BEIJING (AP) — A great flood at the dawn of Chinese civilization was said to have swept away settlements, the water rising so high that it overran hills, mountains and even heaven itself. It was the sage King Yu who tamed the waters by building ditches, the legend went, thus earning a mandate to rule and laying the foundation for China's first dynasty, the Xia.

But until now, scientists could not pin down evidence that the flood, or Yu, or even the Xia Dynasty ever existed outside of the origin myths passed down through millennia.

Now a team of researchers led by Wu Qianlong, a former Peking University seismologist, say in a study published this week in the journal Science that they've indeed found evidence that a flood submerged a vast swath of the country almost 4,000 years ago, possibly lending weight to a longstanding — though controversial — theory that the Xia Dynasty did exist as China's first unified state.

Using radiocarbon dating of juvenile bones and soil samples along the Yellow River, Wu's team established that an earthquake triggered a huge landslide, damming the waterway in 1920 B.C.

The researchers deduced that for six to nine months about 15 trillion liters (4 trillion gallons) of water built up behind a wall of rock and dirt — about half the size of Lake Mead behind Hoover Dam — near Jishi Gorge in today's Qinghai Province. When the dam broke, it tore through the gorge at 500 times the Yellow River's average discharge and submerged the North China Plain that is considered the cradle of Chinese civilization.

The flood would have predated by several centuries the first written records kept on oracle bones. Historical texts from about 1,000 B.C. first mentioned a legendary Xia ruler, Yu, who had devised a system of dredges to control a great flood that spanned generations. He was said to have been based around Jishi Gorge, according to various texts, and his ability to combat natural disasters and earn a heavenly mandate to rule established him as a model for generations of subsequent Chinese rulers.

His legend was later immortalized in some of the best-known historical texts of Chinese antiquity, including the Bamboo Annals of 300 B.C., and the Records of the Grand Historian by the Han Dynasty court official Sima Qian in 94 B.C. But the legend has been hotly debated in modern times.

Over the past century, China scholars have doubted whether the Xia truly existed, or whether it was truly an expansive, unified state rather than simply many smaller states that were mish-mashed together by ancient Chinese political thinkers to justify a tradition of centralized power.

In the 1980s, archaeologists discovered buildings and bronze remains at Erlitou village in Henan Province that were carbon dated to about 1900 B.C. Many scholars believe the settlement, which may have had a population of 30,000, was likely the ancient Xia capital.