Researchers may have found the answer to the mystery of how early hominids processed tar as an adhesive.
In 2005, a discovery by a team of palaeontologists in Italy brought two challenging questions into sharp focus.
A team led by Paul Mazza of the University of Florence were investigating a quarry pit in the north of the country when they discovered some stone flakes – clearly cutting blades – near the ancient bones of mice and a small elephant.
The condition of the animal remains allowed the scientists to date the remains with confidence to the Middle Pleistocene period – 781,000 to 126,000 years ago.
The stone flakes themselves were covered in a black sticky substance, a form of tar made from birch bark. This narrowed the age range of the artefacts to not before 200,000 years ago – from which the earliest recorded tar findings date.
These deductions underlined a matter that had intrigued palaeoarchaeologists for quite some time: how did early humans manage to make tar – used as adhesive to fix handles to stone cutting blades – given that the process requires sophisticated time and temperature management. In short, how did they manage to make it without ceramics?
The date of the Italian tar-smudged rocks, however, threw up an even more intriguing question. In the possible date range for their manufacture, Homo sapiens were not present in the region. Neanderthals were, however.
Evidently, Neanderthals had worked out a technology for tar manufacture that did not involve the use of ceramics – something that until very recently modern humans have failed to do. The discovery also prompted a new set of speculations about the cognitive abilities of the hominid species. Before one can make tar, after all, one first has to imagine it – and imagine a use for it.
Now, however, research by a team led by Paul Kozowyk of Leiden University in the Netherlands might just have found an answer, at least to the first question.
In a paper published in the journal Scientific Reports, Kozowyk and colleagues report using three methods to try to produce tar from the destructive “dry distillation” of birch bark. All three, ranked in increasing levels of complexity, used technologies that were available during the Middle Pleistocene.
The most successful involved digging a pit into which a birch bark container was placed. The pit was then covered with a makeshift organic mesh onto which was placed some loose sheets of bark. This was then covered with earth, and a fire below it.
“This method resulted in the most variable output of tar, but when successful it gave the highest yields by a large margin,” the scientists report.
On their best attempt, the researchers used the structure to generate almost 16 grams of tar from 100 grams of bark. It became clear that repeating the process several times would easily produce the amounts of tar needed to haft tools of the type found at Neanderthal excavation sites.
Kozowyk and his colleagues also found that, contrary to expectations, making birch bark tar by using fire, earth and ashes is a quite a forgiving processes.
“A ceramic container is not required, and temperature control need not be as precise as previously thought,” they write.
The development and employment of tar in tool-making, however, implies a significant level of intelligence in its makers.
“Neanderthals must have been able to recognise certain material properties, such as adhesive tack and viscosity,” the scientists conclude.
“In this way, they could develop the technology from producing small traces of tar on partially burned bark to techniques capable of manufacturing quantities of tar equal to those found in the Middle Paleolithic archaeological record.”