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The ocean bottom is divided into three major areas: the continental shelf, the continental slope, and the deep ocean basin.
The continental shelf extends underwater from each of the major land masses. It is the submerged portion of the continents. The shelf has features similar to those we see on land, including hills, ridges, and canyons.
The size of the shelf varies. It may be virtually non-existent in some areas; elsewhere it may extend from shore for several hundred miles. The shelf’s average distance is about 64 kilometers (40 mi).
It is beyond the continental shelf that the “deep sea” begins. The shelf ends at a depth of about 200 meters (660 ft), giving way to the steeper continental slope, which descends about 3,700 meters (12,000 ft) to the deep ocean basin.
Here, the ocean floor deepens sharply and its features again resemble those on land, only on a much larger scale, with great plains and mountains.
In fact, the Earth’s longest mountain range lies under the sea. Over 56,000 kilometers (35,000 mi) long, this mountain range, called the Mid-Ocean Ridge system, snakes its way around the globe.
The Mid-Ocean Ridge marks the areas where the Earth’s crustal plates are moving apart. It is one of the most geologically active areas on Earth. It is where new seafloor is being born, giving rise to hydrothermal vents and volcanoes.
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