5 Deepest Oceans

Edited by Kathy McGraw, Maria Quinney

Covering more than 71 percent of the Earth's surface, an incredible 99 percent of the living space on the planet is contained in them. Yet, for all of that, we still know so little, having explored less than 5 percent. We have explored more of the moon's surface than we have the oceans! From the Mid-Oceanic Ridge which divides the Atlantic Ocean into two to the depths of the Challenger Deep at the bottom of the Pacific Ocean, the salty depths of the world's oceans remain a mystery to humanity. Here are the world's oceans, ranked by depth:

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  1. 1
    Pacific Ocean
    The Pacific Ocean is not only the deepest ocean, with an average depth of 13,740 feet (4,188 meters), but it also contains the deepest point on the planet, at 36,070 feet (10,994 meters). The Challenger Deep is part of the Mariana Trench, a deep groove in the sea floor where one tectonic plate is being subducted under another tectonic plate. The water here is deep enough to cover the top of Mount Everest miles below the surface!
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  2. 2
    Atlantic Ocean
    Coming in as the second deepest ocean is the Atlantic, with an average depth of 12,254 feet (3,735 meters). The deepest part of the Atlantic is the Milwaukee Deep of the Puerto Rico Trench, which lies 28,374 feet (8,648 meters) below the waves. This subduction zone was responsible for the 8.1 magnitude earthquake that struck the region in 1953 and the subsequent tsunami.
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  3. 3
    Indian Ocean
    Although the Indian Ocean has a slightly deeper average depth than the Atlantic, at 12,740 feet (3,883 meters), it is still the third deepest because its deepest point comes in at 24,460 feet (7,455 meters). This point is located in, you guessed it, another trench, the Sunda (also known as the Java Trench).
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  4. 4
    Southern Ocean
    Created by the International Hydrographic Organization in 2000, the Southern Ocean is the world's newest named ocean. It is composed of the southernmost portions of the Pacific, Atlantic, and Indian Oceans, or in other words, all of the waters surrounding Antarctica. It comes in the fourth deepest ocean, with its lowest point in the South Sandwich Trench at 23,737 feet (7,236 meters).
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  5. 5
    Arctic Ocean
    The fifth deepest ocean, the Arctic Ocean has an average depth of 3.407 feet (1,038 meters). It is mostly covered by ice all year around. Its deepest point is the Eurasia Basin, one of the two basins created by the Lomonosov Ridge, which bisects this ocean. The Eurasia Basin has a depth of 17,881 feet (5,450 meters).
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Why Are the Oceans So Deep?

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To explain why the oceans are deep, it is necessary to go into a little geology. The Earth's crust is composed of two main materials, granite and basalt, and is broken up into several tectonic plates which "float" on the asthenosphere. The asthenosphere is the upper portion of the mantle, which lies roughly 50 to 120 miles beneath the lithosphere (crust) and is so-named because it has the consistency of soft plastic, kind of like silly putty, only with more flow. Granitic crust is lighter and less dense than is basaltic crust, so basaltic crust "rides" lower on the asthenosphere than does granitic crust, forming the lowest parts of the Earth's surface, which we call the oceans.

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But that's not the whole story: there are yet deeper parts of the ocean floor, known as oceanic trenches. Trenches form wherever one plate has been pulled under another, forming one type of plate boundary known as a subduction zone. Active subduction zones cause the majority of the Earth's largest seismic events, such as the 1964 Alaskan earthquake, which measured 9.2 on the Richter scale, caused by the shifting of the Pacific Plate being pulled under the North American Plate in the Aleutian Trench. An even larger earthquake happened in 1960 Chile, measuring 9.5 on the Richter scale, as a result of the Nazca Plate subducting under the South American Plate.

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Earthquakes and Volcanoes Oh My

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The plate boundaries of the world give rise not only to earthquakes but to volcanoes as well. In fact, the most seismically active areas in the world surround the Pacific Ocean. Known as the Ring of Fire, it is composed of a series of subduction zones where the basaltic crust of the ocean floor is being pulled under the lighter granitic crust of the surrounding continents. There are more than 450 volcanoes along the Ring of Fire, including Mount Pinatubo in the Philippines, Mount Fuji in Japan, and Mount Saint Helens in the Pacific North Western United States. The San Andreas Fault is also part of this system, connecting the expanding East Pacific Rise ridge system off Baja California with the Cascadia Subduction Zone off the Oregon and Washington coasts.

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Another type of plate boundary is found underneath the Atlantic Ocean: the Mid-Atlantic Ridge, which forms the boundary between the North American and Eurasian Plates in the north and the South American and African Plates in the south. The ridge is called a divergent plate boundary because the plates are moving away from each other with the new oceanic (basaltic) crust being created. Hot magma from the Earth's mantle spills out along the edges, rapidly cools, and forms new crust in a "gentle" volcanism of the type seen in Iceland, which is, in fact, part of this ridge system. The farther away from either side of the ridge you travel, the older the crust gets.

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Exploring the Deepest Part of the Ocean

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Imagine being surrounded by the inky blackness of an endless night, a darkness unrelieved by even the weakest light of the most distant stars. It's a blackness so perfect that your eyes can't adjust; you are blind without artificial light. Imagine further that miles and miles of ocean water rise above you and that the weight of the water plus the air above the waves equals 1,110 atmospheres, a pressure that is 1,000 times that at sea level. That is what conditions are like at the bottom of the Challenger Deep, seven miles below the surface of the Pacific Ocean, which makes it very difficult for humans to get down to, much less explore.

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To date, there have been only two manned expeditions to the bottom of the Challenger Deep. The first was done on January 23, 1960, when Jacques Piccard and Don Walsh descended to a depth of 37,797 feet (10,911 meters) in the bathyscaphe Trieste. The two men stayed at the bottom for about 20 minutes after a dive that took over four hours.

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Director James Cameron of the Titanic and Abyss movie fame conducted the second and last manned expedition to the bottom of the Challenger Deep on March 26, 2012. Cameron descended to a depth of 7 miles (11 kilometers) in his one-man submersible, the Deepsea Challenger. The dive took a little over two and half hours, after which Cameron was able to spend about two hours down on the bottom. Unlike the Trieste, which could only move vertically, Cameron's Deepsea Challenger was able to move around, and he was able to collect several specimens to take with him back to the surface.

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Facts About the Deep Ocean

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  • Sunlight penetrates only the first 3,000 feet of ocean water
  • The record for the deepest Scuba dive is 1,000 feet down
  • Sperm Whales have been known to dive 9,000 feet down and are the deepest diving mammal
  • The wreck of the RMS Titanic sits in 12,460 feet of water
  • The oceans support 50 percent of the Earth's species
  • There is enough salt in the oceans to cover all of the continents to a depth of five feet
  • The temperature In the deep ocean is 39 Fahrenheit
  • The speed of sound is five times faster in water than it is on land
  • Life began in the oceans about 3.1 to 3.4 billion years ago
  • Xenophyophores are a species of foraminifera, which are amoeba -like creatures, that thrive in the inhospitable waters of the Challenger Deep

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Categories : Travel & Leisure

Recent edits by: Kathy McGraw

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