Sciency Thoughts: Interpreting the life history of the Egtved Girl.

The ‘Egtved Girl’ was excavated near Egtved in Denmark in 1921, one of a series of Bronze Age burials in Oak coffins placed within barrows (raised burial mounds) in the area dated to between 1000 and 1500 BC. Egtved Girl was between 16 and 18 years old at the time of her death, and buried in an Oak coffin dated dedrochronologically (i.e. using tree rings) to 3400 years ago. The interior of the coffin was flooded with slightly acidified water, which had led to good preservation of the sort tissues, but dissolution of the skeleton with only dental enamel remaining. She was dressed in well-made woollen clothing including a short corded skirt and a short blouse, interpreted as a sign of a high social status (as are Oak coffins and burial mounds), with a leather belt with a large disk-shaped bronze ornament, which has been suggested may indicate she was a priestess of a Nordic Sun-worshiping cult, and a variety of other grave goods. A small container was placed by her head, containing the cremated remains of a child thought to have been aged 5-6.

In a paper published in the journal Scientific Reports on 21 May 2015, a group of scientists led by Karin Margarita Frei of the National Museum of Denmark and the Danish National Research Foundation’s Centre for Textile Research at the University of Copenhagen describe the results of a multi-disciplinary investigation into the Egtved Girl remains, intended to elucidate her movements during her lifetime.

A photo of the remains of a Bronze Age high status female found inside an oak-coffin in a monumental burial barrow at Egtved, Denmark. The Egtved Girl’s garments are extremely well preserved and her exceptional wool costume consists of several wool textile pieces as well as a disc-shaped bronze belt plate, symbolizing the sun. Roberto Fortuna/National Museum of Denmark. Frei et al. (2015).

Attempts to extract DNA from the hair of Egtved Girl failed, probably due to the acidic conditions inside the coffin, which is not a good environment for DNA preservation. However isotopic ratio analysis proved to be much more applicable and was applied to a number of tissues and fibres from the burial. Strontium has two stable isotopes, strontium-86 (⁸⁶Sr) and strontium-87 (⁸⁷Sr), and the ratio of these in tissues is derived from that in groundwater where a person or animal lives, which in turn is determined by the local geology.

The first strontium isotope ratio test was carried out on the enamel of the first lower left molar. This is laid down between birth and 3-4 years of age, and its isotopic ratio is subsequently fixed for life. The enamel yielded an ⁸⁶Sr/⁸⁷Sr ratio of 0.71187; this is very high compared to the value obtained from soil in the Egtved area, which yielded results ranging from 0.70852 to 0.70874, indicating that the girl had not spent her childhood in the area. Such high values are not found anywhere in Denmark with the exception of the (remote) island of Bornholm, but are found in other areas of Europe, such as southern Scandinavia, southern Germany, France and much of the UK.

Next an isotope ratio from a fragment of occipital bone from the cremated child. Bone, unlike tooth enamel, is constantly replaced throughout life, albeit at a slow rate, so isotopic information obtained from it is typically an average of the ingested ratio over the last few years of life. In this instance the bone fragment yielded an ⁸⁶Sr/⁸⁷Sr ratio of 0.71190, comparable to that obtained from the tooth but incompatible with local soil values, indicating that the child too had come from outside the area.

Frei et al. then took a hair from the scalp of Egtved Girl from analysis. Hair is constantly produced by the body, and the isotope ratio within a piece of hair remains fixed at the point when it grew. This means that a long hair can contain a record of the isotopic composition of ingested strontium for months or even years. A 23 cm length of hair was obtained from the girl, and divided into four lengths of about 6 cm each. The hair segment closest to the scalp, thought to have been produced in the last 4-6 months of life, yielded an ⁸⁶Sr/⁸⁷Sr ratio of 0.71229, again not close to anything found in the Egtved area, suggesting that she had spent this part of her life away from the area, but the middle two segments, thought to represent a period of at least nine months, produced ratios of 0.71028 and 0.71086 slightly high for the Egtved area, but certainly compatible with her having lived in Denmark for this period and possibly having had spent some of her time close to the burial site. The final fragment, thought to have been produced at least 13 to 23 months prior to death, yielded an ⁸⁶Sr/⁸⁷Sr ratio of 0.71255, again incompatible with her having lived in Denmark for this part of her life. Taken together these results suggest a fair amount of mobility on the part of Egtved Girl during the last two years of her life.

An additional study of the microstructure of Egtved Girl’s hair suggested that she had gone through several periods of sharply reduced protein intake during the period when it was growing, but an attempt to obtain DNA for analysis from the hair failed (which is unsurprising given the acid environment inside the girl’s coffin).

Next Frei et al. took a series of samples from one of Egtved Girl’s fingernails for analysis. Isotopic levels in nails are laid down in a similar way to those in hairs, though nails are rather slower growing, giving a more detailed glimpse into the last moths of life. The nail samples are thought to represent a period covering the last 4-6 months of life (similar to the first 6 cm of hair), and yielded ⁸⁶Sr/⁸⁷Sr ratios of 0.71235 to 0.71240, similar to that obtained from the youngest hair, and again incompatible with the period having been spent in Denmark.

Drawing depicting the sampling strategy to reconstruct a high-resolution life-mobility-timeline of the Egtved Girl. Tooth enamel was sampled to reconstruct the first years of her life, segments of scalp hair to reconstruct, at least, the 23 final months of her life as well as segments of one of her fingernails to reconstruct the final approximately 6 month of her life. Marie Louise Andersson/National Museum of Denmark in Frei et al. (2015).

The clothing of Egtved Girl was made of high quality woollen material. Fibres from this were also analysed, yielding ⁸⁶Sr/⁸⁷Sr ratios ranging from 0.71168 to 0.71551, indicating that the material had also originated from outside Denmark. However fibres from a woollen cord from the container with the cremated remains of the child yielded results ranging from 0.70982 to 0.71044, consistent with local manufacture.

The majority of ⁸⁶Sr/⁸⁷Sr ratios recovered from Egtved Girl and associated remains exceed 0.711, to high for anywhere within Denmark, or within several hundred kilometres of its border, but consistent with a wide range of areas within Europe. The grave goods found with the body are archaeologically consistent with a culture found in the period from southern Germany to southern Scandinavia, in which alliances between chieftainships are believed to have been cemented by marriages to high-ranking women, leading to a high level of mobility among women of noble status. Egtved Girl appears to have moved long distances several times within the last two years of her life, and had travelled from an area outside of Denmark shortly prior to her death. Based upon the strontium isotope ratios in her tissues and the nature of her grave goods, Frei et al. suggest that it is most likely that she originated from the Black Forest region of southwestern Germany.

Map showing the location of the Egtved burial site (red dot). Borders of the nearest areas with bioavailable ⁸⁷Sr/⁸⁶Sr values that potentially fit the tooth enamel, the child’s bone, wool garments and oxhide belonging to the Egtved find are marked with green lines and arrows. Of these regions the Black Forest area (red ellipse) appears to be the most plausible place of origin as constrained by the multiple strontium isotope codes contained in materials from the Egtved find combined with the archaeological artefact record patterns. Marie Louise Andersson/National Museum of Denmark in Frei et al. (2015).

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Friday, 19 June 2015

Interpreting the life history of the Egtved Girl.