The Mariana Trench is the deepest known place in any ocean on Earth. It is a crescent-shaped trench in the western Pacific Ocean, east of the Mariana Islands, and its lowest point — the Challenger Deep — sits roughly 10,935 metres (35,876 feet) below sea level. That figure comes from pressure sensors carried by a crewed submersible in 2020 and is precise to about ±6 metres (Greenaway et al., Deep-Sea Research Part I, 2021).
One correction worth making at the top, because it is repeated almost everywhere online: the Mariana Trench is not the deepest ocean. It is a trench — a narrow scar cut into the floor of the Pacific Ocean by one tectonic plate sliding beneath another. The Pacific is the deepest ocean; the Mariana Trench is the deepest thing in it.
The trench exists because two tectonic plates converge here. The Pacific Plate is forced beneath the Mariana Plate, and the seafloor bends sharply downward along the contact to form the trench.
Many sources say the Pacific Plate subducts beneath the Philippine Sea Plate instead, and that is worth untangling because this article used to say both. The Mariana Plate is a small plate that was once part of the Philippine Sea Plate and split away from it as the Mariana Trough back-arc basin opened behind the island arc. Older and simplified accounts still lump the two together. The plate actually overriding the Pacific Plate at the trench today is the Mariana Plate.
Two numbers explain why the place is so hard to reach. At the bottom of the Challenger Deep the water column presses down at about 1,086 bar — roughly 15,750 pounds per square inch, or eight tons on every square inch, about 1,071 times the atmospheric pressure you are sitting in now. And if you dropped Mount Everest (8,849 m) into the Challenger Deep, its summit would still be more than 2,000 metres underwater.
Everything below 6,000 metres is called the hadal zone, named after Hades. It accounts for only a sliver of the ocean floor, and the Mariana Trench contains the deepest part of it. The organisms found there — amphipods, xenophyophores, snailfish and pressure-loving (piezophilic) bacteria — are adapted to cold, permanent darkness and crushing pressure. See what actually lives in the Mariana Trench for the species themselves.
Research within the Mariana Trench sheds light on the unique ecosystems at such depths and contributes to our understanding of Earth’s geological processes. Further exploration of the Mariana Trench reveals new species and valuable information about our planet and its vast underwater ecosystems.
What is the Mariana Trench?
The Mariana Trench is the deepest known part of the world’s oceans. Its floor at the Challenger Deep lies about 10,935 metres (35,876 feet) down — just under 11 kilometres, or about 6.8 miles. It is a crescent-shaped trench in the western Pacific Ocean, formed where the Pacific Plate subducts beneath the smaller Mariana Plate.
Why sources give different depths
Search for the depth of the Mariana Trench and you will be handed 10,924 m, 10,935 m, 10,984 m, 10,994 m and a round 11,000 m, often on the same page. They are not typos. They are different measurements taken by different instruments, and the difference between them is smaller than it looks.
| Measurement | Depth | Method | Year |
|---|---|---|---|
| Greenaway et al., Deep-Sea Research I | 10,935 m ± 6 m (35,876 ft) | Pressure sensors on crewed submersible transects, gravity-corrected | 2021 |
| Bongiovanni et al., Geoscience Data Journal | 10,924 m ± 15 m (35,840 ft) | Kongsberg EM124 multibeam sonar, Five Deeps Expedition | 2022 |
| Vescovo dive, DSV Limiting Factor | 10,928 m (35,853 ft) | Deepest depth actually occupied by a crewed vehicle | 2019 |
| HMS Challenger sounding | 4,475 fathoms (8,184 m) | Weighted hemp sounding line | 1875 |
Sonar measures how long a sound pulse takes to return, so it depends on knowing the speed of sound through ten kilometres of water of varying temperature and salinity. A pressure sensor on a submersible sitting on the bottom measures the weight of the water column directly, but has to be corrected for local gravity. The two methods now agree to about a tenth of a percent, which is why 10,935 m is the figure this article uses throughout.
Location
The trench runs for about 2,550 kilometres (1,580 miles) in an east-southeast to west-northwest arc, with a mean width of about 69 kilometres (43 miles), according to NOAA’s National Centers for Environmental Information. It sits east of the Mariana Islands, and the Challenger Deep lies roughly 322 kilometres (200 miles) south-west of Guam.
