How the Sun contributed to the fall of the Tang dynasty

Science : A 1.2-meter-long chunk of stalagmite from a cave in northern China recorded the waning of Asian monsoon rains that helped bring down the Tang dynasty in 907 C.E., according to Science magazine. A possible culprit, they conclude: a temporary weakening of the sun, which also seems to have contributed to the collapse of Maya civilization in Mesoamerica and the advance of glaciers in the Alps. This latest cave record also points to the potentially devastating effects that climate change--even change that’s mild when averaged around the globe--can have on vulnerable local populations.Paleoclimatologists Pingzhong Zhang of Lanzhou University in China, Hai Cheng of UM, Edwards, and colleagues collected a stalagmite (a mound composed mostly of calcium carbonate slowly precipitated from dripping groundwater) from Wanxiang Cave in northern China at the far reach of the rains of the summer Asian monsoon.Relatively high amounts of uranium and exceptionally low clay-borne thorium in this stalagmite enabled them to conduct uranium-thorium radiometric dating of the layered deposits to within an average of just 2.5 years. As a result, they could calculate precise dates for subtle variations in the stalagmite’s oxygen isotope composition that reflect variations in rainfall near the cave. “They absolutely nailed the rainfall history of [northern] China over the past 1800 years,” says aleoclimatologist Gerald Haug of the Swiss Federal Institute of Technology in Zurich. Related Links Chinese Cave Speaks of a Fickle Sun Bringing Down AncientDynasties A Testof Climate, Sun, and Culture Relationships from an 1810-Year ChineseCave Record