The origin of marijuana has finally been discovered and it dates back 28 million years to the Tibetan plateau, 10,700ft (3km) above sea level.
Researchers analysed pollen fossils of the plant and found it slowly dispersed over millennia to Europe, China and India.
It has long been known cannabis originated in Central Asia but its exact location had remained a mystery until now.
Archaeological evidence of its use as a drug dates back to to 2,700 BC in the nearby Xinjiang region north west of China.
Scroll down for video
The origins of the cannabis plant has finally been traced to an area of the Tibetan plateau (pictured) 15, 000ft (3km) above sea level
A team of researchers led by the University of Vermont in the US examined 155 existing fossil pollen studies from Asia in order to ‘to reconstruct the evolutionary and human related history of Cannabis in Asia’, said the authors in the report.
By looking at genetic analysis and fossils of cannabis pollen, they pinpointed the origins of its growth to 28 million years ago to the area of Qinghai lake on the Tibetan plateau.
They mapped the fossil data and found the oldest pollen fossil dates to 19.6 millions BC where it was likely cultivated by humans, given that both hem crop and fruits seeds fossils were also found at archaeological sites.
The plateau in the southwest of China measures 14,800 ft (4,500 m) above sea level at its peak and the lake sits at 10,700ft (3km) up the range.
The area overlaps with the first hunter and gatherer community that evolved in Asia, although no link has been made between the two.
Based on their analysis, the researchers found evidence the cannabis strain of hemp first disseminated to Europe and then East to China followed by India due to tectonic movements in the Earth that caused land mass to move closer to each other.
WHERE IS THE TIBETAN PLATEAU?
Also called Tibetan Highlands or Qinghai-Tibet Plateau, it is a vast high plateau of southwestern China.
It encompasses all of the Tibet Autonomous Region and much of Qinghai province and extends into western Sichuan province and southern Uygur Autonomous Region of Xinjiang.
It has an area of about 965,000 square miles (2,500,000 square km), is a region of tangled mountains and uplands that are generally above 13,000 to 15,000 feet (4,000 to 5,000 metres) in elevation.
Lhasa, the capital of Tibet, is the plateau’s major centre of population, economic activity, culture, and air and land transportation.
The flowering tops of cannabis strains such as hemp plant produce cannabinoids, which have been used to make the cannabis drug.
One reason the origins of the plant have been so hard to trace is because the leaves of cannabis plants – such as hemp – don’t create very good print fossils, and only two collections of the plant fossil exist.
In contrast, hundreds of pollen fossils have been found and analysed, which the current study reviewed.
While widely known as a drug, the cannabis plant in fact had may functions for communities that used its plant fibres, for providing cordage and textiles, for example.
Carbonised hemp fibres, found with silk and spinning wheels, date to 5,600 BC, in Henan Province, China.
Researchers analysed studies of pollen fossils from the plant and showed that it disseminated over the millennia to Europe, China and then India.
It has long been known the plant originated in Central Asia but its exact location on the Tibetan plateau around Qinghai Lake (shown on map) had remained a mystery
Scientists also put down the appearance of cannabis elsewhere in the world down to tectonic movements of the earth, rather than humans migrating with it.
The researchers wrote: ‘Early floristic exchanges between India and Asia were shaped by plate tectonics,’ the researchers wrote in their paper.
‘As the Indian plate migrated towards the Asian plate, it made a ‘glancing contact’ with Sumatra 57 [million years ago], followed by Burma, and then a ‘hard collision’ with Tibet 35 [million years ago].
‘The glancing contact between continents resulted in floristic exchanges during the Eocene.’
‘Cannabis holds significance in human history and life today as a triple-use crop. First, its fruits (seeds) provide valuable protein and essential fatty acids’, wrote the researchers.
Archaeological evidence in a food context dates back to 10,000 BC in Japan.
The full report was published in the journal Vegetation History and Archaeobotany.