The water pressure at the bottom of the Mariana Trench reaches roughly eight tons per square inch, and sunlight never reaches it. In 2018, researcher Shiba avoided the ocean entirely and searched video archives instead, reviewing 5,010 old dives that had received little attention. One scene from 1998 stopped her completely.

The trench was first discovered by the Royal Navy survey ship HMS Challenger on March 23, 1875, using a weighted rope. The rope kept running out, and the reading came back at 4,475 fathoms, about 8,184 meters, which the crew confirmed with a second survey in the same location. That single measurement was part of a broader four-year voyage around the world to collect oceanographic data systematically. The crew did not realize they had found the deepest place on the planet. They simply recorded the number and moved on, leaving it to later researchers to recognize its significance.

Every measurement since then has pushed the number deeper as instruments improved, from weighted rope to sonar pulses to satellite-corrected pressure sensors placed directly on the seafloor. In October 2010, the U.S. Navy survey ship USNS Sumner measured the bottom from the surface at 10,994 meters. The most accurate figure comes from June 2020, when Victor Vescovo conducted six transverse passes across the deepest basins in the submarine Limiting Factor, with three automated landers alongside, cross-checking multiple independent pressure readings taken directly at depth rather than relying only on sonar bounced from a distant ship above. The 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 appears online. That gap is not a rounding difference but a genuinely inflated number with no basis in any measurement.

Water pressure increases by about one atmosphere for every 10 meters descended. At the bottom of Challenger Deep, that means roughly 16,000 pounds per square inch, more than a thousand times what a person feels standing on the shore. Trieste, the first vessel to reach it in 1960, carried a steel sphere with walls five inches thick and room for two men in a space 38 inches across. It was a cramped, cold environment that the two men had to endure for the five hours the round trip took. Building something that survives there is difficult. Recovering it with usable video is another problem entirely.

The answer turned out to be surprisingly low-tech. Most footage of the deep ocean was not captured by a piloted submarine at all, but by landing vehicles. A lander is a frame carrying weights, floats, lights, a camera, and often a baited trap. It is dropped from the back of a ship and sinks to the bottom with no cables and no joystick. It settles on the seafloor and films anything that approaches the light. When the set time ends or a signal arrives, an acoustic release mechanism drops the anchor weights, and the vehicle floats back up on its own, often surfacing miles from the ship’s expected position due to deep currents. Recovery crews sometimes track a radio beacon for hours before retrieving the unit.

Alan Jamieson, a marine ecologist responsible for much of the hadal research over the past twenty years, designed the landers his teams used in the Pacific, prioritizing simplicity and multiple safety measures because any failure at those depths cannot be repaired or rescued once the vehicle reaches the bottom. The advantage lies in that simplicity. There is no rope to break and no human life at risk, so multiple landers can be dropped at once at different depths, which is how depth records were broken. In August 2022, the research vessel DSSV Pressure Drop carried three high-definition camera landers across three Japanese trenches over two months as part of a ten-year study of the deepest fish on Earth. The project was designed around systematic, repeated surveys rather than a single dramatic attempt, and the researchers noted that finding such a rare animal generally requires dozens of drops before one confirmed sighting.

The Japanese remotely operated vehicle Kaiko worked differently, tethered to a ship, conducting hundreds of dives into hadal depths starting in 1995. It became the second vehicle in history, after Trieste, to reach the bottom of Challenger Deep, and it continued collecting biological samples and video across dozens of expeditions over the following eight years. The Woods Hole Oceanographic Institution built Nereus in 2008, a hybrid vehicle that could operate freely or be guided from the surface via a fiber-optic 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 one. Nereus reached Challenger Deep in 2009 and transmitted high-quality video through that glass thread, becoming the third vehicle in history to touch the bottom of that specific trench, after Trieste in 1960 and Kaiko in 1995.

Neither machine remains in service, and how each ended says something about what that depth does to equipment. Kaiko was lost at sea in 2003 when its communication cable snapped during a storm while it was working in a completely different part of the Pacific, far from the Mariana Trench. It was a mechanical failure caused by ordinary storm conditions rather than deep pressure. Nereus ended differently. On May 10, 2014, Nereus was seven hours into a planned nine-hour dive in the deepest part of the Kermadec Trench northeast of New Zealand. It had settled on the sediment at 9,990 meters for more than six hours when the team aboard the research vessel Thomas G. Thompson lost contact. 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 reaching 16,000 pounds per square inch. It was the thirtieth day of a forty-day expedition, and Nereus was the only working scientific vehicle at the time capable of operating at that depth.

