Nearly 11 kilometres beneath the Pacific, crushing pressure, permanent darkness and scarce food create one of Earth’s harshest habitats, yet animals and microbes still survive there.
Brad Socha | September 5, 2026 | 7:52 PM EST
Featured image: The glass sponge Advhena magnifica observed during deep-sea exploration of the Marianas. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2016 Deepwater Exploration of the Marianas.
At the deepest known point in the ocean, there is no sunlight, the water is only a few degrees above freezing, and the pressure is more than a thousand times greater than at sea level. Yet the bottom is not lifeless.
The Challenger Deep, within the Mariana Trench in the western Pacific, reaches approximately 10,935 metres below sea level. If Mount Everest were placed there, its summit would remain more than two kilometres underwater.
These extreme trenches belong to the hadal zone, generally defined as ocean depths between 6,000 and 11,000 metres. Far from being empty, hadal environments contain specialized communities of amphipods, sea cucumbers, single-celled organisms and microbes. Fish survive at extraordinary depths as well, although evidence suggests even they reach a physiological limit before the deepest seafloor.
The result is an ecosystem unlike almost anything humans encounter at the surface.
Life Under Crushing Ocean Pressure
Pressure increases by roughly one atmosphere for every 10 metres of seawater. At the bottom of the Mariana Trench, organisms therefore experience pressures exceeding 1,000 atmospheres. There is no sunlight, temperatures are generally cold away from geothermal features, and food can be scarce.
Life has evolved ways to function under those conditions.
The Mariana Trench contains amphipods, shrimp-like crustaceans, including Hirondellea gigas, along with sea cucumbers and xenophyophores, unusually large single-celled organisms. NOAA documentation describes H. gigas feeding on plant and wood debris that has fallen from the surface world thousands of metres above.
Microbes extend the story to an even smaller scale. A 2026 review in Communications Earth & Environment found that microorganisms in hadal trenches possess adaptations that help cell membranes and proteins function under pressures of roughly 60 to 110 megapascals. These microbial communities also contribute to chemical and nutrient cycling in the trenches.
Fish present a particularly interesting limit.
In 2022, scientists filmed a snailfish at 8,336 metres in the Izu-Ogasawara Trench near Japan, establishing the deepest confirmed observation of a fish. Two snailfish were also collected from 8,022 metres in the neighbouring Japan Trench. The findings were published in 2023.
No fish has been confirmed anywhere near the approximately 10.9-kilometre bottom of Challenger Deep. Research indicates that the biological limit for fish may lie around 8,200 to 8,400 metres, partly because extreme pressure interferes with the molecular processes necessary for their bodies to function. Below that apparent boundary, known animal life consists of invertebrates rather than fish.
Food is another challenge. Much deep-ocean life ultimately depends on organic material produced near the surface and carried downward. Dead plankton, waste and other particles descend as what is commonly called marine snow. Larger carcasses and even wood can also deliver concentrated supplies of food to the seafloor.
But some deep-sea ecosystems operate differently.
Life Without Sunlight
Hydrothermal vents demonstrate that an ecosystem does not necessarily require direct energy from sunlight.
At these sites, seawater circulates through cracks in the ocean crust, becomes heated by geological processes and returns carrying dissolved chemicals. Microorganisms can use chemical reactions to produce organic matter through chemosynthesis, providing the foundation for communities that may include worms, mussels, shrimp and other animals.
The discovery of thriving hydrothermal-vent communities in 1977 fundamentally changed scientific understanding of where substantial ecosystems could exist. Instead of relying directly on photosynthesis, these communities can be powered by chemical energy originating from the interaction of seawater and the rocky Earth.
Hydrothermal vents should not, however, be confused with the deepest point of the Mariana Trench. Vents occur in numerous tectonically active regions of the seafloor, including parts of the broader Mariana region, but the organisms living at Challenger Deep face a different combination of extreme pressure, cold, darkness and limited food.
Scientists are still discovering how varied these habitats are.
The hadal zone consists primarily of isolated trenches and troughs. Those separations can effectively create deep-ocean islands, potentially allowing populations to evolve independently. NOAA describes hadal environments as among the most poorly explored habitats on Earth.
That makes claims about how many undiscovered deep-sea species remain impossible to quantify precisely. What scientists can say is that exploration continues to reveal organisms and ecological relationships that were previously unknown.
Exploring a World Humans Rarely See
Reaching these depths is itself an engineering challenge.
Scientists use remotely operated vehicles connected to research ships, autonomous underwater vehicles capable of following programmed missions, specialized landers and, more rarely, human-occupied submersibles. Cameras, sonar, sensors and sampling equipment allow researchers to map terrain, record animals and return biological or geological material to the surface.
Even the machines face the same physical problem as the organisms they study: extraordinary pressure. In 2014, the Woods Hole Oceanographic Institution’s robotic vehicle Nereus was lost at nearly 10,000 metres in the Kermadec Trench after operating in one of Earth’s most extreme environments.
Our picture of the seafloor itself remains incomplete. NOAA reported that only about 26% had been mapped to modern high-resolution standards as of June 2024. Mapping is not the same as directly observing an ecosystem, meaning the proportion explored visually and biologically in detail is smaller still.
The deepest ocean is therefore not an empty abyss. It is a collection of extreme habitats populated by organisms whose biology has been shaped by darkness, cold, pressure and isolation.
Nearly 11 kilometres below the surface, life persists. What else lives there, and how much remains undiscovered, is a question that continued exploration is only beginning to answer.
About the Author Brad Socha is the founder of The Universal Record, focused on sourced, factual global reporting. Coverage includes international news, geopolitics, technology, and major developments.
