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Ocean floor

The Pacific Ocean floor Much of the ocean seems completely empty: a great expanse of featureless water, dotted with the occasional island. But beneath the waves it is a different picture. Between 4000 and 5000 metres (13,000–16,500 feet) down lies a dramatic landscape of vast abyssal plains, jagged mountains, erupting volcanoes and deep canyons. The undersea world amounts to nearly three-quarters of the Earth's surface—the plains beneath the Pacific Ocean alone cover about the same area as all the Earth’s land put together—yet hardly any of it has been explored.

Continental shelf

The continental shelf is part of a continental landmass that lies under water. An area of shallow, sunlit waters where most ocean life is found, the shelf usually extends up 50–100 kilometres (30–60 miles) out from the shore, although the Siberian continental shelf is 1500 kilometres (900 miles) wide. Here the water is no more than 200 metres (650 feet) deep.A block diagram showing a section of ocean floor, with typical features The continental shelf plunges steeply about 2000–2500 metres (6500–8000 feet) down the continental slope, then further down the less steep continental rise, to the abyssal plain. The steep continental slope marks the true boundary between ocean and continent.
Skeletons of diatoms, micro-organisms, rain down from surface waters to collect in the ooze on the abyssal plain.

Abyssal plain

The Mid-Oceanic Ridge, around 65,000 km (40,000 miles) in length, is the world's longest mountain range.

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