Mariana Trench

The Mariana Trench is a massive, crescent-shaped oceanic trench located in the western Pacific Ocean. It sits east of the Mariana Islands and holds the title of the deepest oceanic trench on Earth.

This trench is part of a much larger geological system known as the Izu–Bonin–Mariana subduction system. This system marks the boundary where two massive tectonic plates meet and interact. Because of its extreme depth and unique environment, the trench is a vital area for scientific study. It helps researchers understand the movements of our planet's crust and the limits of life on Earth.

The formation of the trench is driven by a process called subduction. In this system, the western edge of the Pacific plate meets the smaller Mariana plate. The Pacific plate consists of some of the oldest oceanic crust on Earth, dating back up to 170 million years. Because this crust is so old, it is cooler and denser than the younger Mariana plate. This density causes the Pacific plate to be subducted, or thrust, beneath the Mariana plate.

As the plate sinks, it releases water that was trapped in its minerals. This water causes flux melting in the upper mantle. This melting process leads to the creation of earthquakes and volcanic island arcs, such as the Mariana Islands.

The topography of the trench includes several distinct features and depths. The deepest known point is located at the southern end of a small, slot-shaped valley called the Challenger Deep. The trench itself is shaped like a crescent and has specific measurements for length and width. Scientists have also identified other deep spots, such as the HMRG Deep, discovered by the Hawaii Mapping Research Group. Mapping efforts using sonar technology have even revealed four rocky outcrops that were likely once seamounts. These features show that the seafloor is complex and far from a simple, flat valley.

Humans have used many different methods to explore this deep environment throughout history. In 1875, the Challenger expedition first sounded the trench using a weighted rope. By 1951, the ship Challenger II used echo sounding, which is a more precise way to measure depth.

In 1960, Don Walsh and Jacques Piccard completed the first crewed descent using the bathyscaphe Trieste. They used iron shot for ballast and gasoline for buoyancy to manage their depth. More recently, in 2012, James Cameron reached the bottom in the Deepsea Challenger. In 2019, Victor Vescovo became the first person to dive into the Challenger Deep more than once using the DSV Limiting Factor.

The physical conditions at the bottom of the trench are extreme. At the maximum depth of approximately 11,000 metres, the water column exerts immense pressure. This pressure is about 1,071.8 times the standard atmospheric pressure at sea level, or eight tons per square inch. The temperature at these depths remains around 1 to 4 degrees Celsius.

These conditions make the trench one of the most difficult places on Earth for technology to operate. Even specialized equipment, like titanium-shelled hydrophones, must be designed specifically to withstand such massive weight.

Despite these harsh conditions, life thrives in the Mariana Trench. Researchers have discovered microbial life forms and single-celled organisms called monothalamea. Some of these monothalamea are surprisingly large, growing to more than 10 centimetres. In 2014, scientists filmed the Mariana snailfish at a depth of 8,000 metres, setting a record for the deepest fish seen on video. Some species also exhibit deep-sea gigantism, where they grow much larger than their relatives in shallower waters. These organisms, including large amphipods known as supergiants, show how life adapts to high pressure and darkness.

Human impact has reached even these remote depths through pollution. Scientists have found extremely high concentrations of PCBs, a banned chemical toxin, in crustacean scavengers. Furthermore, 100% of the amphipods studied contained at least one piece of microplastic in their stomachs. In 2019, explorers even found a plastic bag and candy wrappers at the bottom of the trench. Even carbon-14 from nuclear bomb testing has been detected in aquatic animals there. These findings connect the deep ocean to the environmental changes happening on the surface of our planet.