An old forest has been found at the bottom of a giant sinkhole in China, with trees up to 40 metres 130 ft tall.
Scientists believe it could contain undiscovered plant and animal species.
Cave explorers in the Guangxi region of southern China alerted scientists when they found the sinkhole, which had a primitive forest inside. Among 30 sinkholes in Leye County, this is the largest, at 306 metres long, 150 metres wide and 192 metres deep.
Xinhua, a senior engineer at the Institute of Karst Geology of the China Geological Survey, told the state news agency that the site had three caves in its walls and a well-preserved primitive forest at the bottom.
Scientists trekked for hours to reach the base of the sinkhole to see what it contained. Chen Lixin, who led the expedition team, said that there was dense undergrowth on the floor that came up to his shoulders, as well as the trees.
I wouldn't be surprised to know that there are species found in caves that have never been described by science until now, he said.
The sinkhole-filled landscape is known as a karst landscape, formed primarily by the dissolution of bedrock by groundwater.
This means dramatic sinkholes and caves are created throughout the area. This one is rare, as it is deep but shaped so that enough light filters in, which means large trees can grow.