Chewing Tar in the Early Holocene: An Archaeological and Ethnographic Evaluation

Article excerpt

Introduction

Amorphous lumps of putative tar with human tooth impressions have been recovered from several prehistoric sites in Scandinavia (e.g. Bang-Andersen 1976; Larsson 1982; Johansson 1990; Regnell et al. 1995; Hernek & Nordqvist 1995), southern Germany (Rottlander 1981, Schlichtherle and Wahlster 1986, Alexandersen 1989) and Switzerland (Schoch 1995). The term 'tar' is used here to refer to a product of the destructive heating of wood, bark or resin. Although small in number, these finds date to the Mesolithic and Neolithic periods and can be described as hardened lumps or shapeless masses, brown to black in colour, with distinctive tooth impressions. Similar, although apparently unchewed lumps of tar have also been recovered (e.g. Clark 1954: 167; Larsson 1983: 75; Binder et al. 1980; Cattani 1993). Although mentioned briefly in site reports, the scarcity of such finds combined with the difficulty in identifying amorphous samples of organic matter has limited evaluation of their origin and use. More recently, efforts to characterize organic resinous substances, considered to have been used to fulfil a wide range of non-dietary functions, including use as adhesives and sealants in prehistoric Europe, has stimulated greater interest in these finds and this note addresses some of the Scandinavian examples (see also Aveling 1997). This work forms part of a larger project into the use of molecular marker compounds to identify organic natural products from Mesolithic sites in northern Europe (e.g. Aveling & Heron 1998).

Background

Recent chemical investigations of adhesives, sealants, waterproofing agents and other amorphous organic substances from prehistoric contexts in Europe has confirmed the widespread use of birch (Betula) bark tar (Pollard & Heron 1996). Birch-bark tar is a black-brown product obtained by the destructive heating of birch bark in a vessel or oven with a limited supply of air. Molecular information, obtained principally by gas chromatography/mass spectrometry, has been highly successful in identifying a number of archaeological samples from the Neolithic onwards (e.g. Sandermann 1965; Hayek et al. 1990; 1991; Reunanen et al. 1993; Heron et al. 1991; Binder et al. 1990; Charters et al. 1993; Regert 1996; Regert et al. 1998). Identification is based on the recognition of a suite of triterpenoid molecules mostly based on the lupane carbon skeleton, including betulin, lupeol and lupenone. These molecules are consistent with those present in authentic fresh birch bark, taking into consideration modifications to the carbon skeleton due to thermal effects as the bark is heated and alteration during long-term burial. As the references above testify, the recognition of birch-bark tar in the toolkit of Neolithic Europe is becoming a common occurrence. For example, it features among the frozen remains of the Neolithic body recovered from a glacier in the Otztal Alps on the Austrian-Italian border. The copper axe, arrowheads and arrow flights were hailed using birch-bark tar as the adhesive medium (Sauter et al. 1992; Spindler [TABULAR DATA FOR TABLE 1 OMITTED] 1994: 89,124-5). Regert (1996) has conducted a systematic study of tar samples from two Neolithic sites (Chalain, Jura and Giribaldi, Nice) in France. Birch-bark tar was characterized in nearly all cases, although mixtures of birch tar with other plant products were also identified. One of the samples from Chalain was not consistent with a birch origin and is considered to represent the exploitation of non-local fossil bitumen seepages (Regert et al. 1998). Other alternatives to the use of birch-bark tar in Neolithic and later contexts in northern Europe include a bituminous substance on an Early Bronze Age knife from Xanten-Wardt, Germany (Koller & Baumer 1993), a Pinaceae tar, possibly from Pinus spp. (Heron et al. 1991), and beeswax (Heron et al. 1994) on Neolithic pottery fragments from Ergolding Fischergasse, Germany. …