The deepest point on Earth, located roughly seven miles down in the Mariana Trench, has been reached by only a small number of people since the first attempt in 1960. That initial descent nearly ended in failure, and the risks and costs involved kept government agencies away from the site for decades. It was only through privately funded missions that researchers returned, eventually collecting samples that have since raised unresolved questions about the nature of life at extreme depths.
On January 23, 1960, Swiss explorer Jacques Piccard and U.S. Navy Lieutenant Don Walsh climbed into the Trieste, a steel submersible, and descended into Challenger Deep, the lowest point in the trench. The journey took nearly five hours. About 30,000 feet into the descent, the outer window cracked and the vessel shook, but turning back at that depth was not practical, so the pair continued. They reached the ocean floor at a depth of 10,911 meters, where pressure was high enough to collapse most structures. They stayed for 20 minutes before beginning their return, prompted by the damaged window.
Both men reported seeing a flatfish resting on the seafloor. That detail has been debated for decades, as scientists had not expected any animal to survive under such pressure. The dive demonstrated that humans could reach the deepest point on Earth, but it also showed how easily such a mission could become catastrophic. A cracked window at that depth does not mean a small leak; it can result in immediate structural failure. The two men returned safely, but the trip made clear that any repeat attempt carried serious risk.
Following that 1960 dive, nobody returned to Challenger Deep for 52 years. The gap was not due to a lack of interest but rather a combination of cost, risk, and timing. Building a vehicle capable of surviving the immense pressure at that depth is a major engineering challenge. The Trieste was retired not long after its historic dive, and developing a replacement would have cost tens of millions of dollars with no guarantee of success.
At the same time, the United States was directing its scientific budget and public attention toward the space race. The moon landing offered clear goals and national pride, while deep ocean exploration was expensive, largely invisible to the public, and carried no possibility of rescue if something failed. Government funding for crewed deep trench missions dried up. Robotic submersibles improved over the following decades and were used to explore shallower regions, but the deepest point on Earth remained largely unexamined by direct human observation. It was not abandoned because scientists had stopped caring; it was abandoned because the cost and risk outweighed the benefits without a safety net.
In March 2012, filmmaker and explorer James Cameron piloted a submersible called the Deepsea Challenger solo to the bottom of Challenger Deep. He spent nearly three hours on the seafloor, longer than anyone before him. The vehicle was built and funded largely through his own resources because government agencies were not willing to support another attempt. Cameron brought back high-definition video and physical samples from a location that had barely been documented in half a century. His team also confirmed that the vehicle had suffered hydraulic fluid leaks during the descent, a reminder that the pressure at that depth still finds weaknesses in equipment despite decades of engineering progress. After that single trip, the Deepsea Challenger was largely retired from further deep dives. The mission succeeded, but maintaining a vehicle rated for that kind of pressure remained expensive and dangerous.
In 2019, businessman and explorer Victor Vescovo led the Five Deeps expedition, a privately funded program aimed at reaching the deepest point in each of the world’s five oceans. His submersible, the Limiting Factor, descended into Challenger Deep multiple times in a single year, more than all previous human visits combined. Researchers working with the expedition collected water and sediment samples from depths below 10,400 meters. When scientists analyzed the genetic material and published their findings in the journal Microbiome, they found bacteria that specialize in breaking down hydrocarbons at concentrations higher than any previously recorded, including at oil spill sites. The researchers described the result as unexpected, and the paper used the word “shocking.”
No clear explanation emerged for the presence of that much organic material at a depth with no sunlight or obvious source of oil. Some of the material may have sunk from the surface, but sediment samples also contained naturally occurring hydrocarbons that appeared to come from within the trench itself. That finding raised questions about what else might be living at extreme depths.
The trench continued to test the limits of equipment. During a separate research expedition, a lander built to withstand extreme pressure imploded before it could return any data. The vehicle was lost in seconds. That kind of failure is common enough that scientists plan for it. Over the full length of the Mariana Trench, which spans roughly 2,550 kilometers, the number of missions that have produced usable data from its deepest sections can still be counted in the dozens after more than 60 years of exploration. The environment punishes even small mistakes without warning, and there is no chance of rescue once something fails thousands of meters underwater.
