What's Really at the Bottom of the Ocean?
The short answer
Snow. Marine snow is bits of plankton, desert dust, tiny shells and a lot of poop, glued together with slime. It falls day and night, all over the ocean. On the deepest floor on Earth, at the bottom of the Mariana Trench about 11 km down, thousands of years of it lie piled up.
Most of it never gets there. It sinks slowly, and on the way down it gets eaten or rots. Two kilometers down, only about 1% of the food made at the surface is still falling. The film follows one flake that makes the whole trip.
Why most snow never lands
A typical flake sinks about 100 m a day. At that speed the fall to the deepest floor takes months, and slow flakes can take years. There is a faster way down. A salp filters small things out of the water, and its poop can drop about a kilometer in a single day.
The water is crowded. Every night, billions of animals swim up toward the surface to eat, then go back down before sunrise. It is the biggest migration on Earth. Around a kilometer down, the water is full of animals that eat snow. The vampire squid doesn't drink blood. It catches falling snow on two sticky threads.
Most snow gets eaten or rots on the way down. Whatever gets eaten comes back out as poop and keeps falling, so a bit of food can be eaten and dropped more than once. Even so, at 2 km only about 1% of the food made at the surface is still falling.
Mountains, vents and the snow line
The first floor the flake reaches is a mountain. The mid ocean ridge runs along the sea floor for about 65,000 km. It is the longest mountain range on Earth.
Along it, black smokers shoot out water at about 350 °C. Lead melts at 327 °C. The water doesn't boil because the pressure of the deep sea keeps it liquid. The first time scientists measured one, it melted the tip of their thermometer. These chimneys can grow as tall as a 15 floor building, and scientists named one Godzilla.
Vents were first found in 1977, and the team hadn't brought a biologist. The giant tube worms that live there have no mouth and no stomach. Bacteria inside them make food from the chemicals in the hot water, with no sunlight at all. A vent's plume of hot water can rise a few hundred meters and carry snow back up with it.
Lower down, the peaks look snowy. That white is chalk: tiny plates and shells piled up. Deeper than about 4 to 5 km, the cold and the crushing pressure make the water dissolve chalk, so the white runs out. Glass shells last much longer. Diatoms build them, and diatoms make about a fifth of the oxygen our planet makes each year.
The abyss and the trench
The abyss is plains and hills of mud that cover more than half of the planet. Food is scarce out there. A thousand years of snow makes about 1 mm of mud. Sometimes the snow is a whale. One whale drops as much food on its spot as about 2,000 years of snow, and it feeds the floor for decades. Even the bones get eaten, by worms with no mouth and no gut.
The deepest floor is at the bottom of trenches. Trenches work like funnels: earthquakes shake mud loose and send it sliding downhill, so snow from all around ends up at the very bottom. No fish has ever been seen below about 8,400 m. At about 11 km, the pressure is over a thousand times what it is at the surface. That doesn't crush a flake. Pressure crushes air, like the air in lungs, bubbles and foam cups. A flake is just water and crumbs, with nothing in it to crush.
The bottom isn't the end. This floor slowly slides down into the Earth, and millions of years later some of what it carries comes back up in the lava of volcanoes. We have seen very little of the deep sea floor. All of it that people have ever looked at adds up to less than 0.001%, a patch about the size of Rhode Island.
Key numbers
| What | Number | Source |
|---|---|---|
| Depth of the deepest floor, at the bottom of the Mariana Trench | about 11 km | Greenaway et al. 2021 |
| Typical sinking speed of marine snow | about 100 m a day | Turner 2015 |
| Sinking speed of salp poop | up to about 1 km a day | WHOI Oceanus, salps |
| Share of the food made at the surface still falling at 2 km | about 1% | Lampitt and Antia 1997 |
| Length of the mid ocean ridge, the longest mountain range on Earth | about 65,000 km | NOAA Ocean Exploration, mid ocean ridge |
| Temperature of water from a black smoker | about 350 °C | WHOI Ocean Learning Hub, hydrothermal vents |
| Depth below which the water dissolves chalk | about 4 to 5 km | Harris et al. 2023 |
| Share of Earth's surface covered by the abyss | more than half | Smith et al. 2008 |
| Mud made by 1,000 years of snow on the abyss | about 1 mm | UBC EOSC 112, sediments part 3 |
| Food one whale drops on its spot of floor | about as much as 2,000 years of snow | Science News, whale falls |
| Depth below which no fish has ever been seen | about 8,400 m | Yale E360, deepest fish |
| Share of the deep sea floor people have ever seen | less than 0.001%, about the size of Rhode Island | Bell et al. 2025 |
What the film simplifies
- The film follows one flake all the way to the bottom. Real flakes break apart, get eaten and come back out as poop many times. Very few reach the deepest floor as anything like the same flake.
