The Deepest Places in the Ocean: Inside the Mariana Trench and Challenger Deep

The deepest measured point on Earth sits 10,935 meters below the surface of the Pacific Ocean — a depth confirmed by a 2020 acoustic measurement study with an uncertainty of just ±6 meters. Stack Everest on the ocean floor at Challenger Deep and its summit would still be submerged by more than 2 km of water above it. The pressure at that depth reaches 1,086 bar (15,750 psi): roughly 1,086 times the air pressure you experience at sea level, concentrated on every surface, in every direction, simultaneously. And yet the first human visitors in 1960 looked out of their porthole and saw a flatfish on the bottom. Life does not stop at the edge of what seems survivable.

The Mariana Trench: Where Tectonic Plates Disappear

The Mariana Trench is a crescent-shaped scar in the western Pacific Ocean, stretching approximately 2,550 km (1,580 miles) in length and averaging 69 km (43 miles) in width. It lies east of the Mariana Islands, roughly 200 km southwest of Guam.

Subduction zone — a tectonic boundary where one plate slides beneath another into the mantle. The seafloor at a subduction zone descends at a steep angle, creating a trench. The Mariana Trench marks where the ancient Pacific Plate slides beneath the smaller Mariana Plate at roughly 2–3 cm per year.

The Pacific Plate subducting here is some of the oldest oceanic crust on Earth — approximately 170–180 million years old, cold and dense from billions of years of cooling. Old, cold oceanic crust is denser than younger, warmer crust, which is part of why it sinks so readily. The trench is the direct surface expression of that descent.

Subduction zones are also where most of Earth's megathrust earthquakes occur — the same class of earthquake that generated the 2011 Tōhoku tsunami and the 2004 Indian Ocean disaster. The Mariana Trench itself is not a major earthquake source at its deepest sections, partly because the stresses at extreme depth are distributed differently than at shallower subduction boundaries.

Source: USGS Earthquake Hazards Program — plate tectonic explanation of subduction zones and the formation of ocean trenches at convergent plate boundaries.

The Top 10 Deepest Ocean Points

Rank	Location	Depth (m)	Ocean	Notes
1	Challenger Deep (Mariana Trench)	10,935	Pacific	Deepest known point on Earth
2	Sirena Deep (Mariana Trench)	~10,809	Pacific	Second deepest, same trench
3	Horizon Deep (Tonga Trench)	~10,816	Pacific	Deepest in Southern Hemisphere
4	Emden Deep (Philippine Trench)	~10,545	Pacific	Deepest in Philippine Sea
5	Romanche Trench	~7,760	Atlantic	Deepest in Atlantic
6	Puerto Rico Trench	~8,376	Atlantic	Deepest point in Atlantic basin
7	South Sandwich Trench	~8,266	Atlantic/Southern	South Atlantic extremity
8	Java Trench (Sunda Trench)	~7,729	Indian	Deepest in Indian Ocean
9	Izu–Ogasawara Trench	~9,780	Pacific	Adjacent to Mariana system
10	Kermadec Trench	~10,047	Pacific	Near New Zealand

Source: NOAA Ocean Exploration — bathymetric data compiled from multibeam sonar surveys. Depths for lesser-measured trenches carry higher uncertainty than Challenger Deep's 2020 figure.

Source: Gardner, J.V. et al. (2014) — bathymetric survey of the Mariana Trench, providing refined depth measurements for Sirena Deep and surrounding areas.

Measuring the Abyss: How We Know the Depth

The current accepted depth of 10,935 ± 6 meters for Challenger Deep was published in 2021 by researchers including Don Walsh (one of the original 1960 divers), drawing on measurements made by Limiting Factor submersible expeditions in 2020. The method combined acoustic altimetry — bouncing sound waves off the seafloor from a known depth — with in-situ pressure sensor readings referenced against oceanographic models of seawater properties at those depths.

Earlier measurements produced different figures precisely because the speed of sound in seawater changes with temperature, salinity, and pressure. Early sonar surveys assumed a constant sound speed and systematically underestimated depth. The 1960 descent by Trieste gave an acoustic measurement of approximately 10,916 meters (35,814 feet). The 1995 Japanese unmanned probe Kaikō measured 10,911 meters. The 2010 USGS survey measured 10,994 meters using ship-based multibeam sonar. The 2020 measurement of 10,935 ± 6 meters incorporated corrections for all of these variables and is considered the most reliable figure to date.

Think of measuring the ocean's depth by sound like measuring the depth of a swimming pool by clapping and listening for the echo — except the speed of sound through the pool changes at every depth because the water's temperature, pressure, and salt content all vary. The correction math is the entire challenge.

