The oceans cover nearly two-thirds of our planet and are its last great frontier for natural resources. The depths of the oceans and the ocean floor itself were of little interest until the middle of the last century when the first scientific deep-sea surveys were undertaken. The Challenger expedition nearly a hundred years ago discovered the existence of phosphorite and manganese dioxide concretions on the ocean floor, but these remained of purely scientific interest for many years. Although offshore mining of petroleum dates from 1899 and although undersea deposits of hard minerals, such as iron or coal, were mined even before

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