The deepest place on Earth is not a landmark most people will ever see, because it lies nearly seven miles beneath the surface of the western Pacific Ocean. The Mariana Trench is a crescent-shaped scar in the seafloor so profound that if Mount Everest were dropped into its deepest point, the mountain’s peak would still be submerged under more than a mile of water. That staggering scale, combined with crushing pressure and total darkness, makes the trench one of the least explored environments on the planet, harder to reach than the surface of the Moon.
Just how deep the trench really goes
The Mariana Trench stretches for roughly 1,500 miles across the seafloor near the U.S. territory of Guam and the Mariana Islands. Its deepest point, a slot known as the Challenger Deep, plunges to nearly 36,000 feet below sea level. According to NOAA Ocean Exploration, that is close to 11,000 meters straight down. By comparison, Mount Everest rises about 29,000 feet above sea level, which is why the famous claim holds up: place the tallest mountain on Earth at the bottom of the trench and its summit would remain thousands of feet underwater. The numbers are hard to grasp precisely because nothing in ordinary human experience operates on that vertical scale.
What carves a trench this deep
The trench is not a random gash but the product of plate tectonics. It sits at a subduction zone, where the massive Pacific tectonic plate slides beneath the smaller Mariana plate and bends downward into the Earth’s mantle. This slow, grinding collision pulls the seafloor into an extraordinarily deep V-shaped valley. As NOAA’s ocean researchers explain, subduction zones are also the birthplace of the region’s earthquakes and volcanic arcs, so the same forces that dug the trench also built the chain of islands beside it. Understanding these deep trenches, the focus of much of NOAA’s ocean exploration work, is central to understanding how the planet recycles its crust over millions of years.
A world of crushing pressure and darkness
Conditions at the bottom of the trench are almost unimaginably hostile. Sunlight cannot penetrate anywhere near that depth, so the Challenger Deep is locked in permanent blackness and hovers just above freezing. The weight of the water column overhead generates pressure roughly a thousand times greater than at the surface, equivalent to hundreds of times the pressure inside a car tire, enough to crush an ordinary submarine like a soda can. Building machines that can survive that environment is a formidable engineering challenge, and every dive requires vessels engineered to withstand forces that would instantly destroy standard equipment. That extreme is a large part of why the trench has been visited by people only a handful of times.
Life that thrives where nothing should
Despite the cold, dark and pressure, the trench is not lifeless. Scientists have found single-celled organisms called xenophyophores, swarms of shrimp-like amphipods, and ghostly snailfish living far deeper than many biologists once believed vertebrates could survive. These creatures endure without sunlight by feeding on the steady drizzle of organic debris that sinks from the sunlit waters far above, and on chemicals seeping from the seafloor. Their existence expands the known limits of life on Earth and offers clues about how organisms might survive in the hidden oceans thought to lie beneath the icy moons of the outer solar system. Each expedition to the trench tends to turn up species never seen before, a sign of how much remains undiscovered.
The few who have reached the bottom
Only a small number of people have ever descended to the Challenger Deep. The first crewed dive came in 1960, when a specially built vessel carried two explorers to the bottom in a journey that took hours to descend and lasted only briefly at the floor. It was more than half a century before a solo diver returned in a purpose-built submersible, and robotic and crewed expeditions since then have gradually added detail to the map of this remote realm. Even so, the deep ocean as a whole remains startlingly unexplored; as NOAA notes in its overview of how deep the sea can reach, a large majority of the seafloor has never been directly observed. The Mariana Trench, the deepest of all, stands as a reminder that some of the greatest frontiers left to explore are not in outer space but hidden beneath the waves of this planet.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
More from Morning Overview
