Pech-de-l’Azé (France):Neandertals may have used chemistry to start fires

Lizzie Wade

Source - http://www.sciencemag.org/news/2016/02/neandertals-may-have-used-chemistry-start-fires?

Scientists know a lot about Neandertals these days, from their hair color to their mating habits. Still, a basic mystery remains: Did they know how to start a fire? Archaeologists have long known that Neandertals used fire, but they could have merely taken advantage of naturally occurring lightning strikes and forest fires to supply the flames. Now, a new hypothesis about some odd Neandertal artifacts suggests that our distant cousins could indeed spark a fire from scratch. Excavations at the 50,000-year-old site Pech-de-l’Azé I in southwestern France have yielded blocks of manganese dioxide, which is abundant in the region’s limestone formations.

Archaeologists previously thought that Neandertals used the substance as a black pigment to decorate their bodies. But a new team of researchers points out that charcoal and soot from their campfires would have made for easier and more accessible body paint. Plus, the Neandertals at Pech-de-l’Azé I appeared to have strongly preferred manganese dioxides to the other manganese oxides available in their environment, even though all of the closely related chemicals would have yielded the same color pigment. So what can manganese dioxide do that its relatives can’t? Start fires. Noticing signs of abrasion on some of the Pech-de-l’Azé I blocks, the scientists ground up bits of them to produce a powder. When they sprinkled that powder on a pile of wood, it lowered the temperature needed to initiate combustion to 250°C, making it much easier to start a fire, they report today in Scientific Reports. (Untreated wood failed to ignite at temperatures up to 350°C.) The researchers can’t rule out other possible Neandertal uses for manganese dioxide, including body decoration. But based on their experiments, they suggest adding fire-starting to the list.

Selection and Use of Manganese Dioxide by Neanderthals

Scientific Reports 6, Article number: 22159 (2016) doi:10.1038/srep22159

http://www.nature.com/articles/srep22159#f2

Abstract

Several Mousterian sites in France have yielded large numbers of small black blocs. The usual interpretation is that these ‘manganese oxides’ were collected for their colouring properties and used in body decoration, potentially for symbolic expression. Neanderthals habitually used fire and if they needed black material for decoration, soot and charcoal were readily available, whereas obtaining manganese oxides would have incurred considerably higher costs. Compositional analyses lead us to infer that late Neanderthals at Pech-de-l’Azé I were deliberately selecting manganese dioxide. Combustion experiments and thermo-gravimetric measurements demonstrate that manganese dioxide reduces wood’s auto-ignition temperature and substantially increases the rate of char combustion, leading us to conclude that the most beneficial use for manganese dioxide was in fire-making. With archaeological evidence for fire places and the conversion of the manganese dioxide to powder, we argue that Neanderthals at Pech-de-l’Azé I used manganese dioxide in fire-making and produced fire on demand.

Figure 1: Blocs from Pech-de-l’Azé I - both unmodified (b,d) and with abrasion marks (a,c). (b) is MD3 from the excavation spoil of early 20th century excavations and the others were recovered in the 2004 and 2005 field work campaigns.

Figure 2: Combustion Experiments with Manganese Dioxide MD4 and Wood Mixtures (a) showing small red flames and volatile emission and (b) the glowing fire combustion phase.