Neandertal Fire Technology

Neanderthal Fire Technology Project – Final Report Carolina Mallol, Cristo Hernández, Dan Cabanes, Ainara Sistiaga Jorge Machado, Leopoldo Pérez, and Ágata Rodríguez November 15, 2014 2

Introduction Our ongoing research on Neandertal fire technology is part of a multidisciplinary project ongoing since 2010 with full support of the Leakey Foundation. The ultimate goal of our project is to generate a corpus of experimental and ethnoarchaeological data on different behavioral variables related to combustion activities that can be used as analytical tools for the study and interpretation of the Middle Palaeolithic record. As of today, we have obtained significant results, which have been presented in international conferences and published in widely read international peer-reviewed journals.

Our starting goals for the current grant were the following: To investigate taphonomic aspects of some of the experimental 2010 fires left in situ.

To investigate relighting, an aspect of combustion whose identification is problematic (according to the results of our 2010 experiments).

To investigate different aspects of combustion on stony substrates.

To carry out an archaeological excavation season at Abric del Pastor, a Middle Palaeolithic site with evidence of anthropogenic fire on stony substrates, dating to more than 75,000 years ago.

To carry out lipid analysis of sediment from a selection of our 2010 experimental fires.

We approached these goals with an interdisciplinary method previously applied in our first project (NFT-2010). The method is based on integration of macro and micro-scale analyses of the sedimentary context of experimental and archaeological combustion structures, as well of any material remains (lithics, bones and charcoal) associated with them. For the experimental fires, we also analyzed the temperature record. The microstratigraphic techniques implemented for the analysis of sediments included: 1) Micromorphology using transmitted light microscopy, 2) Mineralogy using Fourier Transform Infrared Spectroscopy (FTIR), 3) Phytolith analysis and 4) Lipid analysis using Gas Chromatography-Mass Spectrometry.

Integration of these techniques allowed us to describe anthropogenic combustion contexts in great detail and understand the interaction between different variables that play a role in the formation of the archaeological combustion features.

Below, we outline the main outcomes of our 2013-2014 investigations.

Results 1. Taphonomic aspects Ten experimental combustion structures from our 2010 experiments were left in situ for taphonomic study. These have been described yearly since then. Four hearths left in the open air have been completely invaded by vegetation and mesofauna are barely visible (Figure 1, Area A). One hearth left in the open air but sheltered by its position at the foot of a tall travertine wall appears intact (Figure 1, Area C). One hearth left at a cave entrance appears intact except for slight superficial 3

reworking of the ashes and deposition of excrements, both caused by a small carnivore (Figure 1, Area D).

Two of these experimental combustion structures, NFT-10-1, an open-air fire and NFT-10-21 at a cave entrance were sampled in 2013 and analyzed microstratigraphically (Figure 1). The unsampled halves of these combustion structures were left in situ for future investigations. In addition, we made a new fire adjacent to NFT-10-21 to begin comparative taphonomic monitoring. Overall, we noted that the preservation of the ash after three years is excellent. However, we noticed an increase of phytolith weathering in this structure, probably produced by the alkaline sedimentary environment derived from the excellent ash preservation.

Figure 1. Sampling of experimental open-air fire NFT-10-1 (after three years). Note the fresh appearance of the ash.

2. Relighting A new fire was made on top of NFT-10-20, one of the 2010 experimental cave entrance fires that had been left in situ (Figure 2). No visible stratigraphic contact was observed in the resulting combustion structure. The structure was left in situ for future relighting and microstratigraphic sampling.

Figure 2. Relighting of experimental cave-entrance fire NFT-10-20 (after three years).

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3. Combustion on stony substrates For this goal, we studied combustion structure H6 from Abric del Pastor Middle Palaeolithic site (Alicante, Spain). This structure, excavated in 2009, was found on a cobble-rich layer of the site and appeared as a circular area in which three overlapping beds of cobbles had a “burnt� appearance, with red or black zones on their surfaces (Figure 3). Thus, a question was raised about the temperature or kind of combustion needed to reach such heat penetration depths.

