The pressure at the bottom of the Mariana Trench reaches about 8 tons per square inch, and sunlight never arrives there. In 2018, researcher Shiba avoided the ocean entirely and searched through video archives instead, examining recordings from 5,010 old dives that no one had previously studied in detail. One scene from 1998 stopped her completely.
The HMS Challenger, a British Royal Navy survey ship, first discovered the trench on March 23, 1875, by lowering a weighted rope. The rope continued to unspool, producing a reading of approximately 8,184 meters. The crew confirmed the measurement with a second survey at the same location. That expedition was part of a larger four-year voyage that circled the globe to systematically collect oceanographic data, and the team did not realize it had found the deepest place on the planet. The crew simply recorded the number and moved on, leaving later researchers to recognize its significance.
Every measurement since then has pushed the known depth deeper as instruments improved, from weighted ropes to sonar pulses and then to satellite-corrected pressure sensors placed directly on the seafloor. In October 2010, a US Navy survey ship measured the bottom from the surface at 10,994 meters. The most accurate figure comes from June 2020, when Victor Vescovo completed six transects across the deepest basins in the submarine Limiting Factor, accompanied by three autonomous landers, and cross-checked multiple independent pressure readings taken directly at depth rather than relying only on sonar from a ship far above. Those pressure sensors identified the deepest observed seafloor at 10,935 meters, plus or minus 6 meters. That equals 35,876 feet, about 2,000 feet less than the 38,000-foot figure that sometimes circulates online. The gap indicates an inflated number not based on any actual measurement.
Water pressure increases by roughly one atmosphere for every 10 meters of descent. At the bottom of Challenger Deep, that means approximately 16,000 pounds per square inch, about a thousand times the pressure felt at sea level.
The first vehicle to reach the bottom was the Trieste in 1960, a bathyscaphe with a steel sphere featuring 5-inch-thick walls and room for two men in a space 38 inches wide. The two crew members endured the cramped, cold environment for the five hours the entire trip took. Building something that survives that environment is one challenge, and recovering usable footage is another. The solution turned out to be surprisingly low-tech.
Most footage of deep ocean floors has not been captured by piloted submarines. It comes from landers, which are frames carrying weights, floats, lights, and cameras, often with baited traps. Researchers drop them from the back of a ship and they sink to the bottom. There are no cables and no joystick. The lander rests on the seafloor and films whatever approaches the light. When the timer expires or an acoustic release signal arrives, the release mechanism drops the weights and the vehicle floats to the surface on its own, often emerging miles from the ship’s expected position depending on deep currents. Recovery crews sometimes spend hours tracking a radio beacon before they can retrieve the unit.
Alan Jamieson, a marine ecologist who has led much of the hadal-depth research over the past two decades, designed the landers his teams used in the Pacific. His design philosophy prioritized simplicity and multiple layers of safety, because any failure at these depths cannot be repaired or rescued once the vehicle reaches the bottom. The advantage lies in that simplicity. No rope can break and no human life is at risk, so researchers can deploy several landers at once at different depths. That method helped break depth records.
In August 2022, the research ship DSSV Pressure Drop carried three high-resolution camera landers through three Japanese trenches over a two-month period as part of a decade-long study of the deepest fish on Earth. The project was built around systematic repeated surveys rather than a single dramatic attempt, and the researchers noted that finding such a rare animal at that depth generally requires dozens of deployments before one confirmed sighting is recorded.
The Japanese remotely operated vehicle Kaiko worked differently, tethered to a ship. It made hundreds of dives to hadal depths starting in 1995, becoming the second vehicle in history to reach the bottom of Challenger Deep after the Trieste, and continued collecting biological samples and video footage across dozens of expeditions over the next eight years.
The Woods Hole Oceanographic Institution built the hybrid vehicle Nereus in 2008. It could operate freely or be guided from the surface via an optical fiber cable the thickness of a human hair. The design combined the wide survey capability of a free robot with the precise real-time control of a tethered robot. Nereus reached Challenger Deep in 2009 and transmitted high-quality video through the glass thread, becoming the third vehicle in history to touch the bottom of that particular trench, after the Trieste in 1960 and Kaiko in 1995. Neither machine remains in service, and how each one ended reveals something about what that depth does to equipment.
Kaiko was lost at sea in 2003 when its communication cable snapped during a storm while operating in a different part of the Pacific, far from the Mariana Trench. It was a mechanical failure brought on by ordinary storm conditions rather than deep pressure.
