In addition, peat bogs form in areas lacking drainage and hence are characterized by almost completely anaerobic conditions.This environment, highly acidic and devoid of oxygen, denies the prevalent subsurface aerobic organisms any opportunity to initiate decomposition.Such Iron Age bog bodies typically illustrate a number of similarities, such as violent deaths and a lack of clothing, leading archaeologists to believe that they were killed and deposited in the bogs as a part of a widespread cultural tradition of human sacrifice or the execution of criminals.
For these people, the bogs held some sort of liminal significance, and indeed, they placed into them votive offerings intended for the Other world, often of neck-rings, wristlets or ankle-rings made of bronze or more rarely gold. Many bog bodies show signs of being stabbed, bludgeoned, hanged or strangled, or a combination of these methods. In the case of the Osterby Man found at Kohlmoor, near Osterby, Germany in 1948, the head had been deposited in the bog without its body. Glob, "this probably indicates the wish to pin the dead man firmly into the bog." Some bodies show signs of torture, such as Old Croghan Man, who had deep cuts beneath his nipples.
In a number of cases, twigs, sticks or stones were placed on top of the body, sometimes in a cross formation, and at other times, forked sticks had been driven into the peat to hold the corpse down. Some bog bodies, such as Tollund Man from Denmark, have been found with the rope used to strangle them still around their necks.
Researchers discovered that conservation also required that they place the body in the bog during the winter or early spring when the water temperature is cold—i.e., less than 4 °C (40 °F).
The bog chemical environment involves a completely saturated acidic environment, where considerable concentrations of organic acids and aldehydes are present.
However, a CT scan of Grauballe Man by Danish scientists determined his skull was fractured due to pressure from the bog long after his death.
Amongst the most recent, the corpse of Meenybradden Woman found in Ireland dates to the 16th century and was found in unhallowed ground, with evidence indicating that she may have committed suicide and was therefore buried in the bog rather than in the churchyard because she had committed a Christian sin.
Strabo records that the Celts practiced auguries on the entrails of human victims: on some bog bodies, such as the Weerdinge Men found in the northern Netherlands, the entrails have been partly drawn out through incisions.
For example, the fractured skull of Grauballe Man was at one time thought to have been caused by a blow to the head.
The oldest known bog body is the skeleton of Koelbjerg Man from Denmark, who has been dated to 8000 BCE, during the Mesolithic period.
The overwhelming majority of bog bodies – including examples such as Tollund Man, Grauballe Man and Lindow Man – date to the Iron Age and have been found in northwest European lands, particularly Denmark, Germany, the Netherlands and the British Isles.
As new peat replaces the old peat, the older material underneath rots and releases humic acid, also known as bog acid.