Note the shape of those numbers: the trench is roughly 37 times longer than it is wide, and only about 11 kilometres deep at its lowest point. Cross-sections like the one below exaggerate the vertical scale enormously. In true proportion the Mariana Trench is a very long, very shallow crease — not the vertical chasm most illustrations show.
How old is the Mariana Trench?
This is where a very common error creeps in. The Mariana Trench is routinely described as having formed 180 million years ago in the Jurassic. That number is real, but it is the age of the seafloor being swallowed, not the age of the trench.
Subduction in the Izu-Bonin-Mariana system actually began about 52 million years ago, in the early Eocene. That date is not an estimate from surface geology — it comes from drilling into the forearc itself during International Ocean Discovery Program Expeditions 351 and 352, which recovered the basalts and boninites erupted as the subduction zone switched on.
The two numbers together are what explain the depth. The Pacific crust entering the Mariana Trench is Jurassic — among the oldest oceanic crust on Earth, and therefore the coldest and densest. Old, cold, heavy crust sinks steeply and pulls the trench down with it. A young, warm plate would subduct at a shallower angle and never cut this deep. The Mariana Trench is the deepest place on Earth largely because it is consuming the planet’s oldest seafloor.
Depth and Formation
The Mariana Trench is the deepest trench in any ocean, bottoming out at about 10,935 metres (35,876 feet) in the Challenger Deep. It lies in the western Pacific Ocean, east of the Mariana Islands, which is where it gets its name. The trench marks the boundary where the Pacific Plate is being driven beneath the Mariana Plate.
The trench is the surface expression of subduction. The Pacific Plate bends and descends beneath the Mariana Plate at an unusually steep angle — close to vertical at depth — and the seafloor is dragged down along the hinge. This steep dip is the second reason the Mariana Trench outruns every other trench on Earth.
As the descending plate bends downward it creates the deep depression called a hadal trench — the class of trench that reaches past 6,000 metres. There are only a few dozen such trenches on Earth, almost all of them ringing the Pacific along the Ring of Fire, and the Mariana Trench is the deepest of them all.
The trench has kept evolving since it formed, and its shape today is the product of about 52 million years of continuous subduction. The Mariana Trough, the back-arc basin behind the island arc, is far younger still — it opened as the Mariana Plate rifted away from the Philippine Sea Plate, which is why the two plates are so often confused in older write-ups.
The trench features unique bathymetric and geomorphological characteristics due to the various factors that affect its formation. For example, the depths of the trench can vary significantly along its length, with the Challenger Deep being the deepest known point. Factors influencing the depth and development of the trench include the age and temperature of the tectonic plates, as well as the local and regional geological structures.
Depth, plate age and dip therefore all point the same way: the Mariana Trench is not deepest by accident. It is where the oldest, coldest seafloor on the planet is being pulled down at the steepest angle.
See Related: Types of Terrain You Need to Know
Physical Characteristics
The Mariana Trench, in the western Pacific Ocean, is the deepest oceanic trench on Earth. It descends to about 10,935 metres (35,876 feet) at the Challenger Deep, stretches roughly 2,550 kilometres (1,580 miles), and averages about 69 kilometres (43 miles) wide.
The trench owes its distinctive V-shaped profile to subduction, in which the denser Pacific Plate sinks beneath the lighter Mariana Plate. The extreme depth and pressure produce physical and chemical conditions found almost nowhere else, which is why the trench draws so much research attention.
Sediments that accumulate on the trench floor are mostly clay, biogenic siliceous and calcareous materials, and volcanic ash, which significantly impact the physical and mechanical properties of deep oceanic sediments in the trench. The mineral composition of the sinking particles and the changes in their seasonal and depth distribution give important clues about the provenance and sedimentary characteristics of this unique environment.
Far below the thermocline, water in the trench stays just above freezing, roughly 34 to 39 degrees Fahrenheit (1 to 4 degrees Celsius). Pressure rises by about one atmosphere for every 10 metres of depth, so by the floor of the Challenger Deep it reaches around 1,086 bar (15,750 psi). Sunlight is gone entirely below about 1,000 metres, so the bottom of the trench has been in permanent darkness for its whole existence.
That pressure is the engineering problem. The viewport of a full-ocean-depth submersible has to hold back roughly eight tons on every square inch, and a hull failure at that depth is instantaneous.