Nereus ended differently. On May 10, 2014, it was seven hours into a planned nine-hour dive in the deepest part of the Kermadec Trench northeast of New Zealand. It had rested on the sediment at 9,990 meters for more than six hours. Then the team aboard the research vessel Thomas G. Thompson lost contact. Standard emergency recovery procedures failed. The crew searched near the dive site and spotted debris floating on the surface, later confirmed to be parts of Nereus. Scientists concluded that part of the vehicle had collapsed under pressure. It was the 30th day of a 40-day expedition, and Nereus was the only operating scientific vehicle at the time that could work at that depth. Before the expedition ended, it had already found previously unknown trench habitats and around a dozen species new to science, discoveries that remained valuable to researchers even after the vehicle responsible for finding them was gone.
The risk existed from the first landing. On January 23, 1960, as Jacques Piccard and Lieutenant Don Walsh approached the bottom in the Trieste, a sound like a gunshot rang out inside the cabin. One of the external viewing windows made of Plexiglas had cracked. The pressure pushed the remaining layers harder into the frame rather than shattering them inward, and the window held. The two men spent about 20 minutes on the seafloor and reported seeing living organisms there, surprising almost everyone, as prevailing scientific opinion at the time held that such extreme pressure would prevent any complex animal life from existing.
Sixty-five years of footage revealed that the most frequently observed object at that depth was not an animal but something discarded by a human: a plastic bag. At 10,898 meters, in 2017, the Japan Agency for Marine-Earth Science and Technology opened its deep-sea debris database to the public. The archive contained over 30 years of images and videos of waste collected by Japanese submarines and remotely operated vehicles, accumulated gradually across decades of separate research missions that were not related to pollution monitoring at the time they were recorded.
A team led by researcher Sanae Shiba examined the archive and published its findings in the journal Marine Policy in 2018. The team reviewed 5,010 dives and counted more than 3,000 human-made waste items, including metal, rubber, fabric, fishing gear, and plastic. About one-third of the classifiable debris was plastic. Of that plastic, 89% was single-use, the kind intended to be used once and discarded. The deepest item in the entire database was a plastic bag found at 10,898 meters in the Mariana Trench. The video was recorded in 1998 and sat in the archive for two decades, only reaching public attention when someone finally searched for it. It is a striking example of how evidence can remain unnoticed inside institutional files for years simply because no one asked the specific question that makes it relevant.
Below 6,000 meters, more than half of the debris the team recorded was plastic, and most of it was single-use. Deep-sea organisms appeared in 17% of the debris images, including sea anemones attached to bags and plastic tangled in cold seep communities, evidence that marine life was not only coexisting near the debris but in some cases growing directly on top of it. Many of the dives were more than 1,000 kilometers from the nearest land, ruling out any simple explanation involving nearby coastal waste drifting a short distance. The study was archival work done by people staring at old tapes on a screen. A year later, someone was at the bottom looking through a window with their own eyes.
On April 28, 2019, Victor Vescovo took the submarine Limiting Factor to the bottom of the Mariana Trench as the fourth leg of his Five Deeps Expedition, an attempt to reach the deepest point in each of the five oceans over a continuous mission lasting about 10 months. He spent around four hours there and reported seeing several creatures, some possibly new to science, along with a plastic bag and candy wrappers. The observation carries weight because so few people have had the opportunity to make it. By July 2022, 27 individuals had made documented visits to Challenger Deep across about 22 crewed descents. The submersible Sckuvo alone logged 15 of those trips between April 2019 and July 2022, roughly doubling the number of people who had visited that specific site within a few years. The list includes Kelly Walsh, son of Don Walsh from the 1960 dive, and Kathryn Sullivan, a former NASA astronaut who became the first person to visit both space and the ocean’s deepest point. For comparison, human spaceflight began in 1961, and by November 2021 the 600th person had left the planet. More than 20 times as many people have seen Earth from orbit as have sat on the bottom of Challenger Deep. The sample size for direct human observation is tiny, and trash was found in it twice.
The most common organism in Challenger Deep is Hirondellea gigas, a scavenging crustacean that consistently appears in baited traps on the bottom and survives by consuming whatever organic matter drifts down from above, including whale carcasses that support scavenger communities for years. Vertebrates have a much harder time. The deepest known one is the snailfish Pseudoliparis swirei, described in the Mariana Trench in 2017. It resembles a tadpole made of wet tissue paper. Chinese researchers who sequenced its genome found that its skull does not fully close, and a mutation appears to halt bone calcification early, leaving a thin skeleton that bends rather than shatters, an adaptation that helps the animal withstand pressure that would crush a fish with harder bones.
