Conservation conditions for organic material

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Girl from Egtved in a tree coffin in the National Museum of Denmark

Different conservation conditions are the trigger for the fact that no, few or many finds made of organic material can be recovered at archaeological sites with different soil conditions .

Conservation conditions

In the desert

In many deserts there is virtually no rain and no water. Organic materials are partially preserved very well due to the persistent drought. A particular stroke of luck is Egypt , where even papyrus, a pre-form of paper, has been preserved well over millennia, provided it was deposited in the desert, which often happens in the closed context of graves, but also in piles of rubbish that were created in the desert. Other deserts that are archaeologically rich in organic materials are the Syrian desert (see Dura Europos ), or the Taklamakan desert .

In the eternal ice

Under particularly favorable circumstances, organic materials end up in regions where temperatures are consistently below zero degrees Celsius; this is known as permafrost . Organic materials are frozen. The best-known example is Ötzi , a man from the Bronze Age who froze to death in the Alps and was only found in 1991. Another example are numerous tombs of the Scythian Pasyryk level , in which fabrics, wood and the well-preserved corpses of the grave owners were found.

In damp soil or in water

Due to the relatively low contact with oxygen under permanently moist conditions, the decomposition of organic material is slowed down so that even after a very long time large parts still appear in the diagnosis. Vegetable material in particular (wood, grass, linen and hemp) is retained. Depending on the alkalinity of the water, animal remains (bones, fur, wool) are only preserved to a very limited extent or not at all. Prominent examples are the lakeside settlements on Lake Constance and in Switzerland .

In the bog soil

The preservation of organic matter in peat bogs is mainly due to the high content of humic acids in the water. However, due to the strongly acidic environment, bones are usually not preserved. The rather calcareous moors are an exception. An example of this is the Danish bog sacrifice site Illerup Ådal in an alkaline bog (Muschelgytje with a pH value of 8.5), so that metal objects, wood, bones, antlers and vegetable fibers (cords) have been preserved while leather and wool have passed .

In oak coffins in burial mounds

The original assumption that the tannic acid contained in oak wood is responsible for the preservation of organic material can no longer be maintained today, since the amount of tannic acid contained in the coffin wood would be too low for a complete preservation of the coffin contents. The structure of the burial mound above and the chosen place for the burial often ensured permanent storage in the absence of air in a humid environment, so that almost the same conditions applied as for storage in the bog soil. This is particularly true of the Danish tree coffin burials of the Bronze Age , in which wool, leather, wood and plant material were preserved, but bones were not or only to a limited extent. Recent excavations indicate that such grave mounds with wet core were deliberately created by their builders.

In a very salty environment, in permafrost soil and with extremely low humidity

If textiles or other organic materials are stored under the specified conditions, the storage conditions prevent microbial contamination of the material and thus counteract decomposition by bacteria.

When in contact with metal corrosion products

If copper or ferrous metals and textiles come into contact, a relatively permanent combination of materials can result. In the corrosion of the metal under the action of moisture soluble metal salts penetrate the textile material. In addition, copper ions have a toxic effect that prevents the organic material from becoming infected with bacteria and thus can also contribute to preservation. In the course of storage in the ground, the materials combine chemically , and the textile components are broken down from the composite. As a result, the mechanical properties of the textile raw materials deteriorate, they are converted into browned and brittle fragments.

Bones in earth graves

The degree of preservation of bones depends on the surrounding material. Bone dissolution is caused by a chemical reaction in the surrounding earth that removes the lime from them. Once the bones are the only lime donor, they are quickly destabilized. However, if limestone or calcareous filler earth is also embedded, a degree of saturation will be reached before the bones are decalcified.

See also

Individual evidence

  1. ^ Mechtild Freudenberg: Grave mound and cult complex of the older Bronze Age by Hüsby, Schleswig-Flensburg district . In: Archaeological News . tape 14 , 2008, ISBN 978-3-529-01430-7 , pp. 30-32 .
  2. ↑ Ewald Schuldt : The Mecklenburg megalithic tombs. Investigations into their architecture and function (= contributions to the prehistory and early history of the districts of Rostock, Schwerin and Neubrandenburg. 6, ISSN  0138-4279 ). German Science Publishing House, Berlin 1972.

literature

  • Wijnand van der Sanden : Mummies from the moor. The prehistoric and protohistoric bog bodies from northwestern Europe. Batavian Lion International, Amsterdam 1996, ISBN 90-6707-416-0 (Original title: Vereeuwigd in het veen. De verhalen van de Noordwest-Europese veenlijken. De Bataasche Leeuw, Amsterdam 1996, ISBN 90-6707-405-5 (Dutch) ).
  • Karl Schlabow : Textile finds from the Iron Age in Northern Germany (= Göttingen writings on prehistory and early history. 15). Wachholtz, Neumünster 1976, ISBN 3-529-01515-6 .