Archaeology Magazine Archive

A publication of the Archaeological Institute of America

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(Robert Clark)

Bogs are rich sites for the imagination. Not quite land, not quite water, they are both seductive and treacherous. Perhaps most baffling is their uncanny ability to preserve organic material. It's counterintuitive. Why should a place so damp and fetid—nearly a swamp—preserve anything? It has to do with how inhospitable the conditions in a bog are for the bacteria that usually do the business of decomposition.

Bogs form when moss accumulates in low-lying patches of land. The moss saturates the soil with water and prevents oxygen and nutrients from circulating in. The bacteria normally responsible for the breakdown of organic material cannot function without oxygen, leaving behind a wet, mostly undecomposed mash. The growth of more moss on top continues the cycle, covering old peat with new. This buried organic material breaks down a little and releases a complex and poorly understood cocktail of chemicals, some of which have preservative properties. Conditions in some bogs can be as acidic as vinegar, which can have effects similar to the process of tanning, further preserving organic material, though different tissues react differently to the conditions. The acid in some bogs, for example, dissolves the calcium phosphate in bone.

However, bog ecosystems are complex, and there can be many variations in chemistry, water levels, and even temperature across relatively small areas. The differences between these microenvironments often determine what a bog preserves and what it leaves to rot. A body might cross several microenvironments, preserving certain parts of a body and leaving others to decay. Tollund Man, for example, has immaculately preserved feet, while his hands have been skeletonized.

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