Ten kilometres under the Pacific, beyond light, colour and ordinary intuition, something quietly thriving has forced scientists to rethink life itself.
In a trench so deep it crushes steel and erases sunlight, a Chinese research team has stumbled upon a thriving community of strange organisms, living off chemical reactions in the seabed rather than the Sun. Their work in the Kuril trench, north of Japan, now challenges what we thought we knew about how — and where — life can exist on Earth.
A hidden landscape where light never reaches
Below 6,000 metres, the ocean slips into what specialists call the hadal zone. Here, there is no natural light, temperatures hover just above freezing, and pressure exceeds a thousand times that at sea level. For decades, many researchers suspected only scattered microbes and a few hardy scavengers could cope with such brutal conditions.
The Kuril trench, which stretches between Russia’s Kamchatka Peninsula and Japan’s northern islands, plunges to more than 10,000 metres. In 2024, the crewed Chinese submersible Fendouzhe carried a scientific team, led by researcher Xiaotong Peng, into this black chasm between the Kuril and Aleutian island chains.
Far below 9,500 metres, their cameras and sampling arms revealed something unexpected: dense patches of tubeworms rising from dark sediments like ghostly thickets. Around these pillars of soft tissue, crustaceans and clams clustered together, forming a bustling, if alien, neighbourhood on the trench floor.
Instead of a lifeless abyss, the Kuril trench hosts what may be among the deepest functioning ecosystems ever recorded on our planet.
Analyses published in the journal Nature in 2025 suggest that similar habitats could stretch for more than 2,500 kilometres along the seafloor. Rather than isolated oases, these sites may link up into a loose biological corridor, a kind of hidden hadal highway where chemistry fuels life in near-total darkness.
The Kuril trench: a scar in the crust, pulsing with chemistry
Geologically, the Kuril trench is a product of subduction: the Pacific tectonic plate slides beneath the smaller Okhotsk plate at a rate of several centimetres per year. That slow collision carves a deep groove in the seafloor and fractures the crust, allowing fluids from inside Earth’s outer layers to leak upwards.
Working from the research vessel Tan Suo Yi Hao, Peng’s team combined video surveys, sediment cores and water samples to piece together what drives this hadal ecosystem. They homed in on seabed seep sites where cold fluids, rich in methane and hydrogen sulfide, ooze out of the mud.
Laboratory measurements revealed high concentrations of methane generated not by geological processes alone, but by microorganisms. These microbes take carbon dioxide buried in the sediment and convert it into methane, releasing energy that can be harnessed by other bacteria.
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The entire food web rests on chemical energy released when microbes process methane and sulfur compounds in the crust.
These so-called chemosynthetic bacteria act like plants without sunlight. They fix carbon and build organic matter using chemical reactions instead of photosynthesis. Tubeworms known as siboglinids host these microbes inside their own tissues, effectively outsourcing digestion to an internal chemical factory.
Nearby, giant clams, small shrimp-like amphipods and sea cucumbers (holothurians) feed on microbial films, dead worms and organic particles drifting down from above. Each group is tuned to crushing pressure, low oxygen, and the toxic mix of gases seeping from the seabed.
Life at the limit: what survives at 10,000 metres
The hadal residents spotted in the Kuril trench are not generic deep-sea organisms simply pushed a bit deeper. They show distinct anatomical and physiological tweaks that let them function where most species fail.
- Siboglinid tubeworms: lack a normal gut; instead, they host symbiotic bacteria in a special organ called a trophosome.
- Bivalves (clams and mussels): use their gills both for breathing and for housing chemosynthetic microbes.
- Amphipods: have flexible shells and pressure-tolerant enzymes that keep their cells working under immense compression.
- Holothurians: sift through sediment, recycling organic debris and redistributing nutrients across the trench floor.
Their membranes, proteins and cell structures are subtly altered to prevent collapse or malfunction at pressures that would shred most shallow-water life. Many hadal animals also show slow growth, delayed reproduction and long lifespans, a strategy that fits a cold, energy-limited habitat.
How chemistry replaces sunlight
On land and in surface waters, most food chains rest on photosynthesis. Sunlight powers the formation of sugars in plants and algae, and everything else depends on that starting point. In the Kuril trench, the starting point is different.
Here, life runs on chemosynthesis — converting chemical energy from methane and sulfur into organic matter, without any help from the Sun.
At seep sites, methane and hydrogen sulfide rise from the seabed and diffuse into the surrounding water. Bacteria grab these compounds and use them as fuel for chemical reactions that build complex carbon molecules. Oxygen or nitrate in the water serves as the other reactant, completing the process.
