The Mariana Trench (also called the Marianas Trench) is the deepest part of the ocean. This trench lies in an area where two of the Earth's plates - the Pacific Plate and the Philippine Plate - come together.
The Pacific plate dives under the Philippine plate, which also partially gets pulled along (read more about this collision under oceanic-oceanic convergence here). It is also thought that water can be carried with it, and may contribute to strong earthquakes by hydrating rock and lubricating the plates, which might lead to a sudden slip. There are many trenches in the ocean, but because of the location of this trench, it is the deepest. The Mariana Trench is located in an area of old seafloor, made up of lava, which is dense and causes the seafloor to settle further. Plus, since the trench is so far away from any rivers, it does not get filled with sediment like many other oceanic trenches, which also contributes to its extreme depth.
The Mariana Trench is located in the western Pacific Ocean, east of the Philippines and about 120 miles east of the Mariana Islands. In 2009, President Bush declared the area surrounding Mariana Trench as a wildlife refuge, called the Marianas Trench Marine National Monument, which covers approximately 95,216 square miles - you can see a map here.
The trench is 1,554 miles long and 44 miles wide. The trench is more than 5 times wider than it is deep. The deepest point of the trench, which is known as the Challenger Deep - is almost 7 miles (10,994 meters) deep and is a bathtub-shaped depression. The trench is so deep that at the bottom that the water pressure is eight tons per square inch.
The water temperature in the deepest part of the ocean is a chilly 1 to 4 °C - just above freezing.
The bottom of deep areas like the Mariana Trench is composed of an "ooze" made up of the shells of plankton. While the trench and areas like it haven't been fully explored, we know that there are organisms that can survive at this depth, including bacteria, microorganisms, protists (foraminifera, xenophyophores, shrimp-like amphipods, and possibly even some fish. Voyages The first trip to the Challenger Deep was made by Jacques Piccard and Don Walsh in 1960. They didn't spend much time at the bottom, and couldn't see much as their sub kicked up too much sediment, but they did report seeing some flatfish. Voyages to the Mariana Trench have been made since then to map the area and collect samples, but humans had not been to the deepest point in the trench until 2012. In March 2012, James Cameron successfully completed the first solo, human mission to the Challenger Deep.