Making adhesive: how on earth did the Neanderthals do that?

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Making adhesive: how on earth did the Neanderthals do that?

Three different methods discovered, from simple to complex

Neanderthals were already making adhesive out of birch bark tar 200,000 years ago. But how on earth did they do it? Archaeologists from Leiden University have demonstrated that Neanderthals were able to extract useable amounts of tar from birch bark, albeit basically through trial and error. Controlling the temperature turned out not to be nearly as important as what had been thought up until now.

We knew that Neanderthals were able to make tar. But archaeologists thought they used technically advanced methods where a temperature between 340 and 370 degrees Celsius had to be maintained. Research from Leiden researchers Kozowyk, Soressi, Pomstra and Langejans has now shown that strict temperature control is not necessary to keep the production at an acceptable level of usability. And that is new.

Nature Scientific Reports published an article on the subject this this week written by, among others, experimental archaeologists Paul Kozowyk (PhD student at ARCHON Research School of Archeology) and Geeske Langejans (Talent Scheme Veni): ‘Experimental methods for the Palaeolithic dry distillation of birch bark: implications for the origin and development of Neanderthal adhesive technology’.

Replicated flint point attached to a wooden haft with birch bark tar.Replicated flint point attached to a wooden haft with birch bark tar. Credit D. Pomstra

Why did humans from the Early Stone Age use birch bark tar? The substance was found to be a huge improvement in, for example, fixing a spearhead to a spear. Compared with previous technology using animal ligaments, tar made it possible to create a more seamless connection. Applying birch tar allowed the arrowhead to be mounted very solidly. Axes and other hacking and scraping tools that connected wood with stone or bone rose in quality thanks to the use of tar.

Drops of sticky material

Paul Kozowyk: “You mustn't think that 200 millennia ago ‘someone’ suddenly had this fantastic idea: you know what, from now on we’re going to do it like this. Nope, people just saw the various aspects of assembling tools that didn’t work well. There was an abundance of birch trees: usually good firewood and the bark makes great tinder. The birch bark rolls up automatically as soon as it's pulled from the tree. They saw drops of sticky material forming between the rolled-up layers of bark in the fire that could be used as adhesive. Little by little a constant need for such materials arose. But that took tens of thousands of years.”

Dripping glue.Dripping glue. Credit P. Kozowyk

Bits of 200,000-year-old tar adhesives were found at an archaeology site in Campitello, Italy, just south of Florence. The discovery is considered to be proof of the first ‘transformation technologies’ that the earliest humans developed. This type of technology entails a complete transformation of the ingredients; for example, like baking a cake; the cake can never be changed back into eggs, butter, flower and sugar. By manipulating the birch bark in such a specific manner an entirely new material was created.

Did you know? Other than Campitello there is only one other place in Europe (Königsaue in Germany) with simmular amounts of adhesive

Intact adhesives from such a distant era are extremely rare. Other than Campitello there is only one other place in Europe (Königsaue in Germany) with chemically identified macroscopic amounts of adhesive and there is no direct archaeological proof of how it was made.

Geeske Langejans: “In such situations, experimental archaeology offers a glimpse of Neanderthal technology. Our Neanderthal ancestors from the Early Stone Age heated birch bark, without oxygen to prevent incineration, to create sticky black tar. To gain a better understanding of this discovery we only used materials and techniques that were available in the Stone Age in this experimental study: birch bark and fire. And we used our common sense as to what the Neanderthals might have done.”

Tar yield from pit roll method in bark container.Tar yield from pit roll method in bark container. Credit P. Kozowyk

Earlier attempts by other researchers to experiment with making birch bark tar with the help of non-ceramic technology (in other words: without pottery –editor) only yielded tiny amounts of tar or something else went wrong. So it was assumed that producing tar was very difficult, in particular controlling the temperature. Paul Kozowyk: “We’ve demonstrated that there's more than one way to make tar and that each method also worked with large temperature variations. In a nutshell: tar is produced at 300 degrees Celsius, but also at 600 degrees Celsius. That means that Neanderthals didn’t have to work as precisely as we had thought.”

There's more than one way to make tar. Each method worked with large temperature variations.
- Paul Kozowyk

In an experimental setting in Zeewolde, in a reconstructed house of the first Dutch farmers, researchers Kozowyk and Langejans used a variety of heating, scorching and collecting techniques to see what worked best. They also weighed and measured all the variables, such as the kilos of firewood, the temperature of the fire and the birch bark, the amount of birch bark and the local wind speed. Various methods were found to work. Some are really simple and you don’t really need anything other than a roll of birch bark and a couple of pieces of glowing hot charcoal. Other methods are more complex and involved containers, dug-out pits and small earthen ovens.

Langejans: “It’s not unthinkable that a Neanderthal used a different method when maintaining his weapons and tools than when he was out hunting and needed to repair a few spears. The more complex the method, the higher the yield but our most important discovery was that temperature is in no way a showstopper. The precise control of heat was apparently unnecessary.”

More information

 

Underground tar production in time lapse on Youtube

Underground tar production in time lapse on Youtube.

Tar production with a raised structure in time lapse on Youtube

Tar production with a raised structure in time lapse on Youtube.