Timothy Shank, a Woods Hole biologist who helped create Nereus, said it allowed them to explore places they had not seen and ask questions they had not thought to ask before. Before that expedition ended, the vehicle had already found unknown trench habitats and about a dozen species new to science, discoveries that remained valuable 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 Trieste, a sound like a gunshot rang inside the cabin. One of the outer viewing windows made of Plexiglas had cracked. The pressure pushed the remaining layers tighter into the frame rather than shattering them inward, and the window held. They spent about twenty minutes on the seafloor and reported seeing living organisms there, which surprised nearly everyone because the prevailing scientific view at the time held that such extreme pressure would prevent any complex animal life entirely.

Sixty-five years of footage later, the most commonly seen and filmed object at that depth was not an animal but something a human had thrown away: a plastic bag. At 10,898 meters, and in 2017, the Japan Agency for Marine-Earth Science and Technology opened its deep-sea debris database to the public. The archive holds more than thirty years of images and video of waste collected by Japanese submarines and remotely operated vehicles, accumulated gradually over decades of separate research missions that had little to do with pollution monitoring at the time they were recorded. A team led by researcher Sanai Shiba examined the archive and published the results in the journal Marine Policy in 2018. The team reviewed 5,010 dives and counted more than 3,000 pieces of human-made waste, including metal, rubber, fabric, fishing gear, and plastic. About a third of the classifiable debris was plastic, and 89 percent of that plastic was single-use.

The deepest item in the entire database was a plastic bag found at 10,898 meters in the Mariana Trench. That video was recorded in 1998 and sat in the archive for two decades, only making headlines when someone finally went looking 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 would make it relevant. Below 6,000 meters, more than half of the debris the team recorded was plastic, and most of it was the single-use kind. Deep-sea creatures appeared in 17 percent of the debris images, including sea anemones attached to bags and plastic entangled in cold seep communities, evidence that marine life was not just living near this 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 out to sea. That 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 his 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 of all five oceans over a continuous mission lasting about ten months. He spent about four hours there and reported seeing several creatures, some possibly new to science, along with a plastic bag and candy wrappers. The reason that observation carries weight is how few people have had the opportunity to do it. By July 2022, 27 people had been documented reaching Challenger Deep across about 22 crewed dives. The submersible Sckafoo alone accounted for 15 of those trips between April 2019 and July 2022, nearly doubling the number of individual visitors to that specific site within a few years. The list includes Kelly Walsh, son of Don Walsh from the 1960 dive, and Kathy Sullivan, a former NASA astronaut who became the first person to visit both space and the deepest point in the ocean. For comparison, human spaceflight began in 1961, and by November 2021, the 600th person had left the planet. The number of people who have seen Earth from orbit is more than twenty times the number who have sat on the bottom of Challenger Deep. The direct human observation sample is tiny, and yet trash has been found in it twice.

The most common creature in Challenger Deep is Hirondellea gigas, a scavenging crustacean that consistently appears in baited traps on the bottom, feeding on whatever organic material drifts down from above, including whale carcasses that support scavenger communities for years. Vertebrates face a much harder time. The deepest known one is the snailfish Pseudoliparis swirei, described in the Mariana Trench in 2017. It looks like a tadpole made of wet tissue paper. Chinese researchers who sequenced its genome found that its skull does not close completely, and a mutation appears to stop bone calcification early, leaving a thin skeleton that bends rather than shatters, an adaptation that helps the animal withstand pressure that might crush a fish with more rigid 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 Pseudoliparis 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, giving researchers physical samples rather than only video footage. The fish measured between 20 and 25 centimeters 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 ever 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 of Whitman College, 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 member of a group of compounds known as piezolytes. Pressure tries to deform proteins at the molecular level, and TMAO stabilizes them, effectively acting as a molecular scaffold that protects the protein’s three-dimensional shape from collapsing under the weight of the water. Fish carry more of it the deeper they live, 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 salinity. Shallow-water fish operate at about 350 units of internal osmolarity compared to 1,100 for seawater. Add enough TMAO and those two ratios equalize, at which point the fish’s internal fluid balance 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 intersected. The answer was about 8,200 meters. Below that depth, a fish would have to reverse its own water balance. Yancey identified a second limit. Too much TMAO makes proteins so stable they stop working entirely. Myosin in muscles must move for muscles to contract, and enough TMAO would freeze them completely, meaning that even if a fish solved the osmotic problem, it would eventually reach a point where its muscles could no longer contract. That puts a strict ceiling on vertebrates, and the snailfish filmed at 8,336 meters sits right at that limit. 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, which means “striver,” across 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. On dive number 271, at 9,533 meters, the crew found dense clusters of tube worms over black mud where the trench floor meets the base of the slope. Elsewhere, they found expanses of clam-like bivalves buried in the sediment so densely that one site was nicknamed “the clam bed.” The results were published in Nature on July 30, 2025, by a large international team led by Shao Tong Pang and Mugen Du of the Institute of Deep-Sea Science and Engineering at the Chinese Academy of Sciences. These communities stretched across about 2,500 kilometers and ranged in depth from 5,800 meters down to 9,533 meters. They represent the deepest and largest chemosynthesis-based community known on Earth. Nothing there depends on sunlight. Fluids rich in hydrogen sulfide and methane move through faults that penetrate deep sediment layers, where 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. This had been proposed as a possibility for decades, but actual documentation was extremely rare, and the authors noted that given the geological similarities between other trenches, such communities may be far more common than anyone assumed.