Source: Jamieson, A.J. et al. (2021), "Revised depth of the Challenger Deep from submersible transects," Deep-Sea Research Part I, Vol. 177 — the peer-reviewed source for the 10,935 ± 6 m figure. sciencedirect.com

Three Crewed Dives to the Bottom of the World

Only three crewed vehicles have ever reached Challenger Deep. Each descent took place under different technological circumstances and with different scientific objectives.

January 23, 1960 — USS Trieste (Walsh and Piccard). The Trieste was a bathyscaphe — not a submarine, but a vehicle closer in concept to an underwater balloon. A large float filled with aviation gasoline (which is buoyant at depth) provided lift, while iron shot ballast was released to ascend. Lieutenant Don Walsh of the US Navy and Swiss engineer Jacques Piccard descended in a cramped 2-meter-diameter steel pressure sphere attached beneath the float. The descent took 4 hours and 47 minutes. They spent 20 minutes on the bottom before an outer observation window cracked (not the inner sphere) and they ascended. In those 20 minutes, Piccard observed what appeared to be a flatfish — probably a snailfish — through the porthole. The Trieste was subsequently retired without further deep dives.

March 26, 2012 — Deepsea Challenger (James Cameron). Film director James Cameron descended alone in a custom-built, vertically oriented vehicle developed over eight years by a team in Sydney. The Deepsea Challenger reached 10,898 meters — slightly shallower than Challenger Deep's maximum measured point — spending 70 minutes on the bottom. Cameron collected sediment and biological samples. The vehicle was subsequently donated to NOAA and the Woods Hole Oceanographic Institution.

May 1, 2019 — DSV Limiting Factor (Victor Vescovo). American private equity executive Victor Vescovo descended in a purpose-built deep-rated submersible, the DSV Limiting Factor, reaching 10,928 meters — the deepest crewed descent on record at that point. Vescovo completed Five Deeps: the deepest point in each ocean. At Challenger Deep, he spent four hours on the bottom and found a plastic bag and candy wrappers.

Source: NOAA Ocean Exploration — historical account of the 1960 Trieste dive and subsequent crewed expeditions to Challenger Deep.

Source: Vescovo, V. (2019) — Five Deeps Expedition official records, confirmed by Guinness World Records as deepest crewed ocean descent at 10,928 m on May 1, 2019.

Pressure at Depth: The Physics of 1,086 Bar

Atmospheric pressure at sea level is approximately 101,325 pascals, or 1 bar (sometimes expressed as 14.7 psi). Pressure in the ocean increases by roughly 1 bar (14.5 psi) for every 10 meters of depth — simply because the weight of the water column above grows with depth. At 10,935 meters, the pressure is approximately 1,086 bar, or 1,086 times sea-level atmospheric pressure.

What does that mean physically? A foam cup lowered to that depth would compress to approximately the size of a thimble. The air space inside is crushed out and the foam's molecular structure collapses under the load. Wooden items implode. Any gas-filled cavity — a lung, an air bladder — would be crushed instantly.

Metal, however, behaves differently. Steel and titanium can withstand enormous compressive forces. The trick in designing deep-sea pressure vessels is that the sphere geometry distributes the inward force evenly — like an eggshell in reverse, resisting compression from outside rather than from within. The DSV Limiting Factor's personnel sphere is made from titanium approximately 90 mm (3.5 inches) thick.

Water itself is nearly incompressible — at 10,935 meters, seawater is only about 5% more dense than at the surface. This is why the ocean floor has not been crushed by its own pressure: the water column distributes the force through the fluid itself.

Source: NOAA Ocean Exploration — pressure physics explanation for deep ocean environments, noting ~1 atmosphere increase per 10 m of depth.

The Hadal Zone: Life Beyond the Sunlight

Hadal zone — the ocean region below 6,000 meters depth, named for Hades (the underworld in Greek mythology). The zone corresponds to the interior of ocean trenches and constitutes less than 1% of the total ocean floor by area.

The hadal zone is permanently lightless, near-freezing (typically 1–4°C), and subject to pressures that would kill almost any surface organism within seconds. Yet it supports diverse communities of life, shaped by these very conditions into forms that have no equivalents in shallower water.

Amphipods — small crustaceans, typically 1–4 cm long in shallow water — reach body lengths of 30+ cm in the hadal zone of the Mariana Trench. The species Alicella gigantea has been caught at depths exceeding 7,000 meters at lengths of up to 34 cm. Deep-sea gigantism, the tendency for crustaceans to grow larger in deep, cold, food-scarce environments, likely reflects the advantage of larger fat reserves in a nutrient-limited habitat.