The camera record for any fish was set in August 2022 and announced in April 2023. Jamieson’s team, working with the University of Tokyo’s marine science and technology department, filmed a small snailfish at 8,336 meters in the Izu-Ogasawara Trench, breaking the previous record of 8,178 meters in the Mariana Trench. Days later, they caught two Pseudoliparis belyaevi snailfish at 8,022 meters in the Japan Trench, the first fish ever caught below 8,000 meters, which gave researchers physical samples instead of video footage alone. The fish measured between 20 and 25 centimeters long and fed on small crustaceans. Jamieson noted that the Izu-Ogasawara Trench is the warmest of the deep trenches, less than a degree warmer than the Mariana Trench, and that difference matters. He said that if anyone finds fish at greater depths, it will not be by a large margin.
No fish has been found in the deepest quarter of the ocean, roughly between 8,400 and 11,000 meters. For a long time, no one could explain why. In 2014, a team including Paul Yancey, Mackenzie Gerringer, Jeffrey Drazen, Ashley Rowden, and Jamieson published an answer in the Proceedings of the National Academy of Sciences. The key lies in trimethylamine N-oxide, or TMAO, a compound in a group known as piezolytes. Pressure tries to distort the shape of proteins at a molecular level, and TMAO stabilizes them, acting as a molecular scaffold that protects the protein’s three-dimensional structure from collapsing under the weight of water. Fish carry more of it the deeper they live, with levels rising from about 40 to 261 millimoles per kilogram between the surface and 4,850 meters. The problem is that TMAO also changes the animal’s internal salt concentration. Shallow-water fish operate at about 350 units of internal osmotic pressure compared to about 1,100 units for seawater. Adding enough TMAO brings those two ratios into balance, and then the fish’s internal fluid equilibrium works against it rather than protecting it. The team caught five snailfish from 7,000 meters in the Kermadec Trench, measured the highest TMAO levels ever recorded in a fish, and identified where the curves cross. The answer was about 8,200 meters. Below that depth, a fish would have to reverse its own water balance. Yancey noted a second limit. Too much TMAO makes proteins so stable that they stop working entirely. Myosin in muscles must move for muscles to contract, and enough TMAO would freeze them completely, meaning even if a fish solved the osmotic problem, it would eventually reach a point where its muscles could no longer contract. That creates a strict ceiling for vertebrates, and the snailfish filmed at 8,336 meters sits right at that boundary. Anything living deeper must be built on different rules, and in July 2025 a Chinese submarine showed what that looks like.
Between July 8 and August 17, 2024, the research vessel Tansuo Hao carried the submarine Fendouzhe, meaning “the striver,” through sections of the Kuril-Kamchatka Trench and the western Aleutian Trench in the northwest Pacific. The submarine had already reached Challenger Deep in 2020, carrying three Chinese scientists to 10,909 meters. During dive number 271, at 9,533 meters, the crew found dense clusters of tubeworms on black mud where the trench floor meets the base of the slope. Elsewhere they found expanses of clam-like bivalves buried in sediment so densely that one site was nicknamed “the clam bed.” The findings were published in Nature on July 30, 2025, by a large international team led by Shao Tong Bang and Muqin Du from the Institute of Deep-Sea Science and Engineering at the Chinese Academy of Sciences. The communities spanned about 2,500 kilometers at depths from 5,800 meters down to 9,533 meters, making them the deepest and most extensive chemosynthetic community known on Earth. Nothing there depends on sunlight. Fluids rich in hydrogen sulfide and methane move through faults that penetrate deep sediment layers, and isotope analysis indicated the methane is produced by microbes breaking down buried organic matter. Bacteria convert those chemicals into usable food, and many of the worms and clams host the bacteria inside their tissues, an arrangement biologists call chemosynthetic symbiosis. The idea had been proposed as a possibility for decades, but actual documentation was extremely rare, and the authors noted that given the geological similarity of other trenches, such communities may be far more common than anyone had assumed.
In February 2017, a team led by Jamieson published a study in Nature Ecology and Evolution that changed how researchers talk about deep ocean trenches. They used landers to collect amphipods, small shrimp-like predators, from depths between 7,000 and 10,250 meters in the Mariana and Kermadec Trenches. The two trenches lie about 7,000 kilometers apart on opposite sides of the Pacific, making it hard to dismiss the findings as a local anomaly. The researchers tested fat tissue for persistent organic pollutants. Two compounds stood out: polychlorinated biphenyls, used for decades as electrical insulation, and polybrominated diphenyl ethers, used as flame retardants. Regardless of depth, species, or trench, the animals were loaded with these pollutants. The highest PCB levels found in Mariana Trench crustaceans were 50 times higher than those in crabs from the Liaohe River system in China, one of the country’s most polluted river systems. PCBs were banned starting in the 1970s, with total global production between the 1930s and the ban reaching about 1.3 million tons. These substances do not naturally break down.
