Archaeologists illuminated a cave with Paleolithic methods

Through a series of experiments, scientists have established the main characteristics of light sources that people of the Upper Paleolithic era could use in caves. Having built a model of illumination for one of the caves with rock art monuments, the researchers showed that Paleolithic man, apparently, used all the light sources available to him – bonfires, torches and lamps based on animal fat. Knowing their advantages and disadvantages, he chose the best lighting method depending on the circumstances.

The study is described in an article in the journal PLoS One.

Deep parts of the caves, in which there is no natural light, were unsuitable for permanent human habitation and never served as dwellings. However, archaeological finds show that the Paleolithic people from ancient times used such caves for ritual purposes. At the earliest stages of the emergence of spiritual culture, primitive burials were apparently arranged in caves, for example, such as in Sima de los Huesos (Spain), where many remains of people of the species Homo heidelbergensis were found, dating back to about 430 thousand years ago. However, the first reliable evidence of deliberate human visitation comes from the Brunickel Cave in southern France. In the depths of it, about 176.5 thousand years ago, the Neanderthals built ring-shaped structures of a ritual nature from the fragments of stalagmites. Traces of fire were found in the cave, for which the bones of animals served as fuel.

The systematic use of deep caves for cult purposes is associated with the activities of the Sapiens in the Upper Paleolithic. And the brightest monuments of the presence of people in the depths of the cave space, where natural sunlight does not fall, could not appear without sufficiently effective lighting. These are numerous examples of rock art and painting. From the Upper Paleolithic era, archaeologists know the traces left by three types of lighting devices: bonfires, torches and grease burners (lamps in which a wick soaked in animal fat burned).

Analysis of the remains of fire sites in Upper Paleolithic caves shows that people used both wood and bone as fuel. Torch marks are recorded in the form of soot on the walls and ceilings, as well as scattered fragments of charcoal. In a number of cases, archaeologists have found (1, 2) the remains of the torches themselves, made of pine or juniper branches. There are also finds of fatty lamps – stones with depressions or fragments of shells, on which there are traces of soot and fat and charred remnants of wicks. These sources are characterized by different intensity of light, and each of them has its own advantages and disadvantages. Upper Paleolithic man could use these features when visiting caves.

Spanish researchers led by Maria Ángeles Medina-Alcaide from the University of Cordoba conducted a series of experiments with all three types of light sources. For the experiments, they chose the Isunza I karst cave in the Basque Mountains in northern Spain. All lighting fixtures were created through reconstruction based on archaeological finds. Scientists measured the duration of burning, the intensity of light, the temperature of the flame, the range of the source and the amount of illumination, and also took into account the degree of smoke that occurs with this or that method.

The researchers made five torches from ivy-tied juniper and birch bark twigs, mixed with pine resin and deer bone marrow. Their burning time ranged from 21 to 61 minutes, and they all smoked quite a lot and gave an uneven flame. However, in order to achieve a more intense combustion, it was enough to wave a torch. The most effective was a torch 55 centimeters long and 11 centimeters thick from carefully dried branches without the addition of resin. It burned longer than others with an average illumination radius of 2.47 meters. The maximum combustion temperature of this torch reached 633 degrees, and the luminous intensity was 10.48 candela. The average illumination at a distance of 40 centimeters was 21.94 lux.

In the experiments, the properties of two lamps on animal fat were also studied, for filling which the scientists used 23 grams of bovine bone marrow. Dried and split juniper branches served as wicks for them. The greases burned at a temperature of about 176 degrees and gave a weak (on average 0.59 candela) light in a radius of 1.57 meters. At 40 centimeters from the flame, the average illumination was 3.71 lux. Despite their weakness, these lamps have important advantages: they burn for a long time (more than an hour) and practically do not produce smoke.

An experimental bonfire measuring 23 centimeters, built of oak and juniper branches with the addition of birch bark, burned at a temperature of about 587 degrees and gave an uneven flame with an average illumination radius of 3.3 meters and a maximum of up to 4.5 meters. However, at a distance of more than two meters, the illumination values ​​turned out to be close to zero. The average luminous intensity produced by the fire was about three candelas, and the illumination of 40 centimeters was 19.2 lux. Due to the lack of ventilation, the smoke in the part of the cave where the fire was made was very strong, and after 30 minutes the researchers stopped the experiment. This shows how important it was to select a well-ventilated cave site for the campfire.

Based on these results, Medina Alcaide and her colleagues simulated lighting options for the Achurra Cave in the same area. It contains images of animals – bison, horses, deer – belonging to the Late Paleolithic Madeleine culture, which was widespread in Western and Central Europe 17000-12000 years ago. Under the engraved cave paintings on a massive stone ledge 2.5 meters high, there are traces of three fireplaces, charcoal particles were found in various places of Achurra, and a stone lamp from this cave served as a model for experimental firemen.

Simulations showed that the images on the wall were nearly impossible to see if any light source was below the rock ledge – even taking into account the reflection of light from the walls of the underground gallery. The location of the bonfires on the ledge was not accidental: the bonfires burning there not only made it possible to see the drawings, but made the entire surface of the decorated wall accessible for viewing. The scattered fragments of coal were apparently left behind after moving with torches. It takes about 40 minutes to reach this section of the cave, and researchers believe that two juniper torches were enough to provide a way back and forth. However, it is likely that when going into the cave, people took spare grease and torches. Why fat lamps were used in Achurra is still unclear. They may have been used to create images or complement the lighting created by bonfires.

The results of the experiment also allow one to imagine what the rock paintings looked like to the visitors of the cave. With any of the studied light sources, the so-called mesopic, or twilight, vision is activated. It is less associated with color sensitivity than daytime, and more with the perception of contrast between illuminated and unlit areas. At the same time, the rays of the long-wavelength parts of the spectrum – yellow, orange and red – emitted by the flame of a fire, torch or lamp are more clearly perceived. In Achurra, the engravings are black, but in other caves, ocher pigments were often used for painting, which appeared more saturated under these lighting conditions. According to scientists, the features of twilight vision associated with the selectivity of color perception and increased sensitivity to the play of light and shadow played a large role in rituals inside the space of the caves.

Analysis by Spanish scientists shows that people in the Upper Paleolithic era could purposefully apply light sources with different characteristics, knew about the properties of available combustible materials and used the morphology of caves to achieve optimal results. They knew how to make quite complex lighting devices that made it possible to penetrate far into the depths of the caves and stay there for a long time. The authors of the article plan to conduct research on more material in the future and extend the modeling to caves with different profiles and arrangement of drawings.

Earlier, archaeologists talked about the oldest rock carvings of an animal found in a cave on the Indonesian island of Sulawesi, explained why climate change entails the destruction of this most valuable monument, and also reported the discovery of the first evidence of a Paleolithic man hunting a small cave bear.