A 65,000-Year-Old Hearth Reveals Evidence That Neanderthals Produced Tar for Stone Tools in Iberia

When fire was invented, it changed the course of human evolution. It provided warmth, enabled cooking and facilitated the creation of more advanced tools. For instance, one pivotal tool, the stone-tipped spear, might have been assembled using tar and other adhesives. While early tar production remains largely a mystery, scientists have now uncovered a 65,000-year-old hearth that appears to have functioned as a small-scale “tar factory.”

In a new study published in Quaternary Science Reviews in November, scientists describe a 65,000-year-old hearth found in Gibraltar on the Iberian Peninsula. The fire pit was theoretically used to make tar—and if that conclusion is proven true, it also represents the first evidence of the use of the plant rockrose, Cistus ladanifer, for obtaining tar.

“For this reason, it can be said that it was unexpected,” says Juan Ochando, lead author of the study and a biologist at the University of Murcia in Spain, to Discover magazine’s Paul Smaglik.

Scientists already knew that Neanderthals made adhesives using other materials like ocher and naturally sticky substances to haft stone tips onto wooden shafts to create weapons. The newly described hearth in Gibraltar represents a “specialized burning structure” for tar production, the researchers write in the study.

“Stone Age adhesives are an important and still much understudied aspect of early humans,” says Patrick Schmidt, an archaeologist at the University of Tübingen in Germany who was not involved with the study, to Science’s Taylor Mitchell Brown.

Still, Schmidt says that although the study points to wood burning in the hearth, more evidence is needed to conclude for certain that Neanderthals used the hearth to make tar.

The ancient hearth was uncovered in the Vanguard Cave, part of the Gorham’s Cave Complex, a UNESCO World Heritage Site in Gibraltar. This area is renowned for its rich history of Neanderthal findings, including tools and cave art. Research in the Vanguard Cave began in 2012, and since then, scientists have revealed several new findings in its passageways and chambers.

One such discovery was a cave chamber full of ancient hearths and stone tools dating to the time of Neanderthals, uncovered in 2021 by Clive Finlayson, an evolutionary biologist and director of the Gibraltar National Museum. He told the Guardian’s Sam Jones at the time that the “caves have been giving us a great deal of information about the behavior of these people.”

That remains true today with the discovery of the prehistoric hearth, where researchers found charcoal and remnants of the rockrose plant. Chemical analysis of the hearth’s contents revealed burning residues and traces of wax from leaves, suggesting the controlled use of fire—and possibly the production of tar. The team also found guano, or bat and bird poop, in the hearth. They suggest Neanderthals used guano with a mix of sand to cover the plant materials, allowing them to heat up and melt without fully catching fire.

To prove it is possible to produce a significant amount of tar from rockrose resin, Ochando and his team set out to make a similar hearth. They intended to do so with materials and techniques that would’ve been available to Neanderthals in the area at the time.

First, they filled their replica hearth with rockrose leaves, then covered them with sand and soil. They built a small fire with grass and rockrose wood and let it burn for two hours. Afterward, the result was a mixture of rockrose leaves dripping with labdanum, a sticky resin, that the scientists used to haft arrowheads to wood in a type of makeshift spear.

For Neanderthals, this effort might have been a cooperative process, as study co-author Francisco Jiménez-Espejo, a scientist at the Andalusian Earth Sciences Institute in Spain, tells Live Science’s Kiona Smith. On either side of the hearth, the researchers found a pair of straight furrows cut in the ground, where he suggests two Neanderthals might have dug into the hearth to remove the hot leaves from opposite sides. Separating the tar from the leaves is much harder when the leaves have cooled, so they had to work quickly, he adds.

Although this production of tar will require further study, Ochando says the work aligns with the current suppositions about tar production. As he tells Science, Ochando hopes the findings “may serve as a starting point for other researchers when identifying these structures in other archaeological sites.”

Alexa Robles-Gil | | READ MORE

Alexa Robles-Gil is a bilingual science journalist based in New York City. Her work has appeared in the Guardian, Undark, Inside Climate News and more.