A separate line of research has raised further questions about oxygen production in the deep ocean. For more than a century, biology taught that oxygen comes from photosynthesis, which requires sunlight. Roughly half of every breath a person takes comes from phytoplankton near the ocean surface, and the rest comes from plants on land. Without light, there should be no new oxygen being made.
Professor Andrew Sweetman at the Scottish Association for Marine Science first noticed something unusual in his measurements in 2013. He was running experiments on the abyssal seafloor of the Pacific Ocean in the Clarion-Clipperton Zone, roughly 4,000 meters down. He placed sealed chambers on the seafloor and tracked oxygen levels inside them over time. In a place with no sunlight and no plants, oxygen should slowly disappear as organisms inside the chamber consume it. Instead, the readings rose, climbing to more than three times the surrounding background level over two days.
Sweetman initially assumed it was an instrument error. He had the equipment recalibrated and ran the test again, and the oxygen kept rising. He spent close to a decade repeating the experiment and having other researchers check his methods before publishing the results in Nature Geoscience in 2024. The likely source turned out to be small, potato-sized rocks called polymetallic nodules, which are rich in metals such as manganese, cobalt, and nickel and are scattered across wide stretches of the deep Pacific floor. These nodules carry a measurable electric charge on their surface, with voltages recorded up to nearly one volt on a single rock, about two-thirds of the output of a standard AA battery. Sweetman’s team proposed that this natural charge might be strong enough to split seawater into hydrogen and oxygen through a purely chemical and geological process, something that had not been documented on the seafloor before.
That finding has been disputed by other researchers who question whether electrolysis from the nodules is the correct explanation or whether something else affected the readings. Nature Geoscience posted an editor’s note in 2026 stating that parts of the original paper were under continued review. The debate remains active and unresolved. What has not been explained away is the set of readings themselves, a decade of repeated measurements that no one has fully accounted for using the assumption that oxygen only comes from sunlight.
The deep ocean has also drawn attention from space agencies. Jupiter’s moon Europa and Saturn’s moon Enceladus both have liquid oceans hidden beneath thick shells of ice, with no sunlight reaching them. Enceladus has been observed venting water vapor through cracks in its icy surface, indicating that its hidden ocean is interacting with the rocky material beneath it. Scientists believe both moons may have hydrothermal activity on their seafloors, with hot water mixing with rock in total darkness, similar to vent systems found in Earth’s oceans.
To prepare for future missions to these moons, NASA needed to understand how life or chemical energy might form in the darkest ocean environments available to study on Earth. A NASA program called SUBSEA, built in partnership with NOAA and the Ocean Exploration Trust, sent researchers to study underwater volcanoes and vent systems whose pressure, temperature, and chemistry most closely match predictions for Enceladus. The logic was that if scientists want to know what instruments should search for on an ocean moon, the best approach is to study the most extreme ocean environment available on Earth first and build detection strategies around what turns up. The bacteria at Challenger Deep and the rising oxygen levels in the Pacific are thus not just local discoveries; they may inform what future spacecraft look for on completely different worlds.
In summary, the first dive in 1960 nearly ended in disaster and discouraged quick follow-up. Fifty-two years of limited activity followed, driven by cost, risk, and national focus on space. A private filmmaker broke that silence in 2012, and a private expedition in 2019 collected biological data that reignited scientific interest. The oxygen readings from the wider Pacific floor have challenged long-standing assumptions about where oxygen comes from. The findings have been published in peer-reviewed journals, though some remain under review. The connection between Earth’s deep ocean and the icy moons of Jupiter and Saturn is documented in NASA’s published research.
Fewer than a handful of crewed missions have ever reached the bottom of the Mariana Trench. The reasons for the long gaps were never about losing interest; they were about cost, risk, and timing. What little has been found down there has been unusual enough to keep scientists, and now a space agency, looking back down instead of only looking up.
