An international team of researchers, including Hebrew University of Jerusalem’s Dr. Liora Kolska Horwitz, has found evidence of the earliest use of fire in the Wonderwerk Cave in South Africa, with findings published this month in the PLOS ONE journal. The discovery pushes the origin of intentional use of fire back by several hundred thousand years, to as early as 1.8 million years ago, after previous research in 2012 dated evidence from a more superficial level of the same cave to one million years ago.
Who Controlled the Timeline
The new date comes from a deeper layer in a cave whose long record has been studied for years by researchers using specialized methods and institutional backing. Kolska Horwitz, co-director of the Wonderwerk Cave project with Prof. Michael Chazan of the University of Toronto, said the team developed an innovative technique to detect signs of burns on fossilized bones. She said: “In 2012, when we published the article about the Wonderwerk Cave at one million years ago, we had the indications that there was fire in a lower, older level. Now, we pushed the use of fire back to well over a million years ago.” She said the two levels are separated by around 80 centimeters of sediments.
The deeper level was in use between circa 1.79 and 1.079 million years ago. Kolska Horwitz said: “The sample we use for this study was close to the bottom, and therefore to the 1.8 million years ago period.” The evidence that fire was used does not mean early humans were the ones igniting it, but the fact that it was found deep inside the cave suggests it did not reach that depth naturally and was brought there on purpose.
Kolska Horwitz said: “This is intentional use of fire, which doesn’t mean that people started it; they are two separate things.” She added: “We can say that it’s not a natural fire, because the fire is at least 30 meters in from the entrance of the cave, so it was not a wildfire that crept in. There is also nothing in this layer that could have caused what we call spontaneous combustion, like guano [accumulation of animal excrement] that suddenly burns by itself due to the chemical composition. The fire must have been introduced there by someone.”
What the Cave Holds
Kolska Horwitz has been working at Wonderwerk for over 20 years. She said the site is unique because humans lived in the cave for two million years, from the earliest known occupants to a farmer’s family that temporarily sheltered there in the early 20th century. “The cave occupation begins at about two million years and is associated with a stone tool culture called the Oldowan,” she said. “Most Oldowan sites were little campsites in the open air. Here we have a cave where people intentionally moved in, so Wonderwerk is the oldest cave home.” She said the cave features stone tools from all the different phases of occupation and that the long record at one site allows researchers to follow the evolution of technology. She also said people hunted or scavenged animals, so the site contains the remains of the animals they ate.
One thing never found in any level of the cave was human bones, so the scholars cannot say for certain what kind of early humans lived there, including those associated with the earliest use of fire. Kolska Horwitz said: “There were several hominins in southern Africa at that time, and since we haven’t found any human remains, it is a bit difficult to pin [which type lived in the cave] with any certainty, but likely it was a form of Homo erectus.” She said: “Perhaps it is going to happen when we go back to excavate in July.”
According to Kolska Horwitz, the method for detecting burns on bones developed by the PLOS ONE study authors opens new possibilities for searching for traces of fires across prehistoric sites and remains worldwide. She said: “The new method uses luminescence [to detect] signs of burning.” She said the reason for developing a new method was that standard ones are expensive and invasive because they require grinding up a small piece of bone and destroying evidence. “The idea was to develop a method that’s quick, cheap, and can also be run by people working in the field in a small field station,” she said.
The technique entails applying a substance to the bone, waiting for it to react, and examining the bone under UV light, where the burnt areas glow white. Kolska Horwitz said the team hopes other researchers around the world will adopt the method, which could lead to additional evidence of the use of fire in early prehistoric times.
The dating of the site was carried out in previous years mainly by an Israeli team from the Hebrew University, including Kolska Horwitz, and the Geological Survey of Israel. First, the scientists used paleomagnetic dating, which relies on changes in Earth’s magnetic field as magnetic north shifted over the millennia. Kolska Horwitz said: “It’s a standard method used in Earth sciences. We used the sediments in the cave to get a signal of the magnetic directionality.” The second type of analysis was cosmogenic burial dating. Kolska Horwitz said: “This is also based on sediments in the cave. When the soil entered the cave, little white quartz grains from the sand found in the soil stopped receiving radiation from the sun’s cosmic rays, and locked. In the laboratory, we can [analyze] that signature that tells us when the sediment entered the cave.” Now that they have proved fire was used close to 1.8 million years ago, the archaeologists plan to check for evidence of it even in the deepest level of the cave’s occupation, dating to two million years ago. Kolska Horwitz said: “This is the big question now.”