Thursday, November 3, 2022

An experimental approach to lighting systems in Paleolithic caves

The first solid data about the presence of ancient humans in the inner parts of the caves (in places with total darkness, where artificial lighting is indispensable) was linked to Neanderthals, with evidence in Bruniquel Cave (France), where six anthropic circular structures formed by 400 fractured speleothems 336 meters from the entrance contained more than 18 traces of fire (probably burnt bones). A time of 176 ky BP has been proposed for this activity by uranium-series dating of calcite stalagmites, particularly the tops of stalagmites that are part of the structure (maximum ages) and of the bases of the stalagmite regrowth that seal the structures (minimum ages) [6]. There have been other proposals regarding human activity in the deep parts of caves, such as the deposit of human remains approximately 400 ky BP in Sima de Los Huesos in Atapuerca (Spain) [7], Dinaledi Chamber (South Africa) in 300–200 ky BP [8], Lamalunga Cave (Italy) in approximately 172–130 ky [9], or Vârtop Cave (Romania) in 60 ky [10]. Nevertheless, without considering the intentional origin of those remains, neither evidence of the use of fire, as in Bruniquel Cave, has been found at any Upper Paleolithic site, nor archaeological remains related to lighting proliferation has been found, especially remains associated with human uses in deep endokarst contexts linked to Paleolithic art. In those dark sites, combustion traces of three Paleolithic lighting systems have been recognized, particularly torches, fireplaces, and portable grease lamps [11, 12].

1.1.1. Torches.

Three peculiarities characterize the residues of torches: a) their dispersal location on the ground in caves, created by the intermittent fall of combustion residues (usually wood charcoals) along paths due to their use (such as the breadcrumbs in the story of Hansel and Gretel). b) Their location in the deep parts of the caves, where the artificial lighting is indispensable. We can be sure that the fire resources were used for artificial lighting in these places without discarding other additional activities (such as space markers, refueling sites, or with more cultural or symbolic meaning ones). c) The confirmation of its location in primary position (discarding those combustion remains coming from other contexts outside of the cave).

The residues of torches of Paleolithic age found in the caves’ inner parts are usually limited to scattered charcoals (Fig 1E) above different surfaces, and black marks on the walls and ceilings (Fig 1F).

Fig 1. Prehistoric lighting remains.

A. Fragments of semi-charred juniper branches covered by calcite in the cave of Aldène. Republished from ref. [16] under a CC BY license, with permission from Philippe Galant. B. Portion of pine wood in the Réseau Clastres Republished from ref. [14] under a CC BY license, with permission from Jean Clottes. C. Torch preserved in the mines at Hallstatt. Published under a CC BY license, with permission from Markus Roboch, CFO in Natural History Museum Vienna. D. Side view and illustration of the Star Carr torch Published under a CC BY license in ref. [17]. E. Scarred charcoal from Nerja Cave; F. Black marks from Nerja Cave; G. Fixed lamp from Nerja Cave. H. Fireplaces in a pit in Enlène Cave. Published under a CC BY license, with permission from Jean Clottes].

https://doi.org/10.1371/journal.pone.0250497.g001

Additionally, although they do not belong strictly to Pleistocene chronologies, there are some examples related to other hunter-gatherer societies that frequented the same caves as Paleolithic art.

For example, there is an outstanding vestige of a torch of Epipaleolithic age in the cave with Paleolithic art at Réseau Clastres (Ariège, France) that is linked with some kind of visits after Paleolithic graphic activity ([13, 14]: Fig 1B). This is an 11 cm long fragment, partially charred and covered with calcite, with a flattened cross-section. Furthermore, in this cave, there has been an enormous assemblage of scattered charcoals and black marks. The anthracological study of these charcoals determined the almost exclusive use of Pinus sylvestris (scots pine) for lighting in at least four different visits between 4.5–10.1 ky BP [13].

