How life thrives at deep-sea vents without sunlight

HostI used to think that the bottom of the ocean was just a vast, empty basement. It's cold, the weight of the water is crushing, and there's absolutely no light. Without the sun to grow plants, you would assume the whole place is a graveyard where things just wait for scraps to fall from above. But it turns out there are these spots on the sea floor where life isn't just hanging on, it's actually booming. It feels like finding a forest in the middle of a vacuum. How's all that life even possible when the main power source for the planet can't reach them?

GuestIt really was one of the biggest shocks in science. Back in the late seventies, when people first sent cameras down to these cracks in the ocean floor, they expected to see bare rock. Instead, they found these tall chimneys spitting out black, cloudy water, and they were surrounded by heaps of living things. There were huge worms as long as a person, white crabs crawling over each other, and thick mats of what looked like white fuzz. It was like a city in the dark. The reason they can be there's that the earth itself is providing the energy. Deep under the sea floor, the rock is hot and full of minerals. Sea water seeps down into cracks, gets superheated, and then blasts back out. That water is a thick soup of chemicals, and that soup is what feeds everything else.

HostBut you still need something to turn that soup into actual food. On land, grass and trees do that using light. If you take the light away, how do you keep the whole thing from falling apart?

GuestLife found a different way to do the same job. There are these tiny germs, or bacteria, that have figured out how to eat those chemicals. They go after stuff like sulfur, which is basically the stuff in matches that smells like rotten eggs. These germs take the energy held inside those chemical bonds and use it to build their own bodies. It's the same basic idea as a plant using a sunbeam, but they use a chemical battery instead. These tiny things are the grass of the deep sea. They're the start of the whole food web. Some float in the water, some grow in thick carpets on the rocks, and everything else down there's either eating them or living with them. It turns the whole idea of how life works on its head because it means you don't need a star to have a living world. You just need a hot planet with the right stuff in the rocks.

HostWait, eating chemicals? That sounds like a stretch. How do the bigger animals get enough to eat? I mean, a giant worm can't just graze on tiny germs all day.

GuestWell, that's where it gets even weirder. Take those big tube worms. They're bright red and live in white tubes stuck to the rocks. These things don't have a mouth. They don't have a stomach or a way to poop. They're basically just a long bag of germs. They have this red, feathery bit at the top that pokes out into the water to grab the sulfur and oxygen. They pipe those chemicals down into their bodies, where billions of these germs are living. The germs use the chemicals to make sugar and other food, and then they share that food directly with the worm. The worm provides a safe home and a steady supply of raw materials, and the germs keep the worm fed. It's a perfect deal. Without those germs, the worm would starve in days.

HostIf the water is coming out of these chimneys, it must be boiling. If the worms are sitting right on top of them, why don't they just get cooked?

GuestThat's the big catch. The water coming out can be four hundred degrees, which is way hotter than boiling. It stays liquid only because the weight of the ocean above is pressing down so hard. If you touched that water, you would be gone in a second. But the ocean around it's nearly freezing. There's this tiny, thin line where the hot chemical water mixes with the cold sea water. That's where the life sits. It's a very tight space. If a worm grows a few inches too close to the heat, it cooks. If it's too far away, it freezes or runs out of food. It's like trying to stay warm by a bonfire during a blizzard, but the fire is made of acid and the air is cold enough to turn you to ice.

HostIt sounds so fragile. If the chimney stops spitting out that hot water, does the whole city just die off?

GuestIt does. These vents don't last forever. The plumbing under the sea floor shifts, the heat moves, and the vent goes cold. When that happens, the germs die, the worms die, and the crabs move on to find a new spot. It becomes a ghost town of empty white tubes. The big mystery we're still trying to solve is how they find the next one. These vents can be hundreds of miles apart. Somehow, the tiny babies of these worms and crabs have to drift through the cold, dark desert of the deep sea and find a new chimney before they run out of luck. They might follow the smell of chemicals or use the underwater currents like a highway. It's a race against time in the dark.

GuestWe still don't know how a tiny worm baby finds a new vent that's hundreds of miles away in the pitch black.

HostThose empty white tubes are a reminder that even in the deepest dark, life will find a way to plug in and turn the lights on.