Where they were found
Bog mummies have been found in the cold, watery peat bogs of Ireland, Scotland, England, the Netherlands, Germany, Denmark, and Sweden.
The only other place (besides northern Europe) to produce bog mummies is Florida (Windover Pond, though the preserved remains there were not entire "bog bodies" but "bog brains:" early native Americans used the pond as a burial site from which scientists recovered some skeletal remains in the mid-1980s; the preserved brain matter inside some skulls was able to provide DNA samples.
Topic to research: Why are bog bodies primarily found in northern Europe?
When they were found
Bog mummies are accidental mummies, made only by nature. In northern Europe, the people who became bog mummies usually died from 2000-2500 years ago, though some are even older and others much more recent. The preserved brain matter from Florida dates to 7000-8000 years ago.
Topics to research: How do scientists determine the time of year when a bog mummy died and how long the person has been dead?
How they were made
Bogs provide an interesting burial environment. At first glance, a bog may look like solid ground, but it isn't; it's quite spongy and may feel as if it's going to give way. That's because, under the surface, a bog is made up of about 90 percent water. The water is filled with peat (decaying plant matter).
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.
One final note: even a bog skeleton is considered a bog mummy by scientists studying these mummies. A skeleton is often produced in a fen, while a non-decayed bog mummy will only come from a bog.
Topics to research: Explain exactly how a bog preserves a human body and keeps it from deteriorating. What materials and chemical processes are involved?
How many were made
No one knows how many people were buried in bogs, but the number does not seem to be high based on the few bodies recovered.
It has also been difficult for scientists to determine how many bog mummies have been found in bogs, even though quite a few people have tried to count them. The problem is that accurate records were not kept until perhaps the middle of the 20th century. Early accounts from the 1600s even to fairly recent times are often too dramatic to be believable--and (if the body was not saved--most weren't) completely impossible to validate.
Topic to research: Read some early accounts of bog body discoveries and question their validity with your own analysis.
What's special about them
1. Bog mummies are often quite well preserved, arguably even better preserved than almost all Egyptian mummies. But the issue that seems to attract most attention to these mummies is the nature of their death and burial: were they human sacrifices or are there other explanations to account for their deaths.
For example, Borremose Woman (right) appears to be a sacrifice to many scientists, but at least one believes that she may have become trapped in the bog and (as she was drowning) was attacked by predators. The truth is that no one will ever know what really happened to her or most of the other bog mummies that have been discovered.
2. Interesting objects have also been discovered in bogs, including the Gundestrup cauldron.
Topics to research: Read the stories about the bog mummies posted on this site and categorize them by their suspected manner of death.