Other unusual vestiges of torches were found in the “Footprints Gallery” of the cave with Paleolithic art at Aldène (Hérault, France) [15, 16]. Again, there were dispersed pieces of charcoal and black marks on the walls also linked to the use of torches during the Epipaleolithic period (between 8.9–7.8 ky BP). Additionally, there are some small partially charred branches under a layer of calcite (Fig 1A). These remains are very useful for appreciating the thickness of the branches used for lighting. These vary between 1 and 2 cm wide and up to 27 cm long, although most of them measure between 10 and 20 cm in length.

Finally, other remains of torches found in other contexts but with prehistoric chronologies have helped conceive their potential morphology (for example, the outstanding example of Star Carr in the United Kingdom) (Fig 1D). Star Carr is an open-air Mesolithic site located in a peat bog on a riverbank. Over 200 rolls of semi-charred Betula sp. (birch) bark have been identified there, of which two were interpreted as torches. These two are of birch branch construction with the same species’ bark rolled around their distal end [17]. Moreover, numerous remains of torches used in salt mining have been preserved in Bronze and Iron Age mines at Hallstatt (Upper Austria, Austria). The wood generally came from fir in these locations and was cut into thin longitudinal sections up to 5 cm wide (Fig 1C) [18].

1.1.2. Fireplaces.

On the other hand, the remains of fireplaces related to lighting, like the remains of torches, are defined by their location in the deep and dark areas of caves, where their use for lighting is unquestionable (without discarding other additional possible functions such as space markers, refueling sites, or with more cultural or symbolic meaning ones). In these cases, the combustion residues are concentrated instead of scattered (as is the case for torches) and can include different types of remains: charcoal, burned bones, ashes, rubefaction, or soot. In Nerja Cave (Andalusia, Spain), for example, some residues of fire have been found in a natural concavity on a speleothem (Fig 1G). A multi-analytical methodology has characterized this fireplace and its remains of ashes, charcoals, and soot, dated by C14-AMS between 22,500–22,200 years cal BP, in the Solutrean period [19]. In Enlène Cave (Ariège, France), fireplaces inside clay hollows excavated in the floor in the cave’s deep parts have been found (Fig 1H). They have been attributed to the Magdalenian approximately 15,000 years cal BP [20], and they contain burnt bones and show the presence of rubefaction. Likewise, large fires have been documented in Chauvet Cave by a taphonomic study of heated walls [21, 22] and related through thermoluminescence analysis with the first phase of graphic decoration in the cave (37 to 33,500 years cal. BP) [23].

1.1.3. Portable grease lamps.

The use of portable stone lamps fueled with animal fat has been attested to by the location of hundreds of these pieces (or fragments of them) in contexts mainly attributed to the Magdalenian [11]. These lamps constitute a varied record and appear in different forms. Some of them were carefully prepared (a minority), others had only been altered slightly [24], and some flat or concave stones were used without any preparation [11, 25]. They functioned as open or closed circuits [11]. Most of the lamps employed a stone object (such as limestone, granite, or slate), but also shells were used [26], and it has been proposed that bone and vegetal objects were utilized [27]. Besides, other static lamps with higher volumes have been found (e.g., ref. [28]). In sum, numerous forms of Paleolithic lamps existed, but they all must fulfill the criteria to be defined as lamps: the scientific determination of remains or residues of combustion left by their use. This is the only proof that can differentiate lamps from other objects with a similar morphology (e.g., palettes to mix colorants) [11] or a simple natural formation (e.g., natural geodes). A suggestive appearance and shape, generally concave, suitable for use as a lamp, together with blackish or reddish marks on some part of them, were often sufficient for classification as a lamp in previous works. Indeed, numerous objects are described as lamps without any serious study to characterize them.

The combustion remains in Paleolithic lamps may take different forms: the carbonized remains of the wick; signs of smoke, soot, or rubefaction on parts of the lamp; or animal fat used as fuel preserved on it [29]. Until now, there have been very few examples of verification of combustion residues on Paleolithic lamps. The analysis of S.A. de Beaune is an exception in this issue [11]. Here, of the 302 objects examined might have been used as lamp, only 85 could definitely identified as such.



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