Due to its depth, location, and tectonic origins, the Mariana Trench boasts unique physical characteristics. The trench’s distinct geological features, harsh environmental conditions, and sedimentary composition continue to intrigue researchers as they strive to unravel the mysteries of this extraordinary underwater world.
See Related: What Lives In The Deepest Part of the Ocean? 7 Incredible Mariana Trench Animals
Scientific Expeditions
Due to its unique geological and ecological features, the Mariana Trench, located in the western Pacific Ocean, has been the subject of ocean exploration and numerous scientific expeditions. In 2016, China conducted a major 10,000-meter hadal trench expedition, which led to the discovery of ferromanganese deposits and provided insights into the geochemical manganese cycle in the trench’s sedimentary environments.
During the same year, another expedition involving the deployment of two hadal landers, Tian Ya and Hai Jiao, took place from June 22nd to August 12th. These landers conducted various scientific tasks, including collecting samples and capturing footage. This successful mission allowed for further assessment of the Mariana Trench’s deep-sea environment, providing valuable data for future investigations.
In continuance of this research, China conducted its third Mariana Trench scientific expedition, which involved the application of the Haidou Autonomous and Remotely-operated Vehicle (AROV). This advanced technology allowed for in-depth exploration and sample collection in the trenches, furthering the understanding of the geological and ecological features present.
During these expeditions, a focus on sampling deep-sea creatures from the hadal trenches was apparent, as there was a need for a better understanding of the life present in such extreme environments. As a result of deep-sea research, researchers developed a novel pressure-retaining sampler to capture amphipods at these extreme depths. This groundbreaking technology was field-tested during a science expedition cruise in the Mariana Trench.
In addition to ecological research, the Mariana Trench has been the subject of studies focused on understanding the geochemistry of rocks found in the area. For instance, one such expedition analyzed basaltic and gabbroic rocks collected from the West Mariana Basin and the Mariana Trench itself. This analysis contributed valuable information to the International Geological Correlation Program (IGCP) project known as “Ophiolites.”
Throughout these scientific expeditions, researchers have gained much knowledge regarding the natural ecology of Mariana Trench’s geological and ecological features. This understanding is crucial for developing a comprehensive view of the unique deep-sea environment found in the Mariana Trench and its potential impact on the broader earth system.
See Related: Different Types of Ecosystems Around the World
Who Has Been to the Bottom of the Mariana Trench?
Fewer than 30 people have reached the floor of the Challenger Deep. More people have stood on the summit of Everest in a single morning.
| Date | Who | Vehicle | Note |
|---|---|---|---|
| 23 Jan 1960 | Jacques Piccard, Don Walsh | Bathyscaphe Trieste | First crewed descent. A cracked outer window pane ended the visit after about 20 minutes. |
| Mar 2012 | James Cameron | Deepsea Challenger | First solo dive, and the first return in 52 years. |
| 28 Apr 2019 | Victor Vescovo | DSV Limiting Factor | 10,928 m — deepest crewed dive on record. |
| 2019–2022 | Victor Vescovo | DSV Limiting Factor | 15 separate visits, a Guinness World Record. |
The 59-year gap between Piccard and Cameron is the striking part. Between 1960 and 2012 the deepest place on the planet went unvisited by humans, while twelve people walked on the Moon.
Who Owns the Mariana Trench?
Nobody owns the trench outright, but the common answer that it lies in international waters is wrong.
A large part of the trench falls inside the United States exclusive economic zone around Guam and the Commonwealth of the Northern Mariana Islands. On 6 January 2009, Presidential Proclamation 8335 established the Marianas Trench Marine National Monument, protecting about 95,216 square miles across three units:
- The Trench Unit — the submerged lands of the trench itself, roughly 1,100 miles long and 44 miles wide. The water column above it is not included.
- The Volcanic Unit — submerged lands around 21 undersea mud volcanoes and hydrothermal vents along the Mariana Arc.
- The Islands Unit — the waters and submerged lands around the three northernmost Mariana Islands: Farallon de Pajaros (Uracas), Maug and Asuncion.
There is a twist worth knowing. The Challenger Deep is not inside the monument. It sits about 9 kilometres beyond the boundary, within the exclusive economic zone of the Federated States of Micronesia. The deepest point on Earth is therefore under Micronesian jurisdiction, not American, and not unclaimed.
