Ancient bones in disturbed peat bogs are rotting away, alarming archaeologists

Peat moss around a pool in Cairngorms National Park in the United Kingdom 

DUNCAN SHAW/SCIENCE SOURCE

The wrinkles on the face of “Tollund Man” are still visible, even though he died more than 2200 years ago. The mossy wetlands in Denmark that mummified his body are ideal for preserving organic matter, giving archaeologists an extraordinary window into our distant past. But a recent excavation at a similarly boggy site in Sweden shows these perfect conditions are fragile, and when they break down, so, too, do the bodies, bones, and other organic remains that have been preserved for centuries. The finding suggests a long-standing tenet of archaeology—avoiding excavation and leaving artifacts in the ground for long-term preservation—needs revisiting, at least for some wetland sites.

Anecdotal evidence has long suggested the condition of remains excavated from wetlands like peat bogs is declining, says Benjamin Gearey, a wetland archaeologist at University College Cork who was not involved with this study. For example, bone deterioration has been documented at Star Carr, an archaeological site in northern England. But it’s been hard to know how widespread the pattern is–and how fast the decay is occurring.

Ageröd, a peat bog in the south of Sweden that holds bones, antlers, and other artifacts from Mesolithic cultures that flourished more than 8000 years ago, is a good place to measure the pace of decay in a peat bog, says Adam Boethius, an archaeologist at Lund University. Boethius and his colleagues compared bones freshly excavated in 2019 with bones that had been exhumed from the bog in the 1940s and 1970s and stored in the Lund University Historical Museum. They rated the weathering of each bone, from well-preserved ones—those that were shiny and crack-free—to dull bones with worn outer surfaces.

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