Very little light reaches the bottom of tiankeng, which means “heavenly pits” in Mandarin. Tiankeng are 330-foot-deep (100 meters) holes in China’s southwestern karst landscape. The plants that grow at the bottom are perforce shade-loving, and may include ancient species unknown to science. Unsurprisingly, they have lower levels of carbon than surface plants (plants get carbon from atmospheric carbon dioxide via photosynthesis), but higher levels of all other plant nutrients.