Ancient Cave Sheds Light on China's Past

Nov. 6, 2008 -- A stalagmite rising from the floor of a cave in China is providing clues to the end of several dynasties in Chinese history.

Slowly built from the minerals in dripping water over 1,810 years, chemicals in the stone tell a tale of strong and weak cycles of the monsoon, the life-giving rains that water crops to feed millions of people.

Dry periods coincided with the demise of the Tang, Yuan and Ming dynasties, researchers report in Friday's edition of the journal Science.

In addition, the team led by Pingzhong Zhang of Lanzhou University in China noted a change in the cycles around 1960 which they said may indicate that greenhouse gases released by human activities have become the dominant influence on the monsoon.

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The Wanxiang Cave is in Gansu Province, a region where 80 percent of the rainfall occurs between May and September.

Chemical concentrations in the stalagmite indicate a series of fluctuations lasting from one to several centuries and roughly similar to records of the Little Ice Age, Medieval warm period and Dark Age cold period recorded in Europe.