Figure 3. Archaeological combustion structure H6 from Abric del Pastor (Middle Palaeolithic) consisting of a circle of cobbles with red and black zones on their surfaces. GIS vertical plot of the cobbles and associated archaeological material.

To investigate this issue, we carried out a series of experiments to replicate this archaeological context. We made five experimental open-air fires on stony substrates, stacking up to three layers of cobbles collected at Abric del Pastor (Figure 4). Some of the cobbles had thermocouples attached to them. Two of these, NFT-13-28 and -30 were excavated after four months. Ash and soot were sampled for geochemical analysis.

Figure 4. Experimental fires on stony substrates. Note the presence of ashy patches after a rainy winter.

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During the experiments, we noted calcination of the upper row of cobbles and random reddening and blackening of the rest. Most of the ash percolated through the cobbles and accumulated at the base. After a rainy winter left in the open air (4 months) there was further ash percolation and interestingly, formation of a thin crust in some of the ashy patches. To our surprise, much of the ash was still in place (Figure 4).

The cobbles attached to thermocouples were sectioned and described and the same was done for a selection of archaeological cobbles from H6 for comparison. The main outcomes of this analysis are: 1) Thermal alteration on the cobbles is only visible when heating exceeds 200째C and 2) Thermal alteration shows different macroscopic features depending on the relationship between heat diffusion and calorific energy. This observation has significant implications towards our understanding of the preservation potential of archaeological combustion features and opens up a new research line to explore the relationship between fire intensity and fuel supply.

In addition, the experimental cobbles were thin sectioned and observed for crystallographic changes and their mineralogy was analyzed using FTIR. Overall, although the temperature reached up to 800째C no crystallographic or mineralogical change was identified. However, FTIR analysis of ash samples from fire NFT-13-30 shows formation of plaster. The ash from this hearth was produced at high temperatures (>750째C) and the calcitic ash was decomposed into lime. The lime then reacted with ambient humidity overnight, transforming back into calcite but in a molecular structure similar to what we know as construction plaster.

4. Abric del Pastor Excavation We carried out a month long excavation season at Abric del Pastor in July 2014. Large surface excavation (approx. 40 m2) enabled us to unearth a complete sedimentary unit (Unit IV-d), which yielded four combustion structures: H8, H9, H10 and H11 (Figure 5). These were sampled and excavated, and later investigated using microstratigraphic techniques. We also sampled three additional combustion features: One from a small unexcavated bench preserving an overlying unit (H7 in Unit II) and two stacked features from Unit VI in the deep sounding (H12 and H13, Figure 6).

Excavation of the deep sounding yielded burned flint artifacts, and these were collected for TL dating.

Unfortunately, as noted in our six-months report, TL dating results were negative.

The data point to the existence of two in situ reworked combustion structures, H8 and H9, representing fires made on unvegetated substrates. GIS plots of the associated archaeological remains suggest the presence of a hearth-related assemblage with a concentration of material around the structure and none within. Combustion feature H10 shows scattered charcoal and no strong evidence of in situ combustion. Micro-combustion residues in this sample are well rounded, indicating secondary positions. Furthermore, no FTIR ash signature was identified in the H10 samples and the spatial distribution of the lithic and faunal remains as plotted in a GIS are not suggestive of a hearthrelated assemblage. Control sediment samples collected outside the combustion features do not show significant presence of combustion residues.

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H9

H10 9

H11 H8

Figure 5. Archaeological combustion features H8, H9, H10 and H11 found at Abric del Pastor Unit IV-d.

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b

Figure 6. Archaeological combustion features found at Abric del Pastor Unit II (a) and Unit VI (b).

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The sedimentary structure of Unit IV-d is very open and loose and composed almost entirely of limestone gravel, sand and calcitic dust. Thus, individual small-sized particles on this type of substrate can be easily reworked by trampling. Indeed, in H8 and H9, the presence of granular microstructures, rounded bundles of sediment containing highly fragmented, silt-sized charcoal and ash, and a mix of burnt and unburnt microscopic bone fragments indicate trampling of the original combustion features (water could also lead to rounding but no other micromorphological features indicative of water flow was identified). This is in agreement with FTIR and phytolith analyses data showing random presence of ash among samples and severely altered phytolith assemblages.

