As far back as 200,000 years ago, Neanderthals were making birch tar, a type of adhesive made from birch bark. Until now, the jury was out on how exactly they made it. Some said it probably happened by accident while burning birch bark, others said Neanderthals actually built subterranean structures just to make the stuff. Well, a new study compared tar recovered from the Neanderthal site of Königsaue in Germany with samples created by the researchers using Stone Age techniques, and they found that tar produced underground contained higher levels of a polymer called suberin. And wouldn’t ya know it, the Königsaue samples were rich in suberin too. They then looked closer and found that the chemical signatures were consistent as well. Because of this, the researchers believe that Neanderthals did indeed use underground chambers in order to restrict oxygen flow — something which obviously required a great deal of knowledge and ingenuity. According to the researchers, “If, however, the Königsaue pieces were made with a method including invisible underground processes and intentionally created low-oxygen environments, such a finding would imply that Neanderthals invented or developed a technical process for transforming their material world. This, in turn, would provide valuable insight into their cognitive and cultural capabilities.” Fun fact: Birch tar is the oldest synthetic substance ever discovered.