Snailfish (Pseudoliparis swirei) were documented at 7,966 meters in the Mariana Trench in 2017, and a separate species (Pseudoliparis belyaevi) in the Japan Trench was recorded at 8,336 meters in 2023 — the deepest fish ever observed. These animals look nothing like the robust fish of surface waters: translucent, gelatinous, and without scales, their tissues are saturated with trimethylamine oxide (TMAO), a pressure-stabilizing molecule that prevents proteins from deforming under compression.

Microbial communities in hadal sediment are extremely dense relative to abyssal (3,000–6,000 m) sediments, likely because organic matter from the water column funnels into trench depressions. These sediments can contain more bacteria per gram than some surface soils.

And plastic waste: Victor Vescovo's 2019 dive found a plastic bag and candy wrappers on the floor of Challenger Deep. Microplastics have been documented in amphipods from six ocean trenches. The deepest place on Earth is contaminated.

Source: Jamieson, A.J. et al. (2017), "Bioaccumulation of persistent organic pollutants in the deepest ocean fauna," Nature Ecology & Evolution — documents synthetic pollutants in hadal amphipods from the Mariana and Kermadec trenches, including PCBs and PBDEs at concentrations exceeding heavily polluted surface environments.

Source: Yancey, P.H. et al. (2014), "Marine fish may be biochemically constrained from inhabiting the deepest ocean depths," Proceedings of the National Academy of Sciences — explains the role of TMAO in stabilizing proteins at high pressure and why fish cannot physiologically exist below approximately 8,200 meters.

The Hadal Zone and Its Deepest Known Ecosystems

The Mariana Trench is not the only hadal zone on the planet. There are approximately 46 hadal trenches and 13 hadal troughs worldwide, each an isolated pocket of extreme environment separated from other trenches by thousands of kilometers of abyssal seafloor. This isolation has driven unique evolution: species assemblages differ between trenches to a degree comparable to fauna on different continents.

The Kermadec Trench northeast of New Zealand (depth approximately 10,047 m) hosts some of the best-studied hadal communities, partly due to New Zealand's oceanographic research programs. The Tonga Trench, one of the deepest after the Mariana system, has produced snailfish observations approaching 9,000 meters.

Food in the hadal zone comes almost entirely from marine snow — the constant rain of organic particles, dead plankton, fecal matter, and other material sinking from surface and mid-water layers. The funnel geometry of trenches concentrates this material: the sloping walls channel falling particles toward the deepest axis, making trench floors food-richer than the surrounding flat abyssal plain at the same depth.

Source: Jamieson, A.J. (2015), The Hadal Zone: Life in the Deepest Oceans, Cambridge University Press — the primary academic reference text on hadal ecology, biogeography, and the biology of organisms adapted to trench environments.

The Biological Limit: How Deep Can Life Actually Go?

The snailfish filmed at 8,336 meters in the Izu-Ogasawara Trench in 2023 looks less like a fish and more like a pale, translucent ghost — no scales, gelatinous body, fins nearly invisible against the sediment. Yet it swims actively, hunts crustaceans, and outcompetes everything around it. The hadal zone, the ocean layer below 6,000 meters, spans roughly 45 individual trenches worldwide and covers less than 0.2% of the seafloor by area. Every expedition that has sampled it has returned with organisms, often in unexpected abundance.

Xenophyophores — single-celled amoebae that can grow to the size of a softball — are among the most striking hadal residents. Researchers from the Scripps Institution of Oceanography documented xenophyophores at 10,641 meters depth in the Sirena Deep of the Mariana Trench in 2011, making them among the deepest multicellular-looking organisms ever observed. They are not multicellular: the entire organism, sometimes 10 cm or more across, is a single cell with multiple nuclei. They function as ecosystem engineers, capturing organic debris and providing surface structure that other hadal species use as habitat.

The snailfish record sits close to what biochemistry permits. Proteins are held in their functional shape partly by weak molecular forces that high pressure systematically disrupts. Organisms counter this with trimethylamine oxide (TMAO), a small organic molecule that acts as a molecular chaperone — it stabilizes protein shapes under compression the way a splint holds a bone. In snailfish, TMAO concentration increases linearly with depth. The problem is osmotic: above a certain TMAO concentration, the molecule starts pulling water into cells faster than the fish can regulate. Research published in PNAS by Paul Yancey and colleagues in 2014 calculated that this osmotic ceiling corresponds to a depth of approximately 8,200–8,400 meters. The 2023 snailfish observation at 8,336 meters sits right at that predicted limit, suggesting we may now have filmed the deepest fish that physics will allow.

