Covered by water and unnoticed by most, the ocean is full of hidden geologic features. While much of the ocean floor is relatively flat, the ocean is home to the tallest mountains in the world, when measured from the base at the ocean floor, and the deepest canyons in the world. The deepest spot on Earth is the Mariana Trench.
Located just east of the 14 Mariana Islands, the Mariana Trench, at its deepest point, is nearly 11,000 meters, or 36,000 feet deep. The deepest portion of the Mariana Trench is called the Challenger Deep. It is so named after the British Naval Vessel Challenger whose crew discovered it in 1951. The Challenger Deep is located 210 miles southwest of Guam.
The trench, like all of the most dramatic features on Earth was formed through the mechanism of plate tectonics.
Plate tectonics changes the Earth over long periods of time. The surface of the Earth is covered with plates of crust material that move over the underlying mantle. The mantle is solid but it moves slowly over geological times, millions of years. The surface, or crust, floats on top of the mantle. At certain locations in the center of the oceans the crust is pushed apart at what are known to geologists as oceanic ridges.
Where two plates meet one is pushed under the other in what is called a subduction zone. Depending on the materials of each plate what happens at this convergence varies. The Mariana trench was formed by an ocean-to-ocean subduction zone, which is where two plates of oceanic material meet and one is forced under the other. The Mariana Trench is where the Pacific plate pushes underneath the Philippine Plate. The dipping of the Pacific Plate at the edge of the Philippine Plate is what has formed the trench.
When one tectonic plate is forced deep into the Earth, some of the materials are melted and come to the surface and form volcanoes. The volcanoes from this geologic activity are what have formed the Mariana Islands. The U.S. territory of Guam is the southernmost of the Mariana Islands.
The United States Navy’s manned bathyscaphe, Trieste, dove to the bottom of the Mariana Trench in 1960. This dive will stand in the record books as the deepest dive ever made unless another, deeper, location is located in the world’s oceans. A Swiss scientist, Swiss scientist Jacques Piccard, and a U.S. Naval officer, Lt. Donald Walsh, were onboard for this visit to the deepest spot on Earth.
This descent, and later descents by unmanned submersibles, has given us a limited understanding of what is probably the least unexplored place on Earth. We know more about vast stretches of other planets than we know about the deepest parts of the ocean.
The deepest part of the ocean is called the Abyssal Zone. While no light can penetrate to these depths, and therefore no plants can grow, life still exists. Hydrothermal vents deep in the Mariana Trench support life of which we have only recently become aware. The hot water and chemicals that are released by these vents support bacteria, which are in turn consumed by crabs and other organisms that have evolved to survive in these extreme conditions.
Even in the cold depths of the trench, away from the vents, life survives. Extremophile bacteria and fungi live off the detritus that falls down from above. As organisms from the higher levels of the oceans die they settle to the depths providing nutrients to a wide array of life.
At such depths and pressures even the chemical processes that allow for life are changed. Enzymes don’t work the same as at lower pressures and the proteins that make up cell membranes behave differently. The life at these depths is truly different from life more shallow in the oceans. The extreme heat of the hydrothermal vents and the extreme cold of the ocean depths also result in some forms of life that can survive both hot and cold conditions, a rarity anywhere else on Earth.
But, even in these conditions organisms similar to those found throughout the oceans survive. The unmanned Japanese submersible Kaiko found shrimp, worms and sea cucumbers in some of the deepest parts of the Mariana Trench. And, while no photographs have been taken and no samples have been recovered, Piccard was said to have seen a fish just above the bottom of the trench on the 1960 descent.
As a place that has had fewer visitors than the Moon, the deepest place in the ocean certainly has more secrets to be uncovered. The Mariana Trench is a strange and fascinating place that is worth studying more.