Marine waters cover 70.8% of the earth’s surface. And, if we substract the 5.5% area of the continental shelf, 65.3% of the earth’s surface is occupied by continental slope and rise, and deep-sea parts (data after Dietrich and Kalle 1957). The deep sea can be subdivided into several topographical units. There are deep-sea grabens<span> (15 in number), which cut deeper than 6,000 m. Deep-sea grabens are restricted to tectonic active regions near the foot of continental slopes.</span>
<span>Although China's agricultural output is the largest in the world, only about 15% of its total land area can be cultivated. China's arable land, which represents 10% of the total arable land in the world, supports over 20% of the world's population. </span>
The Arctic ocean is the smallest of the world's five oceans
The Nile River was used by the ancient Egyptian,It<span> was also used to transport items to the other parts of the Egyptian kingdom.
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