In February 2017, a team led by Jamieson published a study in Nature Ecology & Evolution that changed how researchers discuss the deep ocean. They used landers to collect amphipods, small shrimp-like scavengers, from depths between 7,000 and 10,250 meters in the Mariana and Kermadec trenches. The two trenches sit about 7,000 kilometers apart on opposite sides of the Pacific, making it difficult to dismiss the results as a local coincidence. They tested the fatty tissue for persistent organic pollutants. Two types appeared strongly: PCBs, used for decades as electrical insulators, 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 amphipods were 50 times higher than those in crabs from the Liaohe River system in China, one of the most polluted river systems in the country. PCBs were banned starting in the 1970s, with global production between the 1930s and the ban totaling about 1.3 million tons. These substances do not break down naturally.

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: Japan, Izu-Bonin, Mariana, Kermadec, New Hebrides, and Peru-Chile, at depths between 7,000 and 10,890 meters. Sixty-five of the 90 animals, more than 72 percent, had ingested at least one microplastic particle. In the Mariana Trench, the figure was 100 percent. 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, PVC, plus rayon and lyocell. Jamieson offered a comparison for what these fibers do to an animal that small, 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 Suruga Bay, Joanna Weston, a doctoral student at Newcastle University, found microfibers in the hindgut of a specimen belonging to a species new to science. Analysis showed it matched roughly 84 percent with polyethylene terephthalate, the plastic used in drink bottles. The team named the species Eurythenes plasticus and described it in Zootaxa on March 5, 2020, specifically to illustrate that an entirely 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, collecting amphipods from the Mariana, Mussau, and New Britain trenches down to 11 kilometers. The muscle tissue showed carbon-14 levels significantly higher than the organic matter floating in the deep water around them, 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 closely than anyone assumed. The study also found that trench amphipods grow larger and live longer than their shallow-water relatives, giving pollutants more time to accumulate within 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 of the University of Michigan published research in PNAS showing that mercury isotope ratios in snailfish and amphipods from the Mariana and Kermadec trenches matched mercury found in fish feeding at about 500 meters deep in the central Pacific, waters dominated by mercury of human origin. Blum summarized it simply: mercury that was once in the stratosphere is now in the deepest trench on Earth. A second team, led by Ruo Sun of Tianjin University, reached a compatible conclusion using landers in the Mariana and Yap trenches.

On May 7, 2025, researchers from the Ocean Discovery League, led by Katie Croff Bell, published a study in Science Advances compiling 43,681 submersible dive records dating back to 1958 across the 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 percent of the total deep seafloor worldwide. That is an area slightly larger than Rhode Island, or about one-tenth the size of Belgium. Sixty-five percent of all observations came from the waters of just three countries: the United States, Japan, and New Zealand. The authors compared that to trying to understand all terrestrial wildlife from a sample the size of roughly the city of Houston. Bell’s point was not that nothing is known, but quite 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 observing it visually, and even that lags behind full coverage. On April 20, 2026, the Nippon Foundation and the GEBCO Seabed 2030 project announced that 28.7 percent 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, that figure was 6 percent.

The situation can be summarized plainly. Cameras have been reaching the deepest parts of the ocean since the 1990s, mostly on simple landers that sink to the bottom, film, and float back to the surface. The deepest point reached, Challenger Deep, stands at 10,935 meters or 35,876 feet according to the most accurate measurements available, not 38,000 feet. Only 27 people have been documented reaching it as of July 2022. Machines do not always return intact. Kaiko was lost in 2003, and Nereus failed under pressure at 9,990 meters in 2014. The unsettling part of the footage was never a monster but a plastic bag filmed in 1998 at 10,898 meters, alongside more than 3,000 documented pieces of human waste and levels of PCBs, microplastics, bomb carbon, and mercury already present inside the animals that live there. There is also extraordinary confirmed life, such as the snailfish filmed exactly at the chemical limit researchers predicted for vertebrates in 2014, and an entire chemosynthetic community of tube worms and clams documented living on methane and hydrogen sulfide down to 9,533 meters. Humans have visually observed less than 0.001 percent of the deep seafloor. The plastic bag got there before the cameras did.