ) than coal (94.6 g CO2/MJ) or natural gas (94.6 g CO2/MJ). Peat bogs had considerable ritual significance during the Bronze Age and Iron ages and peat wetlands formerly had a degree of metallurgical importance as well. During the dark ages, peat bogs were the primary source of Bog Iron which is best known for its use in Viking arms and armour.
