How do bogs keep things fresh?

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July 28 2006 6:50 PM

Bless This Boggy Book

How do bogs keep things fresh?

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A construction worker discovered an ancient book of psalms while excavating an Irish bog last Thursday. Ireland's National Museum has called it "a miracle find" and labeled the 1,200-year-old tome the "Irish equivalent to the Dead Sea Scrolls." How could the book have survived for so many years in a bog?

European peat bogs happen to be excellent at preserving organic matter. Bits of animal skin—like the vellum pages upon which the ancient psalter was written—can last for hundreds or thousands of years when they get trapped under the surface of peat at the top of a bog. That's because they're exposed to an acidic environment with lots of sphagnum moss and very little oxygen. These factors make life very hard for the microbes that would otherwise cause rotting and decomposition.

Daniel Engber Daniel Engber

Daniel Engber (@danengber) is a columnist for Slate. Send him an email at danengber@yahoo.com.

The sphagnum moss produces an antibiotic substance called sphagnan that staves off rot in several ways. First, it binds with proteins on the surface of microorganisms in a way that immobilizes them and removes them from the water. Second, its highly reactive carbonyl groups can alter the chemicals and nutrients that would be necessary for the decomposition of a piece of organic matter. Third, the sphagnum moss causes the organic matter to undergo certain chemical changes that make it more impervious to rot—in much the same way that animal skins can be preserved as leather.

The peculiar properties of these bogs have made them invaluable archaeological repositories. More than 1,000 specimens of well-preserved human remains have been found under beds of peat moss. These "bog bodies" can retain their key features for thousands of years. In many cases the chemicals in the bog break down the skeleton and leave only the soft tissue. The tanning reactions from the sphagnum moss give the skin on these remains their characteristic dark-brown color.

Among the bog bodies, the most famous is the Tollund Man of Denmark. * He died in about 350 B.C., but you can still see the stubble on his chin, and the rope that killed him remains tied around his neck. The Lindow Man, who was found in England in 1984, still has a beard and a mustache. Researchers say his killers struck him on the head, cut his throat, and strangled him before tossing him into the bog.

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* Correction, July 31, 2006: This piece mistakenly identified Tollund Man as being from Norway. The body was found in Denmark. (Return  to the corrected sentence.)