Fragile world: Enormous sinkholes in China brim with ancient life, yet they risk vanishing forever (photos).

For thousands of years, "heavenly pits," or "tianken" in Chinese, remained unexplored, even though two-thirds of the more than 300 karst sinkholes worldwide are located in China. Most of these sinkholes are scattered across the western part of the country, with the Guangxi province in the south having more than anywhere else—science recognizes about three dozen sinkholes, according to BBC.

For a long time, these areas were left untouched by humans, as people feared demons and ghosts lurking in the mist that rose from the depths of the forest. Eventually, drones and a few brave explorers ventured into these places, untouched since the time of the dinosaurs that roamed the Earth millions of years ago. Consequently, the sinkholes in China have gradually turned into a tourist attraction and have become incredibly vulnerable.

The largest and most recent discovery was made in Guangxi two years ago: scientists found an ancient forest with trees reaching heights of 40 meters. Researchers now believe that these massive sinkholes literally "stop time," preserving unique ecosystems for centuries. At the same time, the latest discovery has started attracting tourists and developers, raising concerns among scientists that these rare finds may be lost forever.

According to Fei Ge, one of the first researchers of karst sinkholes, he now works as a guide, helping people uncover the secrets of these ancient pits. The researcher notes that each of these karst sinkholes essentially has its own microclimate: winds rush through the tunnels, and evaporating water from rivers inside the caves creates mist.

Scientists have studied the sinkholes and discovered new plants and other findings within them. When the results of their work were published in journals, rumors about the discoveries spread, and more researchers began visiting the site to explore the karst sinkholes. According to Fei, in the past decade, researchers from the UK, France, and Germany have visited this area.

In fact, karst sinkholes are relatively rare worldwide; however, in China, and especially in Guangxi, they are abundant due to the plentiful limestone. As an underground river slowly dissolves the surrounding limestone rock, it creates a cave that expands upward toward the surface.

Eventually, the ground collapses, forming a sinkhole with a depth and width of at least 100 meters to be classified as a pit. Some karst sinkholes, like the one discovered in Guangxi, are much larger: its depth is about 300 meters, and its width is around 150 meters.

For scientists, these cave pits represent a journey through time to a place where they can study animals and plants they believed to be extinct. They have also discovered species they had never seen or known before, including wild orchid varieties, ghostly white cave fish, and various spiders and snails. Protected by sheer cliffs, jagged mountains, and limestone caves, these plants and animals have thrived deep underground.

However, scientists now fear that tourism revenue may outweigh the demands for scientific research. About 50 kilometers from the nearest settlement, Ping'e, developers have constructed the "highest observation deck," which offers views of the second-deepest karst sinkhole in the world—Dashivei. Tourists can peer into this "heavenly pit" to a depth of 500 meters.

According to Dr. Lina Shen, the leading researcher on karst sinkholes in China, people should better protect the sinkholes, as they are home to many rare and endangered plant species. By studying the karst sinkholes, scientists also hope to learn how the Earth has changed over tens of thousands of years and gain better insights into the impact of climate change. At least one karst sinkhole in Guangxi has already been closed to tourists to protect unique orchid varieties.