Scientists have uncovered the first geological evidence for China's "Great Flood," an event marked in legend as the start of China's first dynasty and the rise of its founding emperor.
The results, reported in the 5 August issue of Science, date the flood at 1920 B.C., several centuries later than suspected. This new timeline suggests that China's first dynasty, Xia — as well as its founding Emperor Yu, famous for controlling the flood — also had a later start.
"The story of Yu taming the Great Flood is also the story of the beginnings of Chinese civilization," said co-author David Cohen, assistant professor in the department of anthropology at National Taiwan University. "Yu's control of the chaotic flood waters brought order to the lands, legend says, separating what would become a civilized Chinese center from the wild peripheries. This defined a people, as well as the social and political order in which they should live. It is central to Chinese identity and known by everyone there, just as Westerners know the story of Noah's flood."
Lead author Wu Qinglong, professor in the department of geography at Nanjing Normal University said the Chinese will consider the findings "a reaffirmation of the core values of being Chinese."
According to Chinese legend, Emperor Yu became famous for his handling of the country's Great Flood. By dredging the Yellow River to increase its carrying capacity, he tamed the destructive floodwaters, "earning him the divine mandate to establish the Xia dynasty … and marking the beginning of Chinese civilization," write Wu and his colleagues.
Yu's story was handed down for a millennium before entering the historical record. Yet, geological evidence for the flood he mastered has been lacking, prompting some scholars to argue "that the story is either a historicized version of an older myth," writes David Montgomery in a related Perspective, "or propaganda to justify the centralized power of imperial rule."
Complicating matters, the existence of the Xia dynasty that Yu heralded has also been debated; in the early 19th century, a group of historians called the "Doubting Antiquity School" arose. "They started to call for scientific proof of the veracity of the historical record in China," explained Wu, "especially the parts recording events before the Qin dynasty in 221 B.C."
By reconstructing a sequence of events along the Yellow River & mdash; including an earthquake-induced landslide that created a dam that later burst — Wu and his colleagues provide geological evidence for a catastrophic flood that may be the basis of the Great Flood.
The work began by accident, Wu said, when he was helping a colleague along the Yellow River in Qinghai Province. There, below a dam, he noticed some unusual sediment — material likely lodged there when the dam broke years before from flooding.
Timelines for the start of the Xia Dynasty vary, depending on the types of evidence used to anchor their dates.| Carla Schaffer/ AAAS
"By identifying those sediments and carefully surveying their locations on both sides of the valley," said co-author Darryl Granger, professor in the department of earth atmospheric planetary sciences at Purdue University, "we were able to determine the dimensions of the flood channel downstream, and exactly how high the floodwaters reached."
Applying these insights in a standard engineering equation, they determined that the flood that broke the dam gushed forth at roughly 300,000 to 500,000 cubic meters per second.
"That's more than 500 times larger than a flood we might expect on the Yellow River from a massive rainfall event," Granger said. "It's among the largest known floods to have happened on Earth during the past 10,000 years."
The researchers dated the massive flood using radiocarbon dating techniques taken from skeletons and sediments found downstream.
"Radiocarbon dating here was a little more complicated than usual because the cataclysmic flood wiped out everything in its path," Granger explained. "Our best dates come from the skeletons of children who were killed in the earthquake just a few months before the flood. Because children's bones grow so rapidly, their radiocarbon age is a true representation of the time that they died."
The date of the children's deaths coincided with the dates for the youngest charcoal found in the flood sediment, Granger explained, pinpointing the date of the flood — and the Xia dynasty to which it is tied — at roughly 1920 B.C.
For archaeologists in China, this date is particularly exciting, Cohen explained. The traditional timeline for establishment of the Xia dynasty is 2200 B.C., according to historians, and it is 2070 B.C. according to the Chinese government's Xia-Shang-Zhou Chronology Project.
"The date of the flood circa 1920 B.C., though," said Cohen, "roughly marks the beginning of the Bronze Age in China. A major transition occurred then, with the appearance of the first bronze ritual vessels and weapons, as well as walled settlements on a scale not seen in the Neolithic. These are the hallmarks of state-level societies in China, which come to appear across the landscape of the Yellow River valley."
This is what scientists would expect to see as the Xia dynasty took root.
Wu hinted at why previous attempts to date the Xia dynasty may have been different. The Xia-Shang-Zhou Chronology Project, for example, based their date on factors including radiocarbon dating of archaeological sites they thought represented the remains of the Xia, when in fact these sites lacked direct proof of this relationship.
Taken together, the results highlight how natural disasters can shape and alter the course of human history. "It is surprising how many seemingly disparate events are actually tied together by the societal response to this major catastrophe," said Wu.
Looking ahead, the team plans to conduct a numerical simulation of the outburst flood on the Yellow River to better understand the possible impacts it had much farther downstream.
"We also plan to study other great floods or mega-floods that we have discovered on the Yarlung Zangbo, Yangtze, and other rivers in China," said Wu.