Mariana Trench is an underwater depression located about 120 miles (200 kilometers) east of the Mariana Islands in the Pacific Ocean. The trench is about 1,580 miles (2,550 kilometers) long but has an average width of only about 43 miles (69 kilometers). The trench is part of the Ring of Fire, a zone along the edges of the Pacific Ocean that has many volcanoes and earthquakes. The deepest part of the Mariana Trench, called the Challenger Deep, is located near the trench’s southern tip. There, the ocean floor is about 36,070 feet (10,994 meters) below the ocean surface. It is the deepest known spot in the world.
The Mariana Trench was formed by the slow movement of tectonic plates, the huge slabs of rock that make up Earth’s rigid outer shell (see Plate tectonics). The trench formed as one large plate, called the Pacific Plate, collided with and slid beneath the neighboring Mariana Plate. Scientists call this process subduction. The subduction of the Pacific Plate causes the edges of both plates to flex downwards, forming the long trench.
Both the Pacific Plate and Mariana Plate are topped with oceanic crust, the kind of crust that makes up the ocean floor. The Pacific Plate subducts because it is denser than the Mariana Plate, due to the Pacific Plate’s extreme age. The crust of the Pacific Plate in this region formed about 170 million years ago, during the time of the dinosaurs. It is the oldest part of the Pacific Ocean floor. The process that formed the Mariana Trench also formed the Mariana Islands through subduction-induced volcanism. In this process, Earth’s interior heat causes the sinking rock to melt, forming magma. The magma rises through the overlying plate, erupting at the surface to form volcanoes. The Mariana Islands are the tops of seafloor volcanoes that have reached above the water’s surface.
The Mariana Trench was discovered in 1875 on the expedition of H.M.S. Challenger, a British ship that made a scientific study of the oceans and the ocean floor from 1872 to 1876. The Challenger Deep is named for the research vessel Challenger II, which discovered it using sounding (depth-measuring) equipment in 1951. Since its discovery, the Challenger Deep has been explored in several expeditions by piloted and robotic submarines.
Scientists have discovered hundreds of microorganisms that live on the seafloor at the trench. Other living things observed there include giant, single-celled creatures called xenophyophores << `zee` noh FY oh fawrz >>, amphipods (shrimplike creatures), and sea cucumbers. Food is scarce in the deep ocean. These animals survive by scavenging food that sinks from above. The animals that live in the Challenger Deep are adapted to the extreme pressure of the overlying water. This makes it impossible for them to survive outside of deep ocean trenches.