The National Oceanic and Atmospheric Administration co-manages the monument with the US Fish and Wildlife Service. Rights over the seabed and water column in all of these zones flow from the United Nations Convention on the Law of the Sea.
See Related: Hydrothermal Vents: How Life Survives Without Sunlight
Sources
- Greenaway, S.F. et al. (2021). Revised depth of the Challenger Deep from submersible transects. Deep-Sea Research Part I, 178, 103644.
- Bongiovanni, C., Stewart, H.A. & Jamieson, A.J. (2022). High-resolution multibeam sonar bathymetry of the deepest place in each ocean. Geoscience Data Journal, 9(1).
- International Ocean Discovery Program, Expedition 352: Izu-Bonin-Mariana Fore Arc (subduction initiation circa 52 Ma).
- NOAA National Centers for Environmental Information, Planet Postcard: The Mariana Trench (dimensions).
- NOAA Fisheries, Mariana Trench Marine National Monument; Presidential Proclamation 8335 (6 January 2009).
- Guinness World Records, Most times to visit the Challenger Deep by an individual.
Frequently Asked Questions
How deep is the Mariana Trench?
The Mariana Trench reaches about 10,935 metres (35,876 feet) below sea level at its deepest point, the Challenger Deep. That figure is precise to roughly ± 6 metres and comes from pressure sensors carried on crewed submersible transects in 2020, published by Greenaway and colleagues in Deep-Sea Research Part I (2021). Multibeam sonar mapping by the Five Deeps Expedition gave a closely comparable 10,924 ± 15 metres. Older figures of 10,984 m, 10,994 m and a round 11,000 m are still widely quoted but have been superseded.
What is at the bottom of the Mariana Trench?
The bottom of the Mariana Trench is a relatively unexplored environment that experiences extreme pressure and darkness. Some organisms, including deep-sea fish, microorganisms, unique worms, and crustaceans, can survive in these harsh conditions. These creatures have adapted to the high pressure and lack of sunlight near the Mariana Islands by developing specialized mechanisms and features.
Has anyone reached the bottom of the Mariana Trench?
Yes, though fewer than 30 people have ever done it. The first crewed dive to the Challenger Deep was on 23 January 1960, when Jacques Piccard and US Navy Lieutenant Don Walsh took the bathyscaphe Trieste to the bottom. No one repeated it for 52 years, until filmmaker James Cameron made a solo dive in Deepsea Challenger in March 2012. The deepest crewed dive on record was made by Victor Vescovo on 28 April 2019, reaching 10,928 metres (35,853 feet) in the submersible Limiting Factor; Guinness World Records credits him with 15 separate visits to the Challenger Deep between 2019 and 2022. Uncrewed landers and remotely operated vehicles have visited many more times.
How was the Mariana Trench formed?
The Mariana Trench was formed by subduction, a process that occurs when two of the Earth’s tectonic plates meet, with one plate being forced beneath the other. In the case of the Mariana Trench, the Pacific Plate was forced under the Mariana Plate. As the Pacific Plate descends, it creates a trench in the ocean floor, which becomes deeper as the process continues over millions of years.
When was the Mariana Trench discovered?
The trench was discovered on 23 March 1875 by the HMS Challenger expedition, which recorded a sounding of 4,475 fathoms (about 8,184 metres) using a weighted hemp line. The depth was so unexpected that the crew sounded a second time to check it. Command is often misattributed to Sir George Nares, who captained Challenger only until late 1874 before leaving to lead the British Arctic Expedition; the ship was under Frank Tourle Thomson at the time of the sounding. The Challenger Deep is named after the ship.
Which country owns the Mariana Trench?
No country owns the trench outright, but it is not simply international waters either, which is the version usually repeated online. Much of the trench lies within the United States exclusive economic zone around Guam and the Commonwealth of the Northern Mariana Islands, and its submerged lands there were protected in 2009 as the Mariana Trench Unit of the Marianas Trench Marine National Monument, created by Presidential Proclamation 8335 and covering about 95,216 square miles across three units. The Challenger Deep itself sits roughly 9 kilometres outside the monument boundary, inside the exclusive economic zone of the Federated States of Micronesia. Coastal-state rights over the seabed and water column in these zones are set by the United Nations Convention on the Law of the Sea.
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