- Pressure, the flake, the blobfish and the snailfish talk. Pressure is really just the weight of all the water above, drawn as a character.
- The blobfish's famous saggy face happens when it is hauled up from deep water. In the film it springs back to plump the moment it is home. That quick change is drawn for the joke.
- Pressure says it is over a thousand times heavier at the bottom. More precisely, the pressure there is over a thousand times the pressure at the surface.
- A fall that takes months or years is squeezed into a film of about eight and a half minutes, and the flake's chalk hat fizzes away in seconds instead of slowly.
At a glance
Runtime 8 minutes 30 seconds · Topics: Marine snow, Deep sea floor, Hydrothermal vents, Ocean trenches · Captions on YouTube · Full script below
Test yourself
Marine snow sinks about 100 m a day. If nothing ate it, roughly how long would a flake take to fall 11 km to the deepest floor?
Answer
About 110 days, nearly four months. Slower flakes can take years.
Black smoker water comes out at about 350 °C, hotter than the 327 °C that melts lead. Why doesn't it boil?
Answer
The pressure of the deep sea keeps it liquid.
At the bottom of the Mariana Trench the pressure is over a thousand times the pressure at the surface. Why doesn't it crush a flake of marine snow?
Answer
Pressure crushes spaces full of air, like lungs, bubbles and foam cups. A flake is just water and crumbs, so there is nothing in it to crush.
The script
Read the script
Blobfish: Don't look at me! I'm not decent!
Host: Meet the blobfish. In 2013, an online vote named it the ugliest animal on Earth.
Blobfish: That vote was RIGGED!
Host: He's not wrong. That face is what happens when you haul a soft fish up from a kilometer down.
Blobfish: Take me home!
Blobfish: Ahh. Much better.
The Flake: Oops! Sorry! Which way is the bottom?
Blobfish: Down, darling. Everything goes down.
Pressure: The bottom? Ha! Snow never makes it to the bottom in one piece.
The Flake: I will.
Host: That's Pressure, the weight of all the water above. Down here, it's the boss.
Host: And that's a flake of marine snow. It wants to fall eleven kilometers, all the way to the deepest floor on Earth.
Host: So what's really at the bottom of the ocean? Let's fall with it and see.
Blobfish: Darling, what ARE you?
The Flake: A bit of everything! Some plankton. A speck of desert dust. A tiny glass shell.
The Flake: And a chalk plate. I wear it as a hat.
The Flake: And the rest is mostly... poop.
Blobfish: ...I need to sit down.
Host: Snow like this is glued together with slime, and it falls day and night, all over the ocean.
Blobfish: Well. This is my stop. Try not to get eaten, darling.
The Flake: ...Eaten?
The Flake: Whoa! Where's everybody going?
Host: Up! Every night, billions of animals swim up toward the surface to eat, and back down before sunrise.
Host: It's the biggest migration on Earth. And it happens every single night.
The Flake: Excuse me! Sorry! Wrong way! Down, please!
The Flake: Everybody's faster than me!
Host: Snow is slow. Most flakes sink about a hundred meters a day.
The Flake: So I'll reach the bottom by...
The Flake: ...spring?
Host: If you're lucky. Slow flakes can take years.
The Flake: YEARS?!
Host: Unless you take the express lane.
Host: That's a salp. It filters the water for anything small, and its poop can drop a kilometer in a single day.
Host: One of the fastest rides to the bottom of the ocean? Getting pooped.
Host: But around a kilometer down, the water is full of things that eat snow.
Host: Like the vampire squid.
The Flake: A VAMPIRE?
Host: Relax. It doesn't drink blood.
The Flake: Phew.
Host: It eats snow. With two sticky threads.
The Flake: WHAT?!
The Flake: It got Gary!
The Flake: Ooh, a light! Is that the bottom?
Pressure: Kid. Never swim toward the light down here.
Pressure: Snow never makes it.
Host: Pressure has a point. Most snow gets eaten, or rots on the way down.
