In the south-east of Romania, in Constanța county close to the Black Sea and the Bulgarian border, there lies a barren featureless plain. The desolate field is completely unremarkable, except for one thing.
Below it lies a cave that has remained isolated for 5.5 million years. While our ape-like ancestors were coming down from the trees and evolving into modern humans, the inhabitants of this cave were cut off from the rest of the planet.
Despite a complete absence of light and a poisonous atmosphere, the cave is crawling with life. There are unique spiders, scorpions, woodlice and centipedes, many never before seen by humans, and all of them owe their lives to a strange floating mat of bacteria.
To enter, you must first lower yourself by rope 20m down a narrow shaft dug into the ground. The only light is from your helmet, which bounces around the walls as you descend.
You must then climb down through narrow limestone tunnels coated in an ochre clay, in pitch darkness and temperatures of 25 °C. These paths eventually open out into a central cavern containing a lake.
In the lake room, the atmosphere is heavy with harmful gases, principally carbon dioxide as well as the hydrogen sulphide from the water.
Strangely, the worse the air gets the more animals there are. It’s not at all obvious why that should be, or how the animals survive at all.
“These bacteria get their carbon from carbon dioxide just like plants do, the carbon dioxide level in the cave is about 100 times higher than normal air. But unlike plants, they obviously can’t use photosynthesis as there is no light.”
Rather than using light as an energy source, the Movile bacteria use a process known as chemosynthesis.
Another major group of bacteria get their energy and carbon from the methane gas that bubbles up through the waters of the cave. They are called methanotrophs.
In 1996, researchers categorised the animals in the cave. They included 3 species of spider, a centipede, 4 species of isopod (the group that includes woodlice), a leech never seen anywhere else in the world, and an unusual-looking insect called a waterscorpion.
The Movile Cave microbes could offer hints about how the first life formed on Earth. They are genetically similar to those found in geothermal vents, which are also rich in carbon dioxide, sulphides and ammonia.
The conditions in both places may well be similar to the primordial Earth. In our world’s early years, the Sun’s light was obscured by an atmosphere thick with carbon dioxide, methane and ammonia. It could be that the first living cells were similar to those found in Movile Cave.
Almost 30 years after its discovery, Movile Cave remains perhaps the most isolated ecosystem on the planet. It surely has many more secrets to give up. There are plenty more organisms buried in the cave’s sediments, waiting to be identified, and they could help us understand some of our deepest questions about the nature of life.