In the Yangtze Delta, about 160 kilometers southwest of Shanghai, lie the archaeological ruins of the city of Liangzhu. A highly advanced culture flourished there around 5,300 years ago, thanks to the construction of large hydraulic structures.
The fortified city had a complex system of navigable canals, dams and water reservoirs. This system made it possible to cultivate very large agricultural areas throughout the year. In the history of human civilization, it is one of the first examples of highly developed societies based on a water infrastructure.
And they did it all without metal.
Long undiscovered, the archaeological site is now considered a well-preserved record of Chinese civilization dating back more than 5,000 years and was declared a UNESCO World Heritage Site in 2019. However, the advanced civilization of this city came to an abrupt end.
“A thin layer of clay was found on the preserved ruins, which points to a possible connection between the demise of the advanced civilization and flooding from the Yangtze River or flooding from the East China Sea. No evidence could be found for human causes such as war-like conflicts,” explains Christoph Spötl of the University of Innsbruck.
The stalactites of Shennong Cave (pictured) and Jiulong Cave provide an accurate insight into the time when the Liangzhu culture collapsed around 4,300 years ago. Credit: Haiwei Zhang
Stalactite stores the answer
Caves and their deposits, such as stalactites, are among the most important climate archives that exist. They allow the reconstruction of climatic conditions over the caves up to several 100,000 years back in time. Since it is still not clear what caused the sudden collapse of the Liangzhu culture, the research team searched for appropriate archives to investigate a possible climatic cause of this collapse.
Geologist Haiwei Zhang from Xi’an Jiaotong University in Xi’an took samples of stalagmites from the two caves of Shennong and Jiulong, which are located southwest of the excavation site.
Data from the stalagmites show that there was a period of extremely high rainfall between 4345 and 4324 years ago. Evidence for this was provided by isotopic records of carbon, which were measured at the University of Innsbruck. The precise dating was done by uranium-thorium analyzes at Xi’an Jiaotong University, whose measurement accuracy is ± 30 years.
The massive monsoon rains probably caused such heavy flooding of the Yangtze and its branches that even the sophisticated dams and canals could no longer withstand these masses of water, destroying Liangzhu City and forcing people to flee. The very humid climatic conditions continued at regular intervals for another 300 years, as the geologists show from the cave data.
Citation: Haiwei Zhang, Hai Cheng, Ashish Sinha, Christoph Spötl, Yanjun Cai et al. Collapse of Liangzhu and other Neolithic cultures in the lower Yangtze region in response to climate change. Sci. Adv.2021 DOI: 10.1126/sciadv.abi9275
