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Place 04 · The Ridge and the Trench · Chapter 6 of 7
Life Without the Sun
In 1977 a submarine full of geologists went looking for hot springs on the seafloor near the Galápagos and found giant clams, red-tipped worms and a whole ecosystem that never needed the Sun.
About 15 minutes · 1 video · 1 3D model · 2 quick activities
Start here
No biologists on board
On February 17, 1977, the submersible Alvin dived 2,500 m to the Galápagos Rift, a spreading ridge near the islands from Place 03. The scientists aboard were geologists and chemists hunting for hot springs, and there was no biologist on the team. Instead of bare rock they found warm, shimmering water crowded with white clams up to 30 cm long, mussels, crabs, purple octopuses and tubeworms with red tips.
Watch this
See it move
Woods Hole Oceanographic Institution — What are hydrothermal vents? Two and a half minutes from the institution that runs Alvin, which seems like the right people to ask.
While you watch, look for
- Where the hot water at a vent comes from
- What the microbes at a vent use for energy instead of sunlight
- Something you did not expect. Hold onto it.
The short version
Three things going on here
The plumbing
Hot springs on the ridge
At the ridges, cold seawater seeps down through cracks in the young crust, gets superheated by magma below and gushes back out loaded with dissolved minerals. When it meets the near-freezing water around it, metal sulfides drop out as tiny black particles, so the hottest vents, black smokers, pour out what looks like smoke at up to about 350 °C. The minerals pile up into chimneys 20 m tall or more.
The trick
Food from chemicals
Vent water is rich in hydrogen sulfide, the gas that smells like rotten eggs. Microbes use the energy in it to turn carbon dioxide and water into food: chemosynthesis, the chemical cousin of photosynthesis. Those microbes are the base of the whole vent food web, a second base for life on Earth that runs on chemical energy instead of sunlight.
The worm
No mouth, no gut, no problem
Giant tubeworms, Riftia, grow more than 2 m long, and the adults have no mouth and no gut. Their red plumes soak up hydrogen sulfide and oxygen from the water and deliver them to bacteria living inside an organ called the trophosome, and the bacteria make the worm’s food. Two species living together so that both benefit is called symbiosis.
Photos: Eva Bronzini, FAN DENG, Diego Sandoval / Pexels
Play with it
Fly around a real vent chimney
This 3D model is Sequoia Vent, a mineral chimney more than 30 m tall, nearly as high as a ten-story building, explored by the Nautilus team’s ROV Hercules in 2025 at a vent field in the Northern Mariana Islands, the same corner of the Pacific as the trench from Chapter 3. Drag to spin it and scroll to zoom: every bit of it was built from minerals that dropped out of hot vent water.
3D model: “Sequoia Vent” by EVNautilus (Ocean Exploration Trust) on Sketchfab (CC BY).
Two questions to answer while you are in there
- The Nautilus team found the chimney covered in shrimp, snails, crabs and limpets. Zoom in: where on the chimney would you expect the animals to crowd, and why?
- This chimney grew out of minerals dropping out of hot water. What would happen to the animals living on it if the vent below it shut off?
Try it yourself
Check yourself
Try it
The Cast of the Vents
Flip each card to meet a vent animal or microbe and the trick that keeps it alive in the dark.
Try it · interactive
Vent Food Web
Build a food web at a hydrothermal vent, starting from hot vent water and chemosynthetic microbes and adding tubeworms, mussels, snails, crabs and fish; then switch the vent off to see what collapses, and compare it with a food web that runs on sunlight.
Open the Vent Food Web in its own window (opens in a new tab).
Words you will hear
Four terms, that is all
Hydrothermal vent
Seafloor hot spring, usually on a spreading ridge
Chemosynthesis
Making food from chemical energy, not sunlight
Black smoker
Vent chimney pouring out hot, black, mineral-rich water
Symbiosis
Two species living closely together, often both benefiting
Check your understanding
Practice the whole chapter
Everything in this chapter, in eight quick questions. Retry as often as you like. Read the feedback on every answer, right or wrong, because that is where the learning is.
Practice
Practice: Life Without the Sun
Eight questions covering the video, the three cards, the four terms and the interactive above.
If you want more
Go deeper
- Webb 4.11 — Hydrothermal Vents — LibreTexts · 6 minutes
- Oceanography 101 (MiraCosta) 15.17 — Hydrothermal Vents — LibreTexts · 3 minutes
- Woods Hole Oceanographic Institution — The Discovery of Hydrothermal Vents: 1977 — WHOI · 6 minutes
Photo credits (Pexels): Attila Pergel, Greece-China News, Eva Bronzini, FAN DENG, Diego Sandoval.