How Deep Is the Ocean?

Archimedes (telling the story): This is a story about the sea. It is wet, it is dark, and it is much deeper than you think. If you are scared of the dark, you may hold a grown-up's hand. Leo held my wing. I allowed it.

Leo: Mei, look! A little crab! Hello, little crab!

Mei: Never mind crabs, Leo. I bet I can swim all the way to the bottom of the sea! Race you!

Leo: You can't, Mei! Nobody can. Does the sea even have a bottom? How deep does it go?

Professor: How deep is the ocean? Ooh, what a splendid question! And I know just how we'll find out.

Archimedes (telling the story): Down at the harbour, the professor had built a submarine. It was round, it was brass, and it looked exactly like a kettle. Nobody had asked him to.

Archimedes: I am a clockwork owl. I do not enjoy baths. If I rust, I am blaming the kettle.

Leo: Is it very dark down there? I'm... a little bit scared of the dark.

Professor: It is, Leo! But don't you worry. The Kettle has the brightest lamps in the whole sea!

Archimedes (telling the story): Mei drew a face on a foam cup and called it Captain Cup. The professor tied it to the outside of the Kettle. He would not say why. He just smiled.

Archimedes (telling the story): The professor took the Kettle across the Pacific, the biggest, deepest ocean on Earth, to a spot near an island called Guam. Do not ask how. It was mostly string.

Professor: Right below us is the deepest place in the whole world. The Challenger Deep! It's nearly eleven kilometres down.

Mei: Eleven kilometres? That's further than our whole school cross-country! What does that even look like?

Professor (telling the story): Imagine the tallest mountain in the world, Mount Everest. Now pick it up and drop it into the deepest part of the sea. Splash! Its top would still be over two kilometres under the water!

Professor: Mei, you're in charge of the depth gauge. And when we reach the very bottom, the Kettle will whistle!

Archimedes: Why does it whistle?

Professor: It's a kettle, Archimedes! Hold on to your feathers. Down we go!

Professor (telling the story): This is the sunlight zone. Sunlight reaches down here, so it's bright and busy, full of fish, turtles and dolphins!

Leo: Professor, why is everything going blue? Even your orange hair's gone blue!

Professor: Remember the colours hiding in sunlight? The sea soaks them up as we go down. And red goes first!

Professor (telling the story): Red fades first, by the time you're as deep as a house is tall. Then orange, yellow and green. Blue reaches deepest of all. So down here, the world looks blue!

Archimedes: Absorption. A long word for the sea gobbling up the colours. It always takes the red ones first. Like the professor with sweets.

Professor (telling the story): Down we went, into the twilight zone. Here the light is dim and blue, like the sky just after sunset.

Leo: Professor! Those fish have little lights all along their tummies!

Professor (telling the story): Lanternfish! Every night, billions of them swim up towards the surface to feed, then sink back down by day. It's the biggest migration on Earth, and it happens every single day!

Mei: Every single night? That's like me running up a mountain before breakfast!

Archimedes (telling the story): Then something enormous swam by. A sperm whale, diving deep to hunt. It can hold its breath for more than an hour.

Professor: It's going hunting, Mei. Sperm whales love to eat squid. Very... big... squid.

Leo: Professor, look! It's a vampire! A vampire squid! Quick, hide!

Archimedes (telling the story): The vampire squid is not a vampire. It does not drink blood. It eats snow. I will explain the snow later.

Archimedes (telling the story): Below a thousand metres, there is no sunlight at all. None. It is darker than the darkest night, all day long, for ever.

Leo: Professor... I don't like it down here. It's very, very dark.

Professor: Then let me show you a secret, Leo. We'll keep one little lamp on. Archimedes, big lamps off!

Archimedes: Are you sure?

Archimedes (telling the story): For a moment, it was very dark outside. Then, one by one, lights came on. Not the Kettle's lights. Theirs.

Leo: It's not so dark after all! I can open my eyes now! They've got lights!

Professor: Scientists counted, and about three out of every four of these swimming animals can make their own light! To find food, find friends, or startle a hungry hunter!

Archimedes: Bioluminescence. A long word for a fish that brought its own torch.

Professor (telling the story): And here's the most famous fish of the deep: the anglerfish! Her glowing lure works like a fishing rod with a light on the end. Little fish swim up to look... and gulp!

Mei: She's tiny! I thought anglerfish were great big monsters!

Professor: Lots of them are smaller than your hand, Mei! And her light comes from tiny glowing bacteria, living inside the lure.

