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Oceanic Trench

Oceanic trenches are long, V-shaped depressions in the ocean floor. They are the deepest part of the ocean, home to the lowest points on Earth. 

A 3D illustration of what it looks like under the surface of the ocean.

Oceanic trenches are deep under the ocean!

Oceanic trenches are the markings of plate boundaries. They are a result of the subduction of plates. They can extend for thousands of kilometers. These trenches change over time because the tectonic plates keep moving. 
 

The Making of a Trench

When heavy, flexible oceanic crust starts to descend into the asthenosphere, oceanic trenches form. The seaward side of the trench possesses a slop of 5 degrees. This is because the plate needs to bend as it dives downward. The inner wall of the trench forms on the continental side. The wall a slope between 10 and 16 degrees. These two plates will glide past one another at the bottom of the trench where they intersect. 

An illustration of an oceanic trench caused by subduction.

Trenches are a result of plate tectonics

The Mariana Trench

Deep in the Pacific Ocean is the Mariana Trench, the deepest part of the ocean. The Mariana trench is about 36,000 feet deep. It hard to picture exactly how deep that is but think about how far you would get if you walked for about two hours. You’d get pretty far, right?
 
Well, that is about how deep the Mariana Trench is. Mt. Everest is 29,029 feet high if we put Mt. Everest in the Mariana trench the top of the mountain wouldn’t even come close to the surface. 
 

A Dark, High-Pressure Environment 

This part of the ocean is so deep that for a long time scientists didn’t believe any animals lived there. It’s easy to understand why. When you get that far down into the ocean it is hard for anything to survive. For one thing, it’s very dark because the light from the sun can’t get through all that water. Almost every living thing depends on planbts which need sunlight to live.
 
It is also super cold! How cold is it? If it got even a little colder at the bottom of the trench, the water would freeze. On top of everything else, there is a lot of pressure down there. Pressure is what happens when something pushes on something else.
 
Now, when you wash your hands it may not seem like water weighs very much. But if you were under 36,000 feet of water there is a ton of pressure! That’s so much pressure that it isn’t safe for people or any other living thing. Between the cold, the dark, and the pressure it is very hard for anything to survive at the bottom.
 

What Lives in the Mariana Trench?

However, there are some very unique life forms that can live there. With the development of technology, scientists are able to explore the Mariana Trench. They have seen some of the life at the bottom of the ocean, like amphipods. We have amphipods in other parts of the world, they are about 1cm long, roughly the size of a fingernail.
 
The amphipods at the bottom of the trench, however, are 20 cm long, about the size of a grownups hand. Big difference! There are other life forms as well and they all have something in common. They are soft, with no skeletal system. They can’t have bones because the pressure would crush them. 

An image of an amphipoda.

A picture of an amphipod taken with a microscope.

This pressure still makes it very hard for us to explore the Mariana Trench so there is a lot that we don’t know about it. Humans have only managed to explore 5-10% of the ocean. Most of it is still a great mystery.

Other Great Resources:

(Video) Deepest Part of The Ocean: 14 Amazing facts about the Mariana Trench by Wondermins https://www.youtube.com/watch?v=J6MgrUC3BOk

(Video) Long Way Down: Mariana Trench by National Geographic: https://www.youtube.com/watch?v=Y2tm40uMhDI

(Video) How Deep The Ocean Really Is by Tech Insider: https://www.youtube.com/watch?v=UwVNkfCov1k

 

Written by: Monica Siegenthaler