An ancient "lost" forest packed with more than 1,200 rare species has been found thriving at the bottom of a 600-metre sinkhole dubbed the "Heavenly Pit." The sinkhole, located in Xiaozhai Tiankeng in Fengjie County, China, is the deepest and largest natural sinkhole on Earth.
From the rim, it looks like a gash in the landscape, but far below sits a hidden, subtropical world with towering trees, dense undergrowth, and wildlife that has survived in isolation. Scientists say the crater was carved out over roughly 128,000 years as acidic rainwater slowly dissolved the region's limestone bedrock, creating a huge network of caves above the roaring Difeng underground river.
Formation and Size of the Sinkhole
Those caverns eventually collapsed in two separate stages, forming a dramatic double-nested sinkhole that drops between 511 and 662 metres. Despite its depth, the pit is so enormous - around 600 metres long and 500 metres wide - that enough sunlight filters down to support a thriving microclimate at the bottom.
That has allowed a primeval jungle to flourish inside the abyss, complete with ancient trees and thick vegetation more commonly associated with the surface, Earth.com reported. Biologists have reportedly recorded about 1,285 plant and animal species in and around the sinkhole, including "living fossils" such as ginkgo trees, rare mosses, the Chinese giant salamander and even elusive clouded leopards, according to reports.
Adaptation and Discovery History
Researchers have also found that the sinkhole's plants appear to be adapting in unusual ways to the low-light, high-moisture environment. Recent studies suggest leaves from the underground forest store significantly more nitrogen, phosphorus and calcium - but less carbon - than plants growing outside on the surface, a quirk experts say could be tied to surviving with limited light.
Locals in Fengjie County have known about the gaping chasm for generations. The sinkhole takes its name from Xiaozhai ("little village"), an old, abandoned mountainside settlement near the rim, where farmers and villagers have long spoken about the terrifying hole in the ground. But outside the area, the true scale of Xiaozhai Tiankeng was not properly recorded until 1994, when an international team of British and Chinese cavers mapped and explored it during the China Caves Project.
Tourism Threats and Recent Discoveries
The "lost world" obsession online, fuelled by renewed concern from science outlets this year about how fragile the hidden ecosystem could be, has reignited interest in the area. Reports have warned that mass tourism - and a huge 2,800-step staircase built to take visitors down into the chasm - could threaten species that may still be undiscovered, sending social media into overdrive.
Xiaozhai is the world-record sinkhole mapped in 1994, but in May 2022 explorers discovered a separate 192-metre-deep sinkhole in Guangxi with pristine woodland and ancient trees said to reach around 40 metres tall.
