7 Strange Discoveries About the Mariana Trench

The Mariana Trench is located in the western Pacific Ocean, east of the Philippines, and south of Japan. This oceanic trench is the deepest on Earth, forming a crescent-shaped ‘scar’ in the sea. The trench was formed by tectonic plate subduction where the Pacific Plate moves under the Philippine Plate, and its deepest point is known as Challenger Deep. Challenger Deep plunges nearly seven miles, deeper than Mount Everest is tall. Despite the crushing depth and complete darkness, the trench hosts several life forms, including snailfish and goblin sharks.

The Mariana Trench is renowned for its extremes and the challenges it presents to adventurers and explorers. Only a handful of human descents have ever been completed, and each mission is not only risky, but extremely technical and very expensive. Still, for all its fame, there is a lot of mystery surrounding this part of the ocean. Scientists have only explored a fraction of it, yet they have already uncovered unsettling findings, from plastic bags sitting at the very bottom to bizarre deep-sea creatures with see-through heads and gigantic bug-like bodies. Each new dive seems to reveal something unexpected, along with some strange discoveries.

A Grocery-Store Plastic Bag Sitting at the Very Bottom of Earth’s Deepest Pit

Plastic is one of the worst and most harmful scourges of modern life. It is so bad that plastic has even reached the deepest parts of the ocean. In 2019, American explorer Victor Vescovo descended into the Mariana Trench in an attempt to break the record for the deepest dive ever made. He spent four hours at the bottom of the trench in a submersible, where he found various sea creatures floating in the dark waters. He also found sweet wrappers and a grocery-store plastic bag right at the bottom.

This shocking discovery was made in a location where water pressure exceeds 1,000 times that at sea level. It is a hostile environment where temperatures hover just above freezing, and it is always pitch-dark. Most deep-sea creatures give the trench a wide berth, yet human pollution has reached it. Scientists believe plastic sinks very slowly to such depths, or is carried there by strong ocean currents. Once plastic settles on the ocean floor or in a trench, it can remain there for centuries due to the absence of sunlight and low oxygen levels. There is also too little biological activity for the plastic to break down. Most disturbing of all, the Mariana Trench, once believed to be completely isolated from humans on Earth’s surface, is now part of their environmental footprint.

See-Through Fish and Giant Bug-Like Creatures Surviving Under Crushing Black Water

While the discovery of plastic bags is unsettling, the discoveries of some Mariana Trench animals are truly strange. The Dumbo octopus is the ‘cutest’ of the bunch, but also one of the most vicious creatures down there. These octopuses swallow their prey alive and whole. Then there is the barreleye fish with its see-through head. The head has two barrel-shaped eyes that look mostly upwards, so the fish can see the shadows or silhouettes of its preferred prey in the crushing darkness. Scientists did not even know that the barreleye fish existed until 1939, when one was pulled from 2,500 feet below the surface. Even now, so many years later, scientists still know little about the life cycle and reproductive patterns of this weird fish.

The trench is also home to giant amphipods and giant isopods, which represent a phenomenon known as deep-sea gigantism. Amphipods are crustaceans related to shrimp. When they live near the surface, they stay small, often growing to just a few centimeters. However, when found in the trench, some exceed 30 centimeters. These giant bug-like creatures look like oversized, armored insects as they crawl and swim through the darkness. Their size is puzzling, given how scarce food is at these depths. And their ability to withstand crushing pressure is also strange. Their cells, proteins, and membranes are built to resist being squeezed flat, but experts do not really know how or why this works.

Hydrothermal Vents Spewing Superheated Water and Minerals

One of the most dramatic discoveries in the Mariana Trench is that some parts of it are not cold, dark, and still. Some sections are almost violently active, with hydrothermal vents cracking open the sea floor and releasing water heated deep within the Earth. This water can reach temperatures above 400 degrees Celsius and burst out, carrying dissolved metals and chemicals toxic to most life. Still, sea life gathers around these vents.

In fact, there are entire communities around them, feeding on chemistry instead of sunlight. Bacteria convert sulfur and other minerals into energy. Larger animals depend on these bacteria, either ingesting them or harboring them within their bodies. Some of the creatures that cluster around the vents include tube worms and clams. They form dense colonies in an otherwise empty landscape, creating a scene resembling an underwater industrial zone, with plumes of dark mineral ‘smoke’ rising into the water. This discovery proved to scientists that life does not need sunlight to exist, and that energy can emanate from the Earth itself. This realization changed not only how scientists think about life on the blue planet but also about life elsewhere in the vast universe.

