It's already clear that the ancient Silk Road trafficked in more than spices, grains, and ideas.

Today, more than 150 million people regularly smoke cannabis, making it one of the world's most popular recreational drugs.

But when and where humans began to appreciate the psychoactive properties of weed has been more a matter of speculation than science.

Now, a team led by archaeologists Yang Yimin and Ren Meng of the Chinese Academy of Sciences in Beijing reports clear physical evidence that mourners burned cannabis for its intoxicating fumes on a remote mountain plateau in Central Asia some 2500 years ago.

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Andrew Lawler ~ ScienceMag.org