Mariana Trench

Located in the Western Pacific, between Hawaii and the Philippines, near the small island of Guam, lies the Mariana Trench, the deepest part of the ocean, housing two of the planet’s lowest spots. This crescent-shaped trench is surrounded by unique environments such as vents emitting liquid sulfur and carbon dioxide, active mud volcanoes, and marine life adapted to extreme pressures.

Oceanic trenches are seafloor depressions formed by Earth’s plate tectonics. Over 50 major ocean trenches exist worldwide, with the deepest, including the Mariana Trench, found along the Ring of Fire, a circle of active volcanoes around the Pacific Ocean. These trenches mark convergent plate boundaries where two tectonic plates collide, pushing one beneath the other and creating deep chasms.

The Challenger Deep, at the Mariana Trench’s southern end, holds the title of the ocean’s deepest spot. Measuring its depth is challenging, but in 2010, the National Oceanic and Atmospheric Administration used sound pulses to determine a depth of 36,070 feet (10,994 meters), with other modern estimates varying slightly.

Discovered in 1875 by the British ship HMS Challenger, from which the Challenger Deep gets its name, the trench was revisited in 1951 by HMS Challenger II. These explorations, followed by subsequent measurements, revealed its impressive dimensions: approximately 1,500 miles (2,550 kilometers) long and 43 miles (69 kilometers) wide.

The Mariana Trench also hosts the ocean’s second-deepest point, the Sirena Deep. Located 124 miles (200 kilometers) east of the Challenger Deep, it plunges to a depth of 35,462 feet (10,809 meters).

For perspective, most ocean life exists above 660 feet (200 meters). Nuclear submarines typically navigate around 850 feet (260 meters) below the surface. Whales are rarely seen below 8,200 feet (2,600 meters). The Titanic rests at 12,467 feet (3,800 meters), and Mount Everest’s peak is 29,026 feet (8,848 meters) above sea level, making the deepest part of the Mariana Trench 7,044 feet (2,147 meters) deeper than Everest’s height.

The trench’s climate varies from active mud volcanoes and bubbling floor pockets releasing sulfur and carbon dioxide, to temperatures between 34°F and 39°F (1–4°C) at the bottom, with no light penetration and intense pressure over 1,071 times that at sea level. Yet, life thrives under these conditions.

Japanese oceanographers, sampling mud from the Challenger Deep, identified about 200 microorganism species, including microscopic plankton and shells. The trench’s inhabitants range from saucer-sized sponge-like xenophyophores to large shrimp-like amphipods and small sea cucumbers called holothurians. 

Remarkably larger species also inhabit the depths of the Mariana Trench, including the hadal snailfish. This small, pink, and completely scaleless fish dwells at nearly 27,000 feet (8,200 meters), making it the record-holder for the deepest fish ever captured on the seafloor. Its skin is so transparent that its liver is visible through it.

The first manned descent to the trench’s bottom was on January 23, 1960. Swiss engineer Jacques Piccard and US naval officer Don Walsh aboard the Trieste reached 35,814 feet (10,916 meters) in Challenger Deep. Over half a century later, in 2012, filmmaker James Cameron piloted the Deepsea Challenger to a depth just shy of this mark for National Geographic. In 2019, Victor Vescovo broke the depth record, reaching 35,853 feet (10,927 meters) in the DSV Limiting Factor.

Future explorations of the trench will likely use unmanned vehicles, though the quest to push the limits of human and technological exploration continues.