The Science of Bogs
A bog is a wet land, but this wetland is a very deceptive place. Although it can look (and sometimes feel) like land (perhaps with some small ponds or pools of water dotting the land, as well); in fact, it is more like a spongy "floating carpet" of land. Underneath the surface, the bog is full of water--about 90-95% water. Bogs are primarily composed of water and peat (which is decaying plants).
Bogs have different layers of peat. A cross section of a bog (above) shows that the peat layers change color. The lighter peat (weisstorf in German) is chunkier; the dead plants in it have decomposed less. This peat is called peat moss and is used primarily for gardening (though it has been used in animal pens since it's much more sanitary than straw). The darker peat (schwarztorf in German) is much denser and used for heat and fuel.
Bogs were considered strange and supernatural places by the early Europeans. They might talk to their gods and goddesses there...or even their dead relatives. They also knew bogs could be deadly and unforgiving. One misstep could cause a person to drown. For this reason, the early peoples of Europe built trackways through bogs so that they could travel safely. Many examples of trackways have survived; two are shown above.
Thousands of years ago, the early people of Europe thought that bogs were places where they could communicate with gods and goddesses as well as dead relatives. They made offerings in the bogs, to please the gods or perhaps to ask for something. Cauldrons, jewelry, and even wagons were deposited in the bogs to curry special favor.
Sometimes people were sacrificed in or near the bogs and buried there, as the ultimate offering. Because of the special chemical properties of a bog, bodies deposited there did not deteriorate. Even 2,000 years later, well-preserved bog bodies (with hair and skin and fingernails) have been discovered by peat cutters.
The people who placed the bodies there never suspected that they would be preserved in the bog water; they were not trying to make mummies.
Such preservation was an accident of nature; it happened because bogs provide an interesting burial environment. Although the bog mummies were buried below the surface, immersed in the bog water, their remains did not decay. Why? First, the bog-watery environment does not permit the growth of bacteria that will help decay flesh. Second, the bog water contains certain acids that act to tan the skin (much the same way as cowhide is tanned to produce leather). If the natural bacteria action is prevented and the skin is tanned, the conditions are right for producing a mummy.
However, much may also depend on the water table of the bog. Over thousands of years, it will raise and lower; the longer a bog mummy is above of the water table, the less well-preserved it may become over time. Many other factors may be involved, and scientists are still trying to understand the complete preservation process in a bog.
More information about the science behind the bog is explained in my book called Bodies from the Bog.