Below the fish line, the hadal zone belongs to invertebrates and microbes. Amphipods — small, shrimp-like crustaceans — are the dominant macrofauna, reaching 30+ cm in some hadal trenches compared to the 1–4 cm typical of shallow-water relatives. They appear in enormous densities in baited traps: a single trap deployed at 10,000 meters in the Kermadec Trench can return thousands of individuals. Their bodies accumulate persistent organic pollutants — PCBs, flame retardants, plastic-derived chemicals — at concentrations that can exceed those measured in industrialized coastal bays. The funnel geometry of ocean trenches concentrates not just marine snow and organic matter, but every hydrophobic contaminant that sinks through the water column.

Chemosynthetic communities, the deep-sea ecosystems that run on chemical energy rather than sunlight, are less common in trenches than at hydrothermal vents on mid-ocean ridges. But cold seeps — places where methane and hydrogen sulfide leak from the seafloor — do occur in some hadal settings, supporting chemosynthetic bacteria and the organisms that consume them. These communities demonstrate that photosynthesis is not the only viable base for a food web; in the hadal zone, sunlight is not just scarce — it is completely absent, and life found other paths.

Source: Yancey, P.H. et al. (2014), "Marine fish may be biochemically constrained from inhabiting the deepest ocean depths," Proceedings of the National Academy of Sciences — explains the TMAO osmotic ceiling at approximately 8,200–8,400 meters as the theoretical maximum depth for fish life, a limit subsequently approached by the 2023 Izu-Ogasawara snailfish observation at 8,336 meters.

What People Get Wrong About the Ocean's Depth

The most durable misconception is that the oceans are almost entirely mapped. They are not. As of the mid-2020s, less than 25% of the global seafloor has been mapped at resolution sufficient to identify major features. The seafloor of Mars and the Moon are better mapped, from orbit, than Earth's ocean floor. NOAA's Seabed 2030 project — a global initiative to produce a complete seafloor map by that year — is the primary effort to close this gap.

A second misconception: the Mariana Trench as a featureless slot. It is not flat. The trench floor at Challenger Deep contains at least three distinct depressions — eastern, western, and central pools — each deeper than 10,850 meters. The walls rise steeply and include geological features such as fault scarps and sediment channels.

Third: that pressure in the deep ocean would "crush" a human body beyond recognition. In fact, the human body contains little air space (mainly the lungs, sinuses, and middle ear) — the major injury mechanisms are barotrauma to those spaces, not wholesale compression of the solid body. An unprotected human body sinking to Challenger Deep would implode at the lung-tissue boundary and drown long before reaching notable depth. The tissues themselves, being mostly water, are largely incompressible.

For a comparison of Earth's most extreme environments at both ends of elevation, see our coverage of the tallest mountains on Earth.

Frequently Asked Questions

Q: How deep is the Mariana Trench's Challenger Deep exactly?
A: The most precise measurement to date, published in 2021, places the deepest point of Challenger Deep at 10,935 ± 6 meters (35,876 ± 20 feet) below sea level. This was determined using acoustic altimetry from the DSV Limiting Factor submersible, corrected for seawater temperature, salinity, and pressure gradients.

Q: What is the water pressure at the bottom of Challenger Deep?
A: Approximately 1,086 bar, or 15,750 psi — roughly 1,086 times the atmospheric pressure you experience at sea level. This is equivalent to the weight of 50 jumbo jets pressing on every single square meter of surface.

Q: Has anything lived at the bottom of the Mariana Trench?
A: Yes. Every crewed and unmanned expedition to Challenger Deep has found biological activity. Documented life includes amphipods (crustaceans), snailfish, sea cucumbers, polychaete worms, foraminifera, and dense microbial communities in the sediment. Life at the bottom of the ocean is not exceptional — it is the rule.

Q: Why can't submarines simply go to the deepest parts of the ocean?
A: Standard military and research submarines are rated to depths typically between 300 and 600 meters. The pressure at Challenger Deep (1,086 bar) is roughly 100 times greater than even deep-rated military submarine operating depths. Building a vehicle that can withstand this pressure while maintaining internal habitable conditions requires specialized titanium spheres and engineering that most submarine programs never pursue.

Q: Who has been to the bottom of Challenger Deep?
A: As of 2025, fewer than 30 people have reached Challenger Deep. Don Walsh and Jacques Piccard made the first descent in 1960 aboard the Trieste. James Cameron descended solo in 2012. Victor Vescovo reached the record depth of 10,928 m in 2019 and led subsequent dives that took additional scientists and crew members to the bottom aboard the DSV Limiting Factor.

Q: Is there plastic at the bottom of Challenger Deep?
A: Yes. Victor Vescovo reported seeing a plastic bag and candy wrappers during his 2019 dive. A 2019 study by Jamieson et al. in Nature Ecology & Evolution documented synthetic fibers and microplastics inside the gut contents of amphipods collected from six ocean trenches, including the Mariana. The concentration of some persistent organic pollutants in trench amphipods exceeded levels measured in heavily industrialized coastal regions.

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