Imagine a labyrinth of caves cut off from the outside world for 5 million years, crawling with spiders, scorpions, worms and bizarre creatures never before seen by humans.
It sounds like the stuff of an Indiana Jones movie or the underground world of Jules Verne’s A Journey to the Centre of the Earth (1864), but the Movile Cave in southern Romania is no fantasy.
Discovered in 1986, it is one of the most isolated places on Earth and has proved a fruitful area of study for scientists, who believe it could offer clues about how life itself began.
The cave has remained sealed by the authorities since its discovery, and fewer than 30 people have set foot inside the unique ecosystem. Microbiologist Rich Boden, a lecturer in environmental microbiology and biotechnology at Plymouth University, is one of them. He was the first UK scientist to enter the cave system to explore how life has flourished there without sunlight for millennia.
“I was at school when the cave was first discovered,” recalls Boden. “I remember the TV report saying how they had found life in the cave, even though it had been completely sealed off for millions of years.
“But I forgot about it for about 20 years until I was doing my PhD at the University of Warwick and we were sent some samples from the cave for analysis.”
Working with microbiologists at Warwick, Boden published a paper on metabolism using the samples before leading expeditions into Movile to undertake fieldwork.
“It is out in the wilds of Romania, basically in the middle of very barren wasteland,” he says. “The location is actually why it was discovered. They were digging to see if it was a suitable place to build a power station and one of the holes broke through into the cave.”
Those wishing to enter must be lowered by rope 30m down narrow hand-cut shafts.
“You then spend about 10 minutes climbing through very narrow limestone clay tunnels - it’s very hot, too, about 25 ºC,” Boden says. “It’s a very dangerous environment, even for experienced cavers. I once fell about 2m, which really shook me up.”
Movile is also full of strange life slithering in the blackness. In short, it’s not for the fainthearted.
Boden explains: “You realise…that you are completely sealed off inside the cave - you feel totally alone. It’s completely dark and you have only your head torch to work with. The creatures down there have never seen light, so you can’t start blasting them with big spotlights.
“On my first visit I was actually due to go down with two other scientists, but it turned out one was arachnophobic and the other was claustrophobic. So I ended up being the only one to go down with the Romanian cavers, one of whom is a scientist and an associate on the project from Germany.”
If pitch darkness and precipitous rocks weren’t challenging enough, the other threat to human visitors is the cave’s toxic atmosphere.
“When you reach the lower levels, you are working with only 10 per cent oxygen, which means you cannot work for more than five or six hours otherwise your kidneys will pack in,” Boden says. “And because it feels very, very hot, even the most basic task can take a long time.”
Primarily, however, Boden was excited by the extraordinary scientific opportunity that exploration of the cave offered.
“You also realise you are getting access to somewhere very special - somewhere people have never seen,” he says. “With only 30 or so who have ever been inside the cave, it’s comparable to thinking about the numbers who have been to the Moon or into space.”
But unlike the barren moonscape or the vacuum of space, the Movile Cave is home to a thriving ecosystem. Despite being such a hostile environment for humans, its atmosphere successfully sustains waterborne mats of bacteria, which, in turn, support other forms of life in the darkness.
Tiny amphipods and nematodes feed on the chemotrophic bacteria, and these creatures in turn support scorpions, spiders and centipedes as long as 20cm.
So how does this complex food chain survive given that the cave is untouched by sunlight, the source of almost all life on Earth?
Rather than rely on photosynthesis to fix carbon dioxide into cells, the bacteria at the base of the Movile food chain convert substances such as ammonia and sulfides found in the cave’s geothermal waters into organic compounds - a process known as chemosynthesis.
The ecosystem is “probably what early Earth was like as the Sun could not pierce the atmosphere”, Boden argues.
“Nasa was once quite interested in the cave because the waters that were meant to be on Mars might have worked in the same way in supporting life.”
He adds: “Millions and millions of bacteria stick together and rest on water inside the cave like tissue paper, supporting some quite big organisms.”
Mysterious creatures unseen by humans have long been a source of fascination for naturalists, scientists, writers and film-makers alike.
From Shakespeare’s The Tempest through to the dinosaurs and human-sized fanged worms on King Kong’s Skull Island, the idea of the lost world has proved irresistible to the human imagination.
And Boden’s descent into Movile, with its previously unseen creatures, might easily be compared to science fiction tales, such as the bizarre ecosystem of Avatar’s Pandora or the wondrous world of Edgar Rice Burroughs’ The Land That Time Forgot.
“All the creatures we saw are completely white,” Boden observes. “None of them has any pigmentation in their body as there is no sunlight - you can see right through them.”
The organisms display other peculiar characteristics, too, thanks to the power of Darwinian selection.
“They are completely adapted to their surroundings, which means they have no eyes as they would never need to use them. However, they have bigger antennae and bigger legs than similar species.
“I thought it was odd that the spiders still spin webs down there because there are no flies, but then you see there are these little insects called spring-tails, which bounce into the air, and are caught by the webs. It really is the stuff of science fiction.”
The Movile Cave has in fact inspired several feature films, including The Descent (2005), a UK horror movie directed by Neil Marshall.
“Instead of having white eyeless insects, there were some white eyeless people, which attack female cavers,” Boden says of the film, adding: “I thought it was pretty awful.”