Ancient nomads had a significant hand in the dispersal of the world's oldest domesticated crops, leaving traces in burnt grains of wheat, millet and barley in campsites along the Silk Road, U.S. researchers say.

The evidence has been uncovered from ancient campsites of nomadic sheepherders in high elevation in Kazakhstan dated to 5,000 years ago, a study at Washington University in St. Louis suggests.

"Our findings indicate that ancient nomadic pastoralists were key players in an east-west network that linked innovations and commodities between present-day China and southwest Asia," archaeology Professor Michael Frachetti says.

The finding confirms several varieties of ancient peas and grains were carried across Eurasia many thousands of years earlier than previously believed, the researchers report in the Proceedings of the Royal Society B.

While confirmed as existing much earlier in Southwest Asia and China, the discoveries in Kazakhstan are the earliest evidence of east to west movement of the grains in Eurasia and of farming among by Bronze Age nomadic peoples.

Bread wheat, farmed in southwest Asian more than 6,000 years ago, was not seen in China prior to 2500 B.C., the researchers said. While millet, domesticated in China 8,000 years ago, has left no evidence of its presence in southwest Asia before around 2000 B.C.

But the ancient grains of both regions had arrived in Kazakhstan in the middle of the Asian continent by around 2700-2500 B.C., they said.

"Ancient wheat and broomcorn millet, recovered in nomadic campsites in Kazakhstan, show that prehistoric herders in Central Eurasia had incorporated both regional crops into their economy and rituals nearly 5,000 years ago, pushing back the chronology of interaction along the territory of the 'Silk Road' more than 2,000 years," Frachetti says.

The evidence has been found at four nomadic campsites from the Bronze Age on the steppes and mountains of both Kazakhstan, Tasbas and Begash, also in two sites in Turkmenistan.

"This is one of the first systematic applications of archaeobotany in the region, making the potential for further future discovery very exciting," Washington University researcher Robert Spengler says.

University researchers headed the excavations, working alongside archaeologists from Kazakhstan, Turkmenistan and Italy.

"Finding this diverse crop assemblage at Tasbas and Begash illustrates first evidence for the westward spread of East Asian and Southwest Asian crops eastward, and the surprise is that it is nomads who are the agents of change," Frachetti says.

"It illustrates that nomads had diverse economic systems and were important for reshaping economic spheres more generally."