Bomb Carbon from Nuclear Tests Found in Deep Sea Creatures

Just like the Mariana Trench has not escaped humans, neither have the creatures that inhabit the deep. In 2019, scientists announced that they had found radioactive carbon-14 in the flesh of crustaceans in the trench. The carbon levels detected were high enough for the group of experts to believe that it originated from a nuclear bomb detonation. The first aboveground nuclear detonations were conducted in 1945. Scientists can determine the extent to which the resulting radioactive isotopes spread by measuring carbon-14 levels. Carbon-14 is produced by nuclear reaction when neutrons collide with nitrogen atoms in the atmosphere. When hydrogen bombs were tested during the 1950s and 1960s, carbon-14 levels in the atmosphere almost doubled. Over time, an insignificant amount of the carbon decayed. But the rest spread worldwide, being ingested by plants, animals, and humans.

Before the discovery in 2019, scientists did not know whether so-called bomb carbon had reached the deepest parts of the ocean. Then they trapped and tested the aforementioned crustaceans and found high levels of carbon in their tissues and guts. These levels were much higher than those present in the surrounding water. The team concluded that the isotopes reached the trench via the natural food chain. The carcasses and fecal matter of surface animals fall through the water column. The crustaceans would feed on this and then absorb what is left of the nuclear signature.

Animals in the Trench Contain Mercury at Unexpectedly High Levels

The animals in the trench simply cannot catch a break. In 2020, researchers discovered that human activities are also causing toxic mercury pollution to reach the most inaccessible parts of the ocean, including the Mariana Trench. It is also the sinking carcasses of fish and other animals that deliver this pollution via the water column. Most of that mercury started as emissions from coal-fired power plants, incinerators, and mining operations. This means that the mercury that was once in the stratosphere is now affecting marine life in the trench.

In the U.S. and Europe, mercury emissions have declined over the past few years. But in China and India, coal use is expanding, and global mercury emissions continue to rise. Researchers continue to study the mercury cycle in the world’s oceans to understand how it will affect fish caught in shallower waters and, by extension, the seafood people eat.

A Bizarre Species of Jellyfish Captured on Camera

Fortunately, not all the discoveries in the trench are devastating to deep-sea animal life. Some of them are both bizarre and very exciting. In 2016, U.S. researchers were trawling the trench and captured something on camera that they had never seen before. They were taking pictures in the Enigma Seamount at a depth of around 3,700 meters when a weird-looking jellyfish came into view. The jellyfish was colorful with thin, outstretched tentacles and an inactive bell. The team observed that the creature was not chasing its prey, but instead, it was suspended in the deep, waiting for unsuspecting organisms to approach it.

While they recorded the jellyfish, its internal parts and body appeared to glow, leading the team to believe that it was part of the genus Crossota. Some, however, were of the opinion that they had discovered an entirely new species of jellyfish. The biggest question that remains is what else could be floating around the trench that scientists have never seen before?

Silent Mud Volcanoes That Erupt Without Fire

In the wider region of the Mariana Trench, scientists have made a discovery that has nothing to do with strange sea creatures or pollution. What they found were underwater mud volcanoes that do not explode or glow, but instead, ooze cold mud, fluids, and gases from deep below the seafloor. The mud originates from sediments buried beneath the ocean floor, which are compressed by immense pressure when tectonic plates collide. The pressure forces the mud and fluids through cracks in the crust, forming dome-shaped, low-lying volcano structures on the seabed. Some of them rise hundreds of meters above the surrounding sea floor.

In 2025, scientists exhumed blue goo from some of these volcanoes at a depth of nearly 3,000 meters. They found fats from living organisms in the samples, despite the goo having a pH of 12, which can cause severe burns to human skin. The fats were derived from bacterial and archaeal cell membranes. These particular microbes produce energy from methane by consuming sulfate. This process creates hydrogen sulfide. Before the discovery, scientists only presumed the presence of methane-producing microorganisms in the trench systems. However, the blue goo findings directly confirmed it.

The Deepest Place On Earth Still Holds Many Secrets

The Mariana Trench proves that no place on Earth is untouched, whether by human activities or other processes. At its most profound depths, scientists continue to discover astonishing life and signs of human impact. These discoveries continue to surprise and horrify the world with the extent to which pollution can travel and the remarkable ways animals adapt to the dark, crushing depths. Today, much of the trench remains unexplored, so each new dive brings answers, only to raise more questions. What everyone can take away from the trench right now is that the planet needs more protection than ever before, to prevent further consequences in places previously believed to be unspoiled.