From there, the logic resembles familiar ecosystems. Primary producers — the chemosynthetic microbes — feed worms and clams. Those, in turn, feed opportunistic scavengers and predators. Microbes also drive crucial recycling, breaking down waste and dead tissue so nutrients remain available.
Rethinking the limits of life on Earth and beyond
The existence of such a robust system at these depths challenges the old picture of the deep ocean as a biological desert. Instead, trenches may act as hotspots of chemical and biological activity, tightly coupled to shifting geological forces below.
Astrobiologists are paying attention, too. Many scenarios for life on other worlds have leaned on something like this: dark oceans, rocky interfaces, and chemical gradients that microbes can exploit. The Kuril trench offers a real-world test case for that idea.
| Environment | Main energy source | Potential analogue |
|---|---|---|
| Kuril trench seeps (Earth) | Chemical reactions involving methane and sulfur | Early Earth seafloor, deep subsurface habitats |
| Subsurface oceans on Europa (Jupiter’s moon) | Rock–water interactions, tidal heating | Hadal trenches with active fluid circulation |
| Martian underground brines | Potential chemical gradients in salty water | Microbial communities in cold, high-pressure sediments |
If chemistry can sustain intricate communities at 10,000 metres, similar systems might emerge wherever liquid water, rock, and a steady source of energy coexist, even in the absence of sunlight.
A fragile frontier facing human pressure
While these findings fascinate planetary scientists, they also raise uncomfortable questions for policymakers. Several nations and private companies are weighing industrial-scale mining of the deep seabed for cobalt, nickel, rare earths and other metals critical for batteries and electronics.
Much of the attention has focused on abyssal plains at depths around 4,000 to 5,000 metres, where metal-rich nodules coat the seafloor. Yet the Kuril trench work shows that even deeper, seemingly barren regions can host complex, slow-growing ecosystems that depend on subtle chemical and geological balances.
Disturbing sediments, altering fluid flows or changing pressure gradients could disrupt habitats we barely understand, in places almost impossible to restore.
Because organisms in the hadal zone often grow and reproduce slowly, they may struggle to recover from sudden physical damage or long-term pollution. Noise from heavy machinery, sediment plumes, or the loss of seep sites could ripple through food webs that took millennia to assemble.
Key concepts behind this abyssal ecosystem
Several scientific ideas sit at the heart of the Kuril trench findings and help explain why they matter well beyond oceanography.
Chemotrophy and chemosynthesis
Chemotrophy refers to life forms that gain energy from chemical reactions, rather than from light. Chemosynthesis is the process where organisms use that chemical energy to build organic molecules from simple ingredients such as carbon dioxide. At Kuril seep sites, bacteria oxidise methane or hydrogen sulfide and use the released energy to form biomass.
This pathway allows life to function in any place where a chemical gradient exists — for example, where reduced compounds from the crust meet more oxidised seawater. Chemosynthesis underpins not just trench ecosystems, but also hydrothermal vents, some cave systems and deep subsurface microbial communities within rocks.
Subduction zones and life
Subduction zones, like the one forming the Kuril trench, are usually framed in terms of earthquakes, tsunamis and volcanoes. Yet they also create temperature and pressure conditions that drive fluid circulation through the crust.
As seawater penetrates fractured rocks and reacts with minerals, it picks up gases and nutrients, then rises back towards the seafloor. Around seeps, that returning fluid sets the stage for chemosynthetic life. In a sense, plate tectonics doubles as a planetary life-support system, generating the chemical imbalances that microbes can exploit.
What this hadal research can teach us next
Scientists are now planning follow-up missions to map how widespread these seep-based communities are, and how quickly they respond to natural shifts in tectonic activity. Autonomous landers and new long-duration moorings could monitor changes in methane release, fluid chemistry and animal populations over years rather than days.
There is also growing interest in how adaptations seen in hadal species — pressure-resistant enzymes, flexible membranes, unusual symbioses — might support medical or industrial innovations. For example, pressure-stable proteins could improve certain chemical processes, while microbial pathways might point to new ways of capturing carbon or breaking down pollutants.
For anyone watching policy debates on deep-sea mining, the Kuril trench serves as a reminder that the ocean floor is not a blank slate of mud and metal. It is a patchwork of unknown habitats, some of them reliant on geological processes that operate over millions of years, all linked into the broader climate and carbon systems that shape life at the surface.