eleven kilometers below the surface of the Pacific Ocean lies the Mariana Trench, the deepest place on Earth and one of the most enigmatic. Its sheer inaccessibility has long fueled fascination and legends about what hides in the dark.
The trench was discovered by accident during the Challenger Expedition of 1875. A simple weight on a rope was used to measure depth in the Pacific. The device sank far beyond initial estimates, revealing depths of around 8,188 meters before more extensive measurements showed there was much more still to learn.
The trench takes its name from the nearby Mariana Islands, themselves named after Mariana of Austria, a queen consort of 17th-century Spain. The proximity gave the deepest feature on the planet its enduring title.
When exploration began in earnest, the oceanic abyss reminded many of Captain Nemo’s voyages in Jules Verne’s 20,000 Leagues Under the Sea. The era captured the imagination, but early technology could not unlock all of the trench’s mysteries, keeping its secrets mostly hidden for decades.
For any creature to survive at such depths, pressures can be thousands of times higher than at the surface. The darkness is absolute, and the temperatures hover just above freezing. Many attempts have been made, but only four manned expeditions reached the trench floor in history, each revealing astonishing life and geology.
1. Four manned expeditions reached the bottom
The first successful descent occurred on January 23, 1960. Jacques Piccard and U.S. Navy Lieutenant Don Walsh piloted a submersible named Trieste, designed by Piccard’s father, Auguste. The descent took five hours, and the pair spent about twenty minutes on the seabed before the ascent, which lasted three hours and fifteen minutes. They encountered an unknown ecosystem and the giant squid, Architeuthis, in an environment never before explored by humans.
Filmmaker James Cameron later repeated the feat. He descended alone to the trench floor in a submarine named Deepsea Challenger, gathering new data and samples. The dive exceeded ten thousand meters and took about eight hours, marking a landmark in modern deep-sea exploration.
The most recent notable expeditions occurred at the end of 2019 and the start of 2021. Victor Vescovo led the Limiting Factor mission, reaching depths around 10,900 meters. In 2021, the Chinese vessel Fendouzhe descended to roughly 10,909 meters with researchers who documented specimens and imagery to deepen understanding of life at extreme pressures.
2. The trench holds more depth than Everest
The deepest point sits near the southern end of a narrow valley that plunges to about 10,929 meters, with measurements sometimes placing the depth just over 11,000 meters. Even so—if Everest, the world’s tallest peak, stood underwater at its summit—the trench would still have about 2,000 meters of water above it.
3. Formed by subduction
The Mariana Trench was created when tectonic plates collide and one plate dives beneath another in a process called subduction. In this region, oceanic crust slips beneath other oceanic crust, producing a deep trench and often triggering volcanic activity that creates island arcs. Similar processes formed trenches such as the Japan Trench and the Puerto Rico Trench. When continents collide with oceanic plates, different but equally dramatic effects unfold, giving rise to mountain ranges and other features.
The trench’s formation is part of a broader pattern of Earth’s dynamic crust, where subduction zones are responsible for some of the planet’s most dramatic underwater features.
The region’s geology also shows how continental plates interact with oceanic crust, sometimes producing elevated ridges and deep seafloor basins in areas far from land. The Andes mountains, for example, owe their existence to a different style of plate interaction but illustrate the same powerful forces shaping Earth’s surface.
4. The Challenger Deep remains the lowest point
The deepest portion of the trench is the Challenger Deep, with depth estimates commonly cited between 10,902 and 10,929 meters. The name honors the HMS Challenger, a British Royal Navy ship that helped establish the trench’s discovery in 1875. The pressure there reaches roughly 1,095 times the surface pressure, a testament to the extreme conditions and the technical hurdles faced by explorers aiming to reach this spot. The Sirena Deep, at about 10,809 meters, stands as the second-deepest point within the same trench, located roughly 200 kilometers east of the Challenger Deep.
5. A cradle for life under pressure
The Marianas host a fragile, extraordinary ecosystem. At temperatures near freezing and in almost total darkness, creatures endure pressures that would crush most life forms. Yet a diverse array of organisms has adapted to these conditions. The trench supports plankton, glow-bearing fishes, and giant squid that seem lifted from science fiction. Deeper dives have revealed eels, sponges, and transparent fish, all thriving in the deepest, most hostile parts of the ocean. Jacques Piccard once described finding a “beautiful mud floor full of diatoms,” a reminder that life can flourish even where the sun never reaches. In 2011, xenophiophores were identified on the trench floor, organisms resembling sea sponges but consisting of complex, single-celled life forms. In 2018, the deepest dwelling fish ever documented, the Mariana snailfish (Pseudoliparis swirei), was found near 8,000 meters. Scientists estimate this tiny, translucent creature can withstand the weight of about 1,600 elephants above it.
The trench continues to reveal a world unlike any other on Earth, where life adapts to pressures and temperatures that would seem impossible to endure.
6. A National Monument
Much of the trench lies within the Mariana Trench Marine National Monument, a protected area in the Pacific. The region is home to some of the world’s oldest seabeds, dating back about 180 million years, a factor that helps explain the trench’s profound depth and enduring mystery.
7. Pollution reaches the extreme depths
In 2019, the Five Deeps expedition confronted the problem of human waste at the trench floor. Victor Vescovo reported discovering a plastic bag and candy wrappers even in such a remote location. The stark reminder emphasized the reach of pollution, no matter how deep one travels. The response highlighted a growing concern about protecting these pristine, vulnerable ecosystems from human impact.
The exploration teams continue to study the trench, assembling data on its life, geology, and possible future changes. It remains a powerful symbol of both Earth’s hidden depths and the ongoing effort to understand them more clearly.