Professor: Behold! My pretend jellyfish! I made it from a bicycle lamp and a jam-jar lid. All the flashing, none of the wobble!

Professor (telling the story): When some jellyfish are attacked, they flash like a burglar alarm. Scientists think it calls a bigger animal to chase the attacker away. So... let's ring the alarm!

Leo: Something's coming... something really big!

Archimedes (telling the story): It was a giant squid. Its eye was as big as a dinner plate. It looked at us. We looked at it. I hid behind the professor.

Professor (telling the story): A giant squid, as long as a bus, tentacles and all! Hardly anyone has ever seen one alive in its deep-sea home.

Leo: Hello! You're beautiful! Professor... can we keep it?

Archimedes: No. It lives here. And it would not fit in the bath.

Archimedes (telling the story): The giant squid swam away into the dark. Leo waved until it was gone.

Archimedes (telling the story): The professor switched the big lamps back on. And it was snowing. Underwater.

Professor: It's marine snow! Tiny bits of old food and, er, fish poo, drifting slowly down from above. Lots of animals eat it.

Archimedes: That is what the vampire squid eats. Snow. I did say I would explain.

Professor (telling the story): Four thousand metres down, we reached the abyss. In places, great plains of soft mud stretch on into the dark, as cold as a fridge.

Mei: An octopus with ears! I bet I could flap faster than that!

Archimedes (telling the story): Archimedes' Fact File. The dumbo octopus flaps its fins like ears to swim. It is the deepest octopus ever seen: almost seven kilometres down.

Archimedes (telling the story): Then the seabed tipped downhill, into the Mariana Trench: a valley so deep, Mount Everest could hide in it. We sank, and sank, and sank.

Mei: Eight thousand metres! And look, a fish! A little fish, all the way down here!

Professor (telling the story): A snailfish! The deepest fish ever filmed was a snailfish, more than eight kilometres down. Scientists think no fish can live much deeper.

Mei: Nine thousand... ten thousand... ten thousand nine hundred...

Archimedes (telling the story): And then, with a soft little puff of mud and a very loud whistle, we landed. The bottom of the Challenger Deep. The deepest place in the whole world.

Mei: We did it! Nearly eleven kilometres! That's my personal best! And Leo's! And Archimedes'!

Archimedes: I did not ask for a personal best.

Professor (telling the story): Here's an amazing thing! Twelve people have walked on the Moon. But for nearly sixty years, only three people had ever come all the way down here!

Professor (telling the story): And even today, more than seven hundred people have flown into space, but only a few dozen have ever come down here, to the deepest place in the world.

Leo: So that makes us rarer than astronauts?

Archimedes: Much rarer. We are also the first to come in a kettle.

Professor (telling the story): And even here, at the very bottom, there are animals! Little shrimp-like amphipods, and see-through sea cucumbers, searching the mud for scraps from far above.

Mei: Can I open the hatch? I want to touch the bottom!

Professor: Not down here, Mei! Out there, the water squeezes the Kettle from every side, really hard. That's called pressure. Luckily, the Kettle is very, very strong!

Professor (telling the story): On every coin-sized bit of the Kettle, the sea pushes as hard as a big elephant standing on a coin!

Archimedes (telling the story): Archimedes' Fact File. That is also why the blobfish looks blobby. In its deep-sea home, it looks like an ordinary fish. Pulled up to the surface, it goes floppy, like a jelly on a hot day.

Professor: Time to go home! To float up, we just drop our heavy weights, like putting down a big heavy backpack. Up we go!

Archimedes (telling the story): Going up took a very long time. Leo told me about every single animal we had seen. Twice.

Archimedes (telling the story): And then, at last, sunshine.

Mei: Captain Cup! Professor, he's... he's tiny!

Professor: The pressure squeezed him! The tiny bubbles of air in the foam got squashed, so he shrank. That's how hard the deep sea squeezes!

Mei: Sunlight zone, twilight zone, midnight zone, the abyss and the trench! Five zones, nearly eleven kilometres, and one very small cup!

Leo: And I wasn't scared of the dark at all! Well... only a little bit.

Professor: Try this with a grown-up! Ask them to make three small holes, one above the other, up a plastic bottle. Take the lid off and fill it over the sink. The bottom jet squirts out fastest, because it has the most water pressing on it!

Professor: Hardly any of the deep-sea floor has ever been seen. Maybe one day, you'll explore it! Keep asking questions! See you next time with Professor Kettlewick!

Archimedes (telling the story): And I did not rust. Not even a little bit. I checked.