Finally, H12 and H13 from the deep sounding show in situ combustion residues and a considerable amount of ash.

5. Lipid analysis of NFT-2010 combustion structures As an extension of our 2010 results on the nature of black layers of archaeological hearths as representing burnt soils on which fires were made, we incorporated two specific actions geared to strengthen our previous study. First, sediment samples from experimental fire NFT-10-15 and archaeological hearth H33 from El Salt Unit X were analyzed to test for the presence of lipid molecules using Gas Chromatography- Mass Spectrometry (GC-MS). Preliminary data from NFT15 and H33 shows a n-alkane fraction coherent with heat propagation in the soil substrate: 1) An ash layer exhibiting stronger alteration from heat (more evident in H33 than in NFT-10-15); 2) A black layer showing slight alteration by heat as observed in smoothing of the peaks and a decrease of the odd/even predominance; 3) A reddened basal layer and unaltered underlying soil – as observed in the clear odd over even carbon predominance and absence of smoothing.

In sum, our results support the black layer hypothesis. We initially planned to carry out a larger number of samples, but the analysis had to be postponed due to the impossibility to gain access to a GC/MS at University of La Laguna. Nevertheless, all the saples have been prepared and are ready to be analyzed in a GC/MS. We will analyse the remaining samples at the Geobiology Lab in MIT in the spring of 2015.

6. A new fire on a bed of dead leaves A new small fire was made on a substrate of dead leaves to investigate the composition of the resulting black layer in comparison to a sparsely vegetated or bare substrate (previously documented in our 2010 experiments). We used Celtis leaves, which have been identified extensively in the sedimentary record of El Salt Middle Palaeolithic site (studied in the 2010-2011 project).

Micromorphological analysis of a sample from this hearth shows that the charred leaves resulting from this experiment clearly underlie the ash layer and do not mix with it (Figure 7). These results support our previous black layer hypothesis (Mallol et. al., 2012).

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Figure 7. Experimental fire made on a bed of dry Celtis leaves and photomicrograph showing how these do not mix with the overlying ash.

Conclusions The results of our 2013 Neanderthal Fire Technology Project investigations have provided new sources of information that can be used to approach Middle Palaeolithic combustion features. In our 2010 investigations, we focused on sandy-clayey substrates and observed that black layers of simple hearths may represent burnt organic-rich occupation floors. In the 2013 research we obtained further supporting data from burning on a leaf litter substrate and complemented our previous results with preliminary molecular data on lipids trapped in the sediment of combustion structures, highlighting the importance of lipid analysis in the study of archaeological fire. In addition, we studied ten experimental fires left in situ since 2010 and observed their excellent states of preservation.

Besides, we focused on stony substrates and showed that low temperature burning (<200째C) is difficult to detect both visually and geochemically. Nevertheless, our experiments show that simple fires made with pine wood on stony substrates composed of several layers of cobbles may reach high temperatures (>700째C) and encompass significant heat penetration, as observed in the color change and temperature record of cobbles. With this experimental data at hand, we carried out archaeological excavations at Abric del Pastor, a Middle Palaeolithic site older than 75,000 years, unearthed several combustion features and undertook their study. The study incorporated macro and micro-scale analyses and yielded important information towards interpretation of Neanderthal combustion features. First, we corroborated the primary nature of two of the features (H8 and H9) and determined that they were trampled. In addition, our experimental data on stony substrate fires suggest that H6 possibly reached very high temperatures. Finally, the presence of very well preserved in situ combustion features in the deep sounding (Unit VI) motivates further excavations at the site.

The results of this project have been presented in the UISPP Conference (Burgos, 1-7 September) and will be submitted for publication in international peer reviewed journals in the coming year. We will be completing the pending lipid analyses in the coming months and these will also be submitted for publication in specialized journals.

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