Marijuana can linger in the human system for a few months at most, but cannabis residue will stick to other surfaces for millennia. High up in the Pamir Mountains, in what is now western China, archaeologists were excavating the tombs of Jirzankal Cemetery when they came upon a set of braziers and asked themselves what purpose the tools served. After analyzing the residue, a team of researchers found that it not only came from cannabis, but contained unusually high levels of THC—the compound that gives cannabis its psychoactive, or mind-altering, qualities.
“To our excitement we identified the biomarkers of cannabis, notably chemicals related to the psychoactive properties of the plant,” said Yimin Yang at the University of Chinese Academy of Sciences in Beijing. Specifically, the scientists found cannabinol, a substance produced when THC is oxidised. Given the lack of other cannabis breakdown products, the scientists believe the plants were selected to be high in THC, but whether they were cultivated or found in the wild is unclear.
“Modern perspectives on cannabis vary tremendously cross-culturally, but it is clear that the plant has a long history of human use, medicinally, ritually and recreationally over countless millennia,” said Robert Spengler, an archaeobotanist at the Max Planck Institute for the Science of Human History in Jena, Germany, who worked on the study.
The authors of the study, which was published Wednesday in journal Science Advances, suggested that cannabis was probably used during burial ceremonies, perhaps as a way to communicate with the divine or the dead.
Cannabis stems and seeds had previously been found at a handful of burial sites around Eurasia, but the evidence at the Pamir cemetery, verified by advanced scientific technology, shows an even more direct connection between the plant and early ritual. The new findings expand the geographical range of cannabis use within the broader Central Asian region, said Mark Merlin, a professor of botany at the University of Hawaii at Manoa, who did not work on the research.
The authors said that cannabis plants produce greater quantities of active compounds when they grow at higher elevations, and this may be why more potent plants had been discovered — and a new use initiated — by people living in high mountainous regions like the Pamirs.
Dr. Merlin said that the Pamir cemetery, together with other relatively contemporaneous burial sites elsewhere in the Xinjiang region of China, strengthens a striking narrative about how cannabis was used ritually by local cultures. North of the Pamir cemetery and from roughly the same period, other researchers identified a container with about two pounds of chopped cannabis next to the head of a body believed to be a shaman, presumably to use for herbalist concoctions in the afterlife.
At yet another grave, also about 2,400 to 2,800 years old, in the dry desert of Xinjiang, researchers recently discovered a man about six feet tall buried with “13 cannabis plants gathered at their base and spread across his breast like a bouquet of roses,” Dr. Merlin said.The array has also been described as a “cannabis shroud.”
“Modern perspectives on cannabis vary tremendously cross-culturally, but it is clear that the plant has a long history of human use, medicinally, ritually, and recreationally, over countless millennia,” Spengler added.