Cave rocks reveal past climate changes.

Stalagmites have been sampled from caves in China and other caves from all over the world. Split into half, stalagmites reveal banding like an agate. The layers of calcite indicate periods of wet and dry weather and changing contents of trace elements. The bands are annual growth rings like in a tree and reveal ages of up to 100'000 years. The University of Minnesota researcher Hai Cheng measures uranium and thorium contents and reconstructs a weather and climate history. Photo shown here were taken by Hai Cheng who grew up in China, but now is a research scientist in the Department of Geology and Geophysics at the University of Minnesota.
Ref.: Ancient cave rocks reveal impact of climate change by Stephanie Hemphill

Cave gives clues to China's history.
In an article published in Science, the researchers say the stalagmite, found in Wanxiang Cave, China, told of strong and weak monsoon periods, which coincided with the rise and fall of several Chinese dynasties.
"....weak and consequently dry monsoon periods coincided with the demise of the Tang (618-907), Yuan (1271-1368) and Ming (1368-1644) dynasties."
"We have demonstrated that the cave records correlate well with many records, including the little ice age in Europe; the temperature changes in China and Northern Hemisphere and major solar variability."
Ref.: ABC Science : Cave gives clues to China's history.