Host: Two kilometers down, only about one percent of the food made up top is still falling.
The Flake: Still in one piece!
The Flake: ...GARY?!
Host: Whatever gets eaten comes back out as poop, and keeps on falling.
The Flake: See you at the bottom, Gary!
The Flake: The bottom! I MADE IT!
Pressure: That's a mountain, kid.
Pressure: The longest mountain range on Earth is down here with me. 65,000 kilometers of it.
The Flake: ...Oh.
The Flake: Whoa! Is that smoke?
Host: It's water, shooting out of the floor at 350 degrees Celsius. Hot enough to melt lead.
Host: The first time scientists measured one, it melted the tip of their thermometer.
The Flake: Then why isn't it boiling?
Pressure: Boil? With me sitting on it?
Host: Chimneys like this can grow as tall as a fifteen floor building. Scientists named one Godzilla.
The Flake: ...I'm staying away from Godzilla.
The Flake: And there's a whole town down here!
The Flake: Excuse me, where's your mouth?
Host: It doesn't have one. Or a stomach. Bacteria inside it make its food, from the chemicals in that hot water.
The Flake: Food with no sunlight?
Host: When scientists found the first vents in 1977, they hadn't even brought a biologist.
The Flake: Ooh, I want a closer look!
The Flake: No no no no NO!
Host: Hot water rises, and it carries snow with it. A vent's plume can climb a few hundred meters.
Pressure: Told you, kid.
The Flake: Still... in one piece.
Host: Lower down, the mountaintops look snowy.
The Flake: Snow! Like me!
Host: That's chalk. Tiny plates and shells like your hat, piled up on the peaks.
Host: But deeper than about four or five kilometers, the white runs out.
The Flake: My hat! MY HAT!
Pressure: Sorry, kid. That one's me.
Host: Down here, the cold and the crushing pressure make the water dissolve chalk.
The Flake: It was a really good hat.
Host: Your glass shell, though? That lasts much longer.
The Flake: Glass? I'm wearing GLASS?
Host: A tiny living thing called a diatom built it. Diatoms make about a fifth of the oxygen our planet makes each year.
The Flake: ...So I'm kind of a big deal.
The Flake: Still... mostly... in one piece.
The Flake: Okay. THIS is the bottom.
Pressure: It's A bottom.
Host: The abyss. Plains and hills of mud that cover more than half of our whole planet.
Host: The very deepest floor is over there, at the bottom of a trench. And snow can't swim.
The Flake: So I'm stuck?
Host: Out here, a thousand years of snow makes about one millimeter of mud.
The Flake: I'll be buried in a millimeter of mud, and nobody will even notice!
Host: Sometimes, the snow is a whale.
The Flake: ...Okay. They'll notice that.
Host: One whale drops as much food on its spot as about two thousand years of snow.
Host: It feeds the floor for decades. Even the bones get eaten, by worms with no mouth and no gut.
The Flake: What is it with you guys and mouths?
The Flake: Why do you keep saying snow never makes it?
Pressure: Because I've watched it fall every day for millions of years.
Pressure: Most of it never makes it.
The Flake: Some does.
Pressure: ...Some does.
The Flake: What was that?
Pressure: Earthquake. Hold on, kid.
The Flake: ...No. I'm letting go.
The Flake: WHEEEEE!
Host: Trenches work like funnels. Snow from all around ends up at the very bottom.
Host: The Mariana Trench. The deepest place on Earth.
Snailfish: Oh, hi! Where are you going?
The Flake: The bottom!
Snailfish: Lucky. Everybody gets to go past me. Submarines. Robots. Even a plastic bag!
Snailfish: What's it like up top?
The Flake: Bright! And there's a big yellow guy up there who sulks a lot.
Snailfish: Will you tell me what's down there?
The Flake: I'll tell you everything. Promise.
Host: Below about 8,400 meters, no fish has ever been seen.
Host: Add up all the deep sea floor people have ever laid eyes on. It's less than a thousandth of one percent.
Host: A patch about the size of Rhode Island.
The Flake: So I'll see something nobody's ever seen?
Pressure: If you make it, kid.
Pressure: Last stop. Down here, I'm over a thousand times heavier than at the surface.
Pressure: Let's see that one piece.
The Flake: Okay. Give me everything you've got.
The Flake: ...Is it happening?
Pressure: I'm DOING it!
