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How Deep is the Ocean?
The dark, mysterious depths of the ocean seem to stretch on forever and ever - but just how deep does it go? And what’s down there? Watch this video to find out, or read our explanation below!
Most of the Ocean is About 3 Miles Deep
The ocean floor goes down slowly the farther it gets away from land, before dropping off the continental shelf. The continental shelf is sort of like a long, sloping hill leading away from the shore, before it drops off like a cliff, down to what’s called the Abyssal Plane. The abyssal plane is the sea floor for most of the ocean. Its fairly flat, and is between 4.000-6.000 meters (2.5 - 3.5 miles) deep.
Trenches in the Ocean Floor
But though the majority of the ocean floor is a similar depth, there are deep trenches in the abyssal plane that go much, much deeper. We’ve only mapped a small portion of the ocean floor, so we can’t yet say for sure what the deepest part is. But the deepest part we’ve discovered so far is the Challenger Deep, which is the deepest part of the already-super-deep Marianas Trench, located in the Western Pacific Ocean.
The Challenger Deep
The Challenger Deep is the deepest known point in the ocean, with a depth of 10,929 meters (35,856 feet). The distance between the Challenger Deep and the surface of the ocean is about the same as the distance between you and an airplane in the sky. It's so deep that if you put Mt. Everest at the bottom of the Challenger Deep, its peak would still be a mile beneath the surface. What’s down there? Sea cucumbers, microorganisms, and plastic trash bags (seriously!).
Ocean Facts for Kids
Got ocean questions? We’ve got ocean answers!
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If you want to put a number on it, scientists estimate there’s about 321,003,271 cubic miles of ocean water.
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The ocean actually gets most of its salt from rivers, which wash away tiny amounts of salt from river beds as they run towards the sea. So, does that mean the ocean is getting saltier? No - because the ocean is also constantly losing salt to sea spray, making salty deposits like salt flats, and other ways.
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The waves you play in at the beach aren’t caused by the Moon, as many people believe. They’re actually caused by wind. Wind blowing over the ocean’s surface for miles and miles can eventually ruffle it enough to push it. That pushed water pushes other water, which pushes other water - in other words, a wave. That wave of energy travels until it’s interrupted, usually by land, which means that the waves you’re swimming in may have originated on the other side of the world.
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The Siphonophore might be the longest creature ever seen. Scientists found one that was 150 feet (46 m) long - half the length of a football field! These strange creatures live deep under the surface, and are as thin as a broomstick. They emit a beautiful, eerie glow, like fireflies, and are actually a colony of thousands of teeny tiny creatures called zooids. The second-longest animal is the lion’s mane jellyfish, which has tentacles up to 120 feet (36 m) long.
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The vast majority of the ocean remains unexplored. Over 80% of the ocean has never been mapped, explored, or even seen by humans. That means there’s lots and lots of unexplored ocean, with creatures left to discover - maybe by you!
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The ocean floor is mapped primarily by using sonar - bouncing sound waves off the bottom of the ocean and measuring how long they take to come back, to figure out how far away it is. Despite technological advances, we’ve still only mapped about 1/20th of the ocean’s floor. So the deepest part of the ocean, the Challenger Deep, may not actually be the deepest part we’ll ever discover.
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Even if the polar ice caps melted, the Earth’s oceans still wouldn’t be able to cover all of Earth. If all of the ice were to melt, the sea level would rise about 230 feet - so everything higher than 230 feet would be above water.
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Scientists have never observed any ways for water to leave the Earth completely. It can cycle through the air, through rivers, into the ground, and even deep underneath the Earth, but the total amount always stays the same.
More Answers to Ocean Questions from Kids
What causes waves? How much water is the ocean? The Tappity Oceanography Library has interactive lessons with answers to those questions and more!
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