The team identified the chemical traces clinging to the burners using a technique that articulates a sample’s chemical signature. By vaporizing the sample, separating its components, and recording their differences in mass, researchers can identify the relative levels of the chemicals they’re looking at. “To our excitement, we identified the biomarkers of cannabis,” says Yimin Yang, another co-author of the study and a researcher at the University of the Chinese Academy of Sciences. And not just cannabis, but a strain bursting with CBN, the compound that forms after THC metabolizes. (These Jirzankal Cemetery samples contained, however, noticeably low levels of CBD—a medicinal, nonpsychoactive compound favored by some cannabis users.) Higher than what are typically found in regional, wild cannabis plants, the CBN levels suggest that the ancient grave keepers deliberately sought out these mind-altering varieties, and potentially even domesticated them.
Those elevated levels are what make this discovery so exciting and unique next to other confirmed examples of ancient cannabis, according to Mark Merlin, a professor of botany at the University of Hawaii at Mānoa. With those findings, says Merlin, a co-author of Cannabis: Evolution and Ethnobotany, determining the cannabis’s function was harder, as the samples weren’t so clearly tilted toward the psychoactive end of the spectrum. These results, meanwhile, are rather more persuasive, and suggest that ancient humans were lighting up to honor the dead long before that became a stoner’s cliché.
The excavations dug up more than just THC residue. Notably, analysis of human bones found at Jirzankal revealed that not all of the cemetery’s tenants had been born locally. This hint of ancient immigration supports the idea that the high-elevation Pamirs were once part of the Silk Road, along which goods and traditions passed between geographically distant communities. Spengler told reporters that these findings suggest that cannabis, and ideas regarding its various uses, may well have been among the items exchanged along the Silk Road. Another discovery supporting this idea—a grave in northwestern China laid with large cannabis plants—was described in 2016 by the archaeologist Hongen Jiang, another co-author of the new paper.
This new investigation of ancient cannabis use, says Patrick E. McGovern, the scientific director of the Biomolecular Archaeology Project at the Penn Museum, “is a much-needed contribution to our scientific understanding of the vast expanse of central Asia—some 4,000 miles from the Caucasus Mountains through the Pamirs and across the forbidding Taklamakan Desert. It provides yet another piece in the archaeological puzzle of the ‘abiding mystery of Central Asia’ and its impact on human cultural and biological development through the millennia.” But much more remains to be learned about the ways cannabis might have been used (perhaps as a medical additive or in fermented beverages) and the ways ideas about fermentation and the related domestication of plants moved across this area, without leaving their trace on artifacts. “We are still very much in the dark about the underlying dynamics of the transfer of fermented beverages and their mind-altering additives”—including cannabis—“from oasis to oasis along the prehistoric Silk Road and back into the Central Asian hinterland,” McGovern wrote in his book Uncorking the Past.