When you think of creepy, ghostly, evil creatures thriving in the darkness of hell, you probably turn your imagination to the bottom of the oceans, like this terrifying big fin squid @trumpman wrote about.

But to me, these creatures are usually too colourful and sluggish to really make my skin crawl. What really creeps you out are the cave dwellers. Those who live on land and breathe air, yet they never see the light of day. I'm not talking cute little bats here, I mean, NEVER see the light of day. Some of these creatures have been cut off from sunlight and indeed the rest of the entire earth for so long that their bodies have mutated to adapt accordingly, and we end up with some incredibly unique, yet hauntingly familiar creatures. But what truly fascinates me is the story of how they got there, how they didn't die, and all the other mysteries that come with their existence.

So first let me explain the hows via a very special place, and in part 2 we'll look at some tame horrors, continuing on to your worst nightmares.

Welcome to the most isolated place on Earth.

Movile Cave

Caves are easily the least explored places on land, so there are a whole lot of mysteries involved in the life thriving in them. First and foremost: How on earth are they even alive?

In some cases, caves have been completely cut off from anything else for millions of years. in 1986, Movile Cave was discovered and it turned out to have not had any contact with the outside world for about 5.5 million years! Movile Cave in Romania has so many secrets it's unreal, though most caves of this type are typically full of life unique to that one space. But Movile Cave is extreme.

To explore it, you have to first abseil down 20 metres that was dug out by humans to get to the cave, then you have to struggle through little limestone and clay tunnels in extreme humidity and sweaty conditions, where you then arrive in a room with a toxic atmosphere of sulfur and a lake that stinks of sulfuric, rotten eggs. At this point the air is only 10% oxygen and will destroy your organs within a few hours of staying there (usual air is 20%) and the carbon dioxide content is a 100 times normal levels (remember this). Moving on, you have to dive into the rotten egg lake and traverse through a maze of underwater passages, slipping through tiny gaps in rocks until you finally arrive at a pocket of air. I'm not making this stuff up! This is not a computer game!

Even here. EVEN HERE, there is life, and lots of it.

But let's think about this for a minute. How do these creatures survive? They eat, right? What do they eat? Some eat other animals, but those animals eat plants. Plants need sunlight. If there is no sunlight for millions of years, where on earth are they getting their base food supply?

This was a legitimate mystery for Serban M. Sarbu et al who sought out to answer this question. Looking at other caves as a comparison, the animals down those places find food from the water that works its way down from the surface; algae, bacteria and whatnot. This is how you get stalagmites, from centuries of steady dripping from above.

But... there are no stalagmites at all in Movile cave. This implies no water comes from above. To put more nails in the coffin of that idea, the cave was beneath a thick layer of impermeable clay, and when doing a radioactive analysis looking for remnants of caesium and strontium left over from the Chernobyl disaster nearby, which can be found everywhere surrounding the cave, none was found, whatsoever.

Nothing had seeped into this cave, ever. So, any guesses how the creatures eat?

No?

Well, it turns out that water also comes from underground. But this water never had contact with the outside world or anything organic either. For a start this water is at least 25,000 years old itself. But the water does have a thick, frothy foam on the surface, described as rippable wet tissue paper. Here, they finally found the source: Millions of bacteria.

And not just any bacteria. These are autotrophic, chemosynthetic bacteria. Autotrophic essentially means any organism that gets its food from inorganic stuff; plants, algae and these bacteria are examples of that. But did you remember that the cave has 100 times more carbon dioxide in the atmosphere? *That's* their source of carbon. But they still need energy, and without sunlight, there has to be another way.

This is where chemosynthesis comes in. They actually rely on the chemical reactions through oxidation; between sulphide and other sulphur ions into sulphuric acid, and ammonium into nitrate. This is how the tiny bacteria get their energy, which in turn allows them to grow with the carbon found in the atmosphere, allowing trapped creatures to feed off them and thrive for 5.5 million years from way back when some idiot caused an avalanche or something.

This discovery had some unexpected benefits to the research. It actually explained why the air was so grossly carbon-ey, but also why the cave was so big - the sulphuric acid erodes the limestone, which in turn releases the CO2.

Oh, but there's more! A second type of bacteria, the methanotrophs get their energy from methane, which gets converted into methanol and formate which also feeds other bacteria.

You see? Life will find a way.

But honestly, the process itself isn't that special. Despite being so isolated and finding a niche way to survive, these bacteria have evolved little, and are still very simply just finding carbon supplies through basic bacterial means. However, scientists were quick to realize the potential benefits of harnessing these bacteria's abilities for extracting carbon from the air, something very useful for battling climate change. Being an organism that essentially lives in the futuristic dystopia that is the runaway greenhouse Earth, they're a prime candidate to help us find solutions.

As for the rest of the life in this cave, well... they did evolve, a lot. Caves on the whole are insane places for evolutionary creativity, but you'll have to wait until next time to find out more! (Or just Google or whatever)

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So there you have it, a real-world example demonstrating how well the cycle of life can exist just about anywhere. Next time we'll take a deep, ugly look into that life to really appreciate it. Thanks for reading!

_{Sorry, did I scare you? mwhahaha}

Image Sources:

Movile Cave Map
Romania Map
Chernobyl Disaster Radiation
Chemosynthetic Bacteria
Cave Scorpion