Peat Bogs Are Freakishly Good at Preserving Human Remains

body bog — The Tollund Man was discovered in a Denmark bog in 1950 with skin so well-preserved, the wrinkles on his face are still clearly visible. Flickr/CC BY-SA 2.0

Bogs are monuments to death; they're created by generations of dead, buried plants. They're also havens for mummies. Artifacts buried beneath bogs — including human bodies — may be kept in astonishingly good condition for thousands and thousands of years. They've all got stories to tell, and today we'll look at the weird science that makes their preservation possible.

Common in cool, wet parts of the world, bogs are waterlogged grounds that form when decaying plant matter — known as peat — accumulates in a low-lying areas. Bogs are usually found in cool climates and often in lake basins created by ice age glaciers that no longer get a steady flow of river or stream water. Over time, mosses cover the heap like a blanket, and in most cases, this mossy layer is primarily made of sphagnum.

Sphagnum moss has the power to transform an entire landscape. Water or dirt caught beneath sheets of it will stop getting a normal supply of oxygen from the atmosphere. Also, sphagnum soaks up calcium and magnesium, which makes the underlying soil and water mildly acidic.

Since bacteria and fungi find those conditions inhospitable, the dead vegetation decomposes at a phenomenally slow rate. Instead of breaking down right away, it lingers. Piling up over time, masses of the botanical waste gradually turn into peat, a soggy, mud-colored substance.

Peat can be used as animal bedding and as a fossil fuel, which makes it an important commodity in places like the Irish midlands. But to archaeologists, peat is a lot less valuable than the Homo sapiens corpses that sometimes come with it.

Iron Age CSI

Bogs have long fascinated humans not just for their fossil fuels. The spongy soil, which often burns, has intrigued people as far back as the Bronze Age. Many people died in these bogs or were placed there after their deaths. And these bog bodies, as they're known, have been found all over the world.

The wetlands of northwestern Europe, for instance, is a bog body hub. Hundreds of these corpses have turned up in Germany, England, the Netherlands and neighboring countries. In 2011, peat harvesters working in Ireland's Cúl na Móna Bog accidentally ran over a Bronze Age corpse with a milling machine.

Dubbed the "Cashel Man," the harvester found all that was left of an adult male who'd probably died in his 20s. His body was riddled with injuries, including a broken arm and a nasty cut across the backside. Some of these may have been caused by the compressing weight of the bog moss above him — or the blades of that milling device. Nevertheless, archaeologists have reason to suspect that the Cashel Man was a ritualized sacrifice victim.

(Stab wounds, slit throats and evidence of torture have been observed on other European bog bodies. Historians think the local wetlands were once a hotbed for religious sacrifices.)

Carbon dating tells us the Cashel Man perished about 4,000 years ago, seven centuries before King Tut was born. To date, he's the oldest European bog body on record with intact skin. That's right: The corpse of somebody who's been dead for four millennia still has its skin attached.

And this isn't a fluke. Lots of bog bodies retain some or all of their original skin. The Tollund Man, a 2,300-year-old corpse recovered from a Denmark peat bog in 1950, has skeletonized hands, but elsewhere his skin is so well-preserved that little details like the wrinkles on his forehead are still visible.

Skin Care Secrets

Although the Tollund Man's skin didn't rot away, the mummification process did change its appearance and texture. Like the Cashel Man, the Haraldskjaer Woman and lots of other bog bodies, he's got quite a tan going on.

Bog mummies often sport leathery, dark brown skin. (Some of them also have preserved hair that was dyed red after death.) This is most likely caused by sphagnan, a recently discovered polymer that seeps out of dead sphagnum moss. Leather is made through a process that strengthens the bonds between some of the natural fibers in animal hides. As a tanning agent, sphagnan has the same effect on human skin, rendering it tough and tea-colored.

Sphagnan also binds with nitrogen, which bacteria need to survive. So by removing nitrogen from the environment, sphagnan helps prevent the spread of microorganisms that would normally be breaking down human and animal remains. And furthermore, sphagnan — along with the acid that it turns into — pulls calcium right out of dead bodies.

Bones get weakened in the process. Although sphagnan does a fine job of preserving skin, its calcium-thievery isn't great for skeletons. Mummies have been found in certain bogs with soft, extra-flimsy bones that are about as sturdy as cardboard and that have been distorted by heavy peat.

But that's assuming the decalcification process doesn't altogether eliminate them. Lots of bog bodies have been found missing bones, and some of the mummies are totally boneless. The latter are basically human-shaped bags of leathery skin wrapped around some pickled organs.

Boning Up

Not all bogs are so hostile to bones, though. The water's acidity level varies from bog to bog, and this impacts corpse preservation. Archaeologists have discovered that in really acidic peat bogs, the resident mummies have lots of skin and soft tissue, but weak or nonexistent bones.

But there are some boggy places with relatively alkaline — or "basic" — water. Here, the environment pretty much has the opposite effect on corpses. Look at the Windover Archaeological Site, a peat-bottomed pond in Florida that became the final resting place for dozens of Native Americans between 6,990 and 8,120 years ago.

Skeletal remains from 168 people have turned up in the peat. A large deposit of crushed-up snail shells lying under the pond supplies the water with magnesium and calcium carbonates. That makes the water more alkaline, neutralizing the sphagnan to an extent. Instead of mummified skin bags, the bog is rife with naked bones and skeletons. Bare as they are on the outside, the ancient bones had a big surprise in store for scientists: Brain tissue was found in more than 90 of the Windover pond skulls.

Originally Published: Jan 23, 2019