In February 2019, Jamieson and colleagues published a study in Royal Society Open Science examining the hindguts of 90 amphipods collected from six trenches around the Pacific rim, including Japan, Izu-Bonin, Mariana, Kermadec, New Hebrides, and Peru-Chile, at depths from 7,000 to 10,890 meters. Of the 90 animals, 65, more than 72%, had ingested at least one microplastic particle. In the Mariana Trench, the figure was 100%. Every animal examined from the deepest place on Earth contained at least one human-made fiber. Chemical analysis revealed a list resembling a clothing label: nylon, polyethylene, polyamide, polyvinyl alcohol, polyvinyl chloride, plus rayon and lyocell. Jamieson offered a comparison for what these fibers do to such a small animal, describing the human equivalent as swallowing a two-meter polypropylene rope and expecting no side effects.
While examining amphipods collected in November 2014 from the depths of the Serpentine, Johanna Weston, a doctoral student at Newcastle University, found microfibers in the hindgut of a specimen belonging to a species new to science. Analysis showed they matched roughly 84% of a material called polyethylene terephthalate, the plastic used in beverage bottles. The team named the species Eurythenes plasticus and described it in the journal Zootaxa on March 5, 2020, specifically to illustrate that a completely new species from an unexplored habitat had already been contaminated before humans even knew it existed.
Nuclear weapons testing in the late 1950s and early 1960s nearly doubled the amount of carbon-14 in the atmosphere, an increase researchers call “bomb carbon.” In 2019, a team led by geochemist Ning Wang of the Chinese Academy of Sciences published a study in Geophysical Research Letters using that signal as a tracer. They collected crustaceans from the Mariana, Mussau, and New Britain Trenches at depths down to 11 kilometers. Muscle tissue showed carbon-14 levels well above the organic matter suspended in the surrounding deep water, instead matching organic material collected from the surface of the Pacific. The conclusion was that these animals feed on debris falling from the sunlit surface rather than living on local material, meaning the surface and the trench floor are connected far more directly than anyone had assumed. The study also found that trench crustaceans grow larger and live longer than their shallow-water relatives, giving pollutants more time to accumulate inside a single animal over its lifetime.
Human activity releases more than 2,000 metric tons of mercury into the atmosphere every year. In November 2020, a team led by Joel Blum at the University of Michigan published research in the Proceedings of the National Academy of Sciences showing that mercury isotope ratios in snailfish and crustaceans in the Mariana and Kermadec Trenches matched mercury found in fish feeding at around 500 meters deep in the central Pacific, waters dominated by mercury from human sources. Blum summarized simply: “The mercury that was once in the stratosphere is now in the deepest trench on Earth.” A second team, led by Ruo Sun at Tianjin University, reached a compatible conclusion using landers in the Mariana and Japan Trenches.
On May 7, 2025, researchers from the Ocean Discovery League, led by Katie Croff Bell, published a study in Science Advances that compiled 43,681 submersible dive records going back to 1958 across waters of 120 countries. The team calculated that all those dives combined visually observed about 3,823 square kilometers of deep seafloor, less than 0.001% of the total deep seafloor worldwide. That is an area slightly larger than Rhode Island, or about one-tenth the size of Belgium. 65% of all observations came from the waters of just three countries: the United States, Japan, and New Zealand. The authors compared it to trying to understand all terrestrial wildlife from a land sample roughly the size of Houston. Bell’s point was not that nothing is known, but the opposite. Look at how much has been extracted from that tiny fraction, then ask how much remains. Mapping the shape of the seafloor with sonar is faster than visual observation, and even that lags behind full coverage.
On April 20, 2026, the Nippon Foundation and the GEBCO Seabed 2030 project announced that 28.7% of the world’s ocean floor has now been mapped to modern standards, about 104 million square kilometers, with nearly 5 million square kilometers added in a single year. When the project began in 2017, the figure was 6%.
Cameras have reached the deepest parts of the ocean since the 1990s, mostly on simple landers that descend, film, and float back to the surface. The deepest point, Challenger Deep, measures 10,935 meters or 35,876 feet according to the most accurate measurements available, not 38,000 feet. Only 27 people had documented visits there by July 2022. The machines have not always returned intact. Kaiko was lost in 2003, and Nereus collapsed under pressure at 9,990 meters in 2014. The most striking item in the footage was never a monster. It was a plastic bag filmed in 1998 at 10,898 meters, among more than 3,000 documented pieces of human debris, with levels of PCBs, microplastics, bomb carbon, and mercury already present inside the animals living there. There is also confirmed extraordinary life, such as the snailfish filmed exactly at the chemical limit researchers predicted for vertebrates in 2014, and a full chemosynthetic community of tubeworms and clams documented living off methane and hydrogen sulfide at depths down to 9,533 meters. Humans have visually observed less than 0.001% of the deep seafloor. The plastic bag arrived before the cameras did.
