Drastic Aridification Caused the Decline of Oasis Civilizations on the Silk Route during the Eighth Century

Availability of water, and response to shortage of it, plays an important role in shaping human history. Near a century ago, Ellsworth Huntington (1907) suggested that the developments of ancient civilizations in Inner Asian and their invasions into China and Europe were pulsed by climatic changes. In revisiting this proposition, here we present a paleoclimatic record of the past 5000 years deduced from carbon isotopic ratio of organic carbon and percentage of aragonite in bulk sediments of a radiometrically dated sedimentary core of Lake Bosten, Xinjiang, China. Together the two proxies of aridity provide a detailed record of climatic fluctuation of the Inner Asia. The arid periods are well characterized by high content of authigenic aragonite and heavier values of carbon isotopic ratio of organic carbon in the bulk sediments (implying dominance of C4 plants which thrived under arid condition). Conversely, the humid/wet periods are marked by lighter carbon isotopic values (indicating presence of C3 plants of humid climateœcand absence of aragonite. The Western Region (Xi-Y"1) area of China enjoyed a long period of stable and humid condition from 2nd century B.C. to the 8th century when many oasis city-states were established and Buddhism spread from India. A drastic deterioration of climate during the eighth century appears to cause the decline of those once strived ancient civilizations in the eastern side of the Tarim Basin along the Silk Routes.