What is the Deepest Part of the Ocean?

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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 08 September 2015
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The deepest part of the ocean is the Mariana Trench, an oceanic trench located in the Pacific Ocean near the island nation of Guam. At its deepest point, known as the Challenger Deep, the Mariana Trench is almost 7 miles (11 kilometers) below sea level. Just to put that in a frame of reference, if someone were to shave Mount Everest off the surface of the Earth and drop it into the Mariana Trench, it would disappear, buried in over 1 mile (1.6 km) of water.

As can be imagined, the pressure in the Mariana Trench is extreme: about 1,000 times the atmospheric pressure at sea level. Organisms like humans, who are accustomed to life at sea level, would implode within fractions of a second if exposed to that depth, and the creatures that live in the Mariana Trench demonstrate a number of unusual adaptations which help them cope with the pressure. Algae, bacteria, marine worms, and an assortment of other unusual creatures live in the total darkness and extreme cold, interrupted only occasionally by survey submarines sent to explore the trench for science.


This incredibly deep ocean trench has formed at what is known as a convergent plate boundary. The deepest part of the ocean is formed by the subduction of the Pacific Plate under the Philippine Plate. To get an illustration of what the trench looks like, a person can slide one of his hands under the other. Right along the boundary where the hands meet, a notably deep trough is formed; if this is magnified significantly, it can provide an idea of what this part of the ocean looks like.

The first survey of the Mariana Trench was undertaken in 1951 by a British team on board the Challenger II. Since the team discovered the deepest point of the trench, the Challenger Deep was named after them. A United States Navy bathysphere visited the bottom of the trench in 1960 with two men on board. Oceanographers liken this expedition to the first moon landing, because of the immense amount of preparation and danger involved, and some like to point out that more is known about the surface of the moon than the deepest part of the ocean.

The Mariana Trench isn't the only deep ocean trench, although it is the deepest, extending to twice the average depth of the world's oceans. Given the extreme conditions at the Mariana Trench, it's unlikely that most people will be spending any time there, but if they do, they will be able to see a fascinating array of marine organisms that have only been seen by a handful of human beings.


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Post 15

It's really amazing to spot the deepest part of ocean. Who knows? There may be even deeper spots. But kudos to team for venturing deep. Also I would like to recommend people to the sport of freediving. If you have the guts, give it a go.

Post 12

OK, one more time for those who don't read: Only a very small portion of the ocean floor has been explored; however, roughly 100 percent has been mapped. There's a difference. Same with the Earth's surface: it's been 100 percent mapped, although there still are some places that have yet to be explored.

Post 11

We've mapped most of the world's oceans, even though we've actually looked at a small fraction of the seafloor.

However, all of the deepest spots are in trenches, where one continental plate subducts under another. We know where all the trenches are, and have mapped them in pretty fair detail.

It's not impossible that there could be a deeper spot in one of these trenches, and we could discover it as we get higher resolution maps of the sea floor. However, ocean features vary over a somewhat large scale. It's not like you have a flat bottom at 20,000 feet, and then suddenly a small hole in the middle of the flat area at 40,000 feet. If that

were so, then yes, we could have missed that hole because we weren't looking in fine enough detail.

However, like I said, the topography down there is much more gradual, just like on the surface. On the surface, you wouldn't expect to find a 10 mile tall mountain in the middle of a flat plain. If it existed, it would be where the topography is generally mountainous. You would look for it in a mountain range.

It's the same for the sea floor. The deepest spots are in the trenches, and most trenches have been pretty finely mapped. If there are deeper spots than Challenger Deep, they are probably quite tiny, and not a whole lot deeper.

Post 10

Can we really say that we have seen the deepest part of the ocean yet? The ocean is a depth of wonders and until all of the ocean has been searched then who knows what's under there.

Post 9

If we have only explored 3 percent of the oceans, then how do we know the Marianna Trench is the deepest part of the ocean?

Post 8

We have discovered all of the oceans but have only explored 3 percent of them and by the way, there would be fish poop on the bottom.

Post 6

I wonder if we'll ever know the answer to this.

Post 5

Actually we have discovered about three precent of the ocean.

Post 4

I wonder what would be at the bottom.

Post 3

Just because we have only explored only 1 percent, doesn't mean we haven't mapped the rest.

Post 1

I just have to wonder that if we have only explored 1 percent of our oceans floor, maybe the deepest part of the ocean is still waiting to be discovered.

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