Host: Pressure crushes air: lungs, bubbles, foam cups. A flake is just water and crumbs. There's nothing in it to crush.
Pressure: ...Huh.
Pressure: Go on, then.
Host: And nobody saw it land.
The Flake: I made it. I MADE IT!
The Flake: Not yet! Please! I just got here!
The Flake: ...Thank you.
The Flake: Hi... everybody?
Host: Thousands of years of snow, piled up at the bottom of the world.
The Flake: SNAILFISH! IT'S SNOW! IT'S ALL SNOW!
Snailfish: ...So the bottom falls right past me. Every day!
The Flake: So now I stay down here forever?
Pressure: Nothing stays down here forever, kid.
Host: This floor slowly slides down into the Earth.
Host: And millions of years later, some of what it carries comes back up, in the lava of volcanoes.
The Flake: So I'll see the top again?
Pressure: Bring a hat.
Host: So what's really at the bottom of the ocean?
Host: Pieces of the top. Still falling.
Blobfish: FINALLY. My good side.
Sources
- In 2013 a vote named the blobfish the ugliest animal on Earth; its saggy face comes from being hauled up from deep water.Science News, Gory Details blog, 2013
- Marine snow: what it is made of and how it falls.NOAA Ocean Service, marine snow
- Sinking speeds of marine snow and poop.Turner 2015
- Every night billions of animals swim up to eat, the biggest migration on Earth.Scientific American, nightly migration
- Salps filter the water, and their poop sinks up to about a kilometer a day.WHOI Oceanus, salps
- The vampire squid eats marine snow, caught on two sticky threads.MBARI, vampire squid
- At 2 km, about 1% of the food made at the surface is still falling.Lampitt and Antia 1997
- The mid ocean ridge is about 65,000 km long, the longest mountain range on Earth.NOAA Ocean Exploration, mid ocean ridge
- Black smoker water comes out at about 350 °C and is kept liquid by pressure; vents were found in 1977.WHOI Ocean Learning Hub, hydrothermal vents
- Lead melts at 327 °C.Wikipedia, Lead
- The first vent temperature measurement melted the probe's tip.WHOI, vent history: the melted probe
- The 1977 vent discovery team had no biologist aboard.WHOI, vent history: 1977
- A 15 story vent chimney named Godzilla.WHOI, Godzilla, Sasquatch and Homer Simpson
- Giant tube worms have no mouth or stomach and are fed by bacteria inside them.MBARI, giant tubeworm
- A vent's plume can rise a few hundred meters.WHOI Dive and Discover, vent plumes
- Chalk on the sea floor runs out deeper than about 4 to 5 km.Harris et al. 2023
- Why cold, deep water under high pressure dissolves chalk.Wikipedia, carbonate compensation depth
- Glass shells last longer on the deep floor than chalk.UBC EOSC 112, sediments part 2
- Diatoms make about a fifth of the oxygen produced on Earth each year.Armbrust 2009
- The abyssal sea floor covers more than half of Earth.Smith et al. 2008
- On the abyss, a thousand years of snow makes about 1 mm of mud.UBC EOSC 112, sediments part 3
- One whale fall delivers as much food as about 2,000 years of falling snow, and whale falls last for decades.Science News, whale falls
- Bone eating worms with no mouth and no gut.MBARI, bone eating worms, 2017
- Marine snow has fallen for millions of years.Logan et al. 1995
- Earthquakes send mudslides down into trenches.Kioka et al. 2019
- Trenches collect food from all around, and the trench floor is full of life.Glud et al. 2013
- Depth of the Challenger Deep, about 11 km.Greenaway et al. 2021
- The deepest fish ever filmed, the record behind the film's line that no fish has been seen below about 8,400 m.Yale E360, deepest fish
- Robots have reached the deepest part of the ocean.WHOI, Nereus reaches the deepest ocean
- A plastic bag has been found at the bottom of the Mariana Trench.Mongabay, 2018
- People have seen less than 0.001% of the deep sea floor, about the area of Rhode Island.Bell et al. 2025
- Pressure rises by one atmosphere for every 10 m of depth.NOAA Ocean Service, pressure
- Sea cucumbers live at the bottom of the deepest trench.ScienceDaily, 2013
- Sea floor slowly slides down into the Earth at trenches.USGS, understanding plate motions
- Trench mud comes back up in the lavas of Mariana volcanoes.White Rose eprints, trench mud in Mariana lavas