(CNN)Cannabis has been cultivated as a crop for millennia, but there's been little historical or archeological evidence showing when humans began to use the plant for what it's best known for today: getting high.
2,500-year-old tomb offers earliest evidence of humans using cannabis to get high
However, an excavation of a 2,500-year-old tomb in western China has revealed the earliest clear evidence of humans using cannabis for its psychoactive properties.
Scientists from China and Germany analyzed wooden fragments and burnt stones from pots in the tombs, and the results showed an exact match to the chemical signature of cannabis -- particularly that with a high amount of tetrahydrocannabinol (THC), the most potent psychoactive agent in the plant.
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.
However, it was unlikely that cannabis was smoked in the same way it is today. More likely, it would have been burnt like incense in an enclosed space to release vapors.
Nicole Boivin, director of the Max Planck Institute for the Science of Human History and an author of the report, said the cannabis was burned on hot stones inside wooden braziers, containers for hot coals.
"This is the only way that cannabis could have been smoked prior to the arrival of pipe technology, which is not until much later, it seems," she said.
The 10 braziers were found in the Jirzankal cemetery in the Pamir Mountains near the Chinese border with Pakistan.
It had long been a mystery when and where varieties of cannabis plants with higher levels of psychoactive compounds were recognized and used by humans, according to the study.
Cannabis plants were cultivated in East Asia for their oily seeds and fiber from at least 4000 BC. However, the early varieties of cannabis, as well as most wild populations, had low levels of THC and other compounds with psychoactive properties, the authors said.