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6-Nov-2008

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American Association for the Advancement of Science

Cave's clues: The ups and downs of Chinese history

In China and many other countries in Asia, a change in winds called the Asian Monsoon brings wet and dry seasons to the area. The wet time is especially important for bringing lots of rain to farmers growing rice and other food. Now, a new discovery in a Chinese cave shows that the Monsoon may have played a big part in Chinese history for nearly 2,000 years.



View from the inside of Wanxiang Cave. [Image courtesy of Science/AAAS]

In China and many other countries in Asia, a change in winds called the Asian Monsoon brings wet and dry seasons to the area. The wet time is especially important for bringing lots of rain to farmers growing rice and other food. Now, a new discovery in a Chinese cave shows that the Monsoon may have played a big part in Chinese history for nearly 2,000 years.



View from the inside of Wanxiang Cave. [Image courtesy of Science/AAAS]

The discovery was a stalagmite—a rock that looks like a big icicle poking up out of the cave floor. Stalagmites are built from water-dissolved minerals that drip, drip, drip onto the floor over hundreds of years. Cut a stalagmite open, and you'll see rings of growth just like in a tree stump, which scientists can examine to find out how wet or dry it was each year of the stalagmite's "life."

The stalagmite discovered by Pingzhong Zhang of China's Lanzhou University and fellow scientists is a 1,810 year record of the wet and dry times of the Asian Monsoon. And when the scientists matched up the stalagmite's record with what we know about Chinese history, they found some interesting things. When the Monsoon was bringing good rain, the leaders of China were strong and ruled over a kingdom with lots of rice and a growing population. But the dry years match the end of some of China's most famous ruling families, including the Tang, Yuan and Ming dynasties.

During these thousands of years, natural changes in the sun's energy and the glaciers in northern Europe affected the Monsoon's strength. Since 1960, however, the strongest influence on the Asian Monsoon has been human air pollution, the scientists found.

These findings appear in the 7 November issue of the journal Science.

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