Time To Read
Date Last Modified
The Ocean in Seven Places · Place 04
The Ridge and the Trench
The longest mountain range on Earth is underwater, and in 1950 nobody knew it ran all the way around the planet. At the other end of the same system, the seafloor goes back inside the Earth.
Seven short chapters · about 15 minutes each · a practice set at the end of every chapter
Start here
What you are walking into
Seven short chapters. Each one has a video, a few pictures, something to play with and a quick activity, and very little reading. The first four follow the seafloor itself: how anyone mapped a place nobody could see, why the ocean floor turns out to be young, where it disappears back into the Earth, and what happens when it snaps. You have already met one piece of it: the Nazca Plate that carries the Galápagos east is heading for the Peru–Chile Trench.
The last three go down. At the bottom of the deepest trench the water presses with more than 1,000 times the pressure you feel right now. On the ridges there are hot springs where whole food webs run without sunlight, first found in 1977 near the Galápagos. And the mud on the seafloor turns out to be a history book, and possibly a mine. By the end you will know more about the bottom of the ocean than most people know about the top. You will also have learned a fair amount of college marine geology. We are still not making a big deal of that.
Before you start
Watch this first
Insider Tech — This Incredible Animation Shows How Deep The Ocean Really Is. Three and a half minutes of sinking. No notes, no questions. Just feel how far down the bottom is.
And then this: the ridge on dry land
Tom Scott — Swimming between two continents, debunked. In Iceland the Mid-Atlantic Ridge comes up for air, and people pay to snorkel in its cracks. Tom Scott explains, patiently, why it is not quite what the brochure says.
The seven chapters
Your route to the bottom of the sea
Chapter 1
Mountains Nobody Saw
A ship shouts at the seafloor and waits for the echo. Do that enough times and a hidden mountain range 65,000 km long appears.
Chapter 2
The Seafloor Is Young
The rocks of the ocean floor remember which way north used to be, and the stripes they make prove the seafloor is moving.
Chapter 3
Where the Seafloor Goes Back In
Where plates collide, old seafloor dives back into the Earth and digs a trench deep enough to hide Mount Everest.
Chapter 4
When the Seafloor Snaps
When a stuck plate lets go, a wave that ships barely notice races across the Pacific at the speed of a jet.
Chapter 5
The Weight of the Water
Every 10 m down adds the weight of another whole atmosphere. At the bottom of the Challenger Deep, that is more than 1,000 of them.
Chapter 6
Life Without the Sun
In 1977 a submarine full of geologists found clams, crabs and giant worms living on hot springs, with no sunlight at all.
Chapter 7
What the Mud Remembers
The deep seafloor is buried under a slow snow of shells, dust and metal, and it has been taking notes for millions of years.
Photos: Kindel Media, Dương Nhân, Lucas Valentim, Ray Bilcliff, Blaque X, Attila Pergel, Magda Ehlers / Pexels
Play with it
Stand on the Mid-Atlantic Ridge
Almost all of the mid-ocean ridge is underwater, but in Iceland it comes up for air. This 3D model is Þingvellir, a valley in Iceland where the North American and Eurasian plates are pulling apart by about 2 cm a year. Drag to spin it and look for the long cracks and cliffs: that is seafloor spreading, happening on dry land.
3D model: “Þingvellir, Iceland” by Sara Carena on Sketchfab (CC BY-NC).
How to use these pages
Watch it, read it, try it
Every chapter has the same rhythm: a video, three short cards, something live to explore, and a couple of hands-on activities. The last activity on each page is an eight-question practice set that covers the whole chapter. Do every one, retry anything you miss, and read the feedback. The wrap-up page ends with a twenty-question review of the whole seafloor.
Warm-up
What do you already know?
Six true-or-false guesses before you start. Getting some wrong right now is the point: each answer tells you which chapter explains it.
Ready?
Chapter 1 is fifteen minutes and mostly pictures
Photo credits (Pexels): Diego F. Parra, Arjanne Holsappel, Kindel Media, Dương Nhân, Lucas Valentim, Ray Bilcliff, Blaque X, Attila Pergel, Magda Ehlers.