The deepest part of the ocean is the Challenger Deep, at the southern end of the Mariana Trench in the western Pacific Ocean. According to NOAA, the Challenger Deep is about 10,935 meters (35,876 feet) deep, nearly 11 kilometers or almost 7 miles below the surface.
That is more than 2 kilometers deeper than Mount Everest, at 8,848 meters, is tall. If you set Everest on the floor of the Challenger Deep, its peak would still be well under water.
Key facts about the Mariana Trench
- Deepest point: Challenger Deep, about 10,935 m (35,876 ft) deep (NOAA)
- Location: western Pacific Ocean, several hundred kilometers southwest of Guam
- Size: a crescent about 2,550 km long and 69 km wide
- How it formed: the Pacific Plate sinks beneath the Mariana Plate (subduction)
- Pressure at the bottom: about 1,086 bar, roughly 1,070 times the air pressure at sea level
- Water temperature at the bottom: about 1 to 4 °C
- First people at the bottom: Jacques Piccard and Don Walsh in the bathyscaphe Trieste, 23 January 1960
- Average ocean depth, for comparison: about 3,682 m (12,080 ft)
Sources: NOAA Ocean Service, Mariana Trench and Challenger Deep on Wikipedia.
Exploring the depths
Mariana Trench: the frontier of depth
The Mariana Trench is the deepest known part of Earth’s oceans. It curves through the western Pacific for about 2,550 km and is about 69 km wide, running past the Mariana Islands and Guam.
Challenger Deep: the deepest known point
The Challenger Deep is a small, slot-shaped valley in the floor of the trench. It is named after the British ship HMS Challenger, whose crew first sounded the depths of the trench in 1875. Measuring it is hard, and different expeditions have reported slightly different numbers, but they all land close to 10,900 meters. A 2021 study using pressure readings from crewed dives gave 10,935 meters, plus or minus 6 meters, which is the figure NOAA uses.
The closest land is Fais Island in Micronesia, about 155 nautical miles to the southwest, with Guam about 164 nautical miles to the northeast.
Historic descents into the abyss
The first descent to the Challenger Deep took place on 23 January 1960. Jacques Piccard and US Navy Lieutenant Don Walsh reached the bottom in the bathyscaphe Trieste and reported a seafloor of fine ooze.
On 26 March 2012, filmmaker James Cameron made a solo dive in the Deepsea Challenger. His descent took 2 hours and 36 minutes and his sub recorded a depth of 10,908 meters on touchdown.
From 2019, the submersible DSV Limiting Factor carried out repeated crewed dives to the Challenger Deep, which is where much of the latest depth data comes from.
The science of the deep
Ocean trenches and tectonic plates
Ocean trenches form where tectonic plates meet. At the Mariana Trench, the old, heavy Pacific Plate slides beneath the Mariana Plate, a process called subduction. As the plate sinks, it drags the seafloor down into a deep valley.
Water carried down with the sinking plate helps melt rock deeper in the mantle. That melt rises to feed the volcanoes of the Mariana Islands. The same grinding of plates makes the region prone to earthquakes.
Pressure and temperature
At the bottom of the trench, the water above presses down with about 1,086 bar. That is roughly 1,070 times the air pressure we feel at sea level, or about eight tons on every square inch.
The water there is cold, about 1 to 4 °C, and completely dark. Near hydrothermal vents elsewhere in the region, the water can be far hotter.
Life in the deepest ocean
The trench lies in the hadal zone, the part of the ocean deeper than about 6,000 meters. Despite the pressure, cold and darkness, life is found all the way down.
Single-celled organisms called xenophyophores, part of a group known as monothalamea, have been found at about 10.6 km down. The Japanese Kaiko probe and later dives filmed sea cucumbers, scale worms and shrimp-like animals near the bottom, and amphipods are common scavengers at hadal depths.
Fish do not reach the very bottom. The Mariana snailfish, discovered in 2014, was filmed in 2017 at 8,178 meters, one of the deepest fish ever recorded. Many deep-sea creatures are small, pale and slow moving, which helps them survive where food is scarce.
Human interaction and impact
The deepest parts of the ocean remain largely unexplored. Submersibles and ROVs can withstand the pressure and cold, letting scientists observe and sample the seafloor. Ships map trenches with sonar, using sound echoes to measure depth.
Pollution has reached even these depths. In 2019, explorer Victor Vescovo reported a plastic bag and candy wrappers at the bottom of the trench, and amphipods from deep trenches have been found with synthetic particles in their stomachs.
Protecting the Mariana Trench
In 2009 the United States created the Mariana Trench Marine National Monument, covering the parts of the trench inside US waters. The Challenger Deep itself is not included, because it lies in the waters of the Federated States of Micronesia.
Pollution, climate change and the possibility of deep-sea mining are the main concerns for these remote ecosystems, which scientists are only beginning to understand.
Comparison with other trenches
The Puerto Rico Trench is the deepest part of the Atlantic Ocean. Its deepest point, known as the Milwaukee Deep, has been measured at about 8,376 meters. That is more than 2.5 km shallower than the Challenger Deep.
Myths of the deep
Because so little of the deep ocean has been seen, it has long fed legends. Sailors told of the Kraken, a sea monster big enough to drag ships under, a story likely inspired by real giant squid. Others imagined the lost city of Atlantis resting on the seafloor.
Frequently asked questions
What is the deepest part of the ocean?
The Challenger Deep, at the southern end of the Mariana Trench in the western Pacific. NOAA gives its depth as about 10,935 meters (35,876 feet).
How deep is the Mariana Trench in miles?
Its deepest point is about 10,935 meters, which is close to 6.8 miles.
Where is the Mariana Trench located?
In the western Pacific Ocean, curving past the Mariana Islands and Guam. The Challenger Deep lies several hundred kilometers southwest of Guam.
Has anyone been to the bottom of the Mariana Trench?
Yes. Jacques Piccard and Don Walsh reached the Challenger Deep in the Trieste in 1960, and James Cameron dived there alone in 2012. Several more crewed dives followed from 2019.
What lives at the bottom of the Mariana Trench?
Single-celled xenophyophores, amphipods, sea cucumbers, scale worms and microbes. The deepest fish, such as the Mariana snailfish, live a few kilometers higher, around 8,000 meters.