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  3. Our knowledge of the oceans hundreds of years ago was confined to the two-dimensional shape of the sea surface and the hazards o

Our knowledge of the oceans hundreds of years ago was confined to the two-dimensional shape of the sea surface and the hazards o

admin2016-11-13  66
问题     Our knowledge of the oceans hundreds of years ago was confined to the two-dimensional shape of the sea surface and the hazards of navigation presented by the irregularities in depth of the shallow water close to the land. The open sea was deep and mysterious, and anyone who gave more than a passing thought to the bottom confines of the oceans probably assumed that the sea bed was flat. Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1839, but it was not until 1869, when H.M.S. Porcupine was put at the disposal of the Royal Society for several cruises, that a series of deep soundings was obtained in the Atlantic and the first samples were collected by dredging (挖掘) the bottom. Shortly after this the famous H.M.S. Challenger expedition established the study of the sea-floor as a subject worthy of the most qualified physicists and geologists. A burst of activity associated with the laying of submarine cables soon confirmed the Challenger’s observation that many parts, of the ocean were two to three miles deep, and the existence of underwater features of considerable magnitude.
    Today, enough soundings are available to enable a relief map of the Atlantic to be drawn and we know something of the great variety of the sea bed’s topography (地形). Since the sea covers the greater part of the earth’s surface, it is quite reasonable to regard the sea floor as the basic form of the crust of the earth, with, superimposed upon, it the continents, together with the islands and other features of the oceans. The continents form rugged tablelands which stand nearly three miles above the floor of the open ocean. From the shore line, out a distance which may be anywhere from a few miles to a few hundred miles, runs the gentle slope of the continental shelf, geologically part of the continents. The real dividing line between continents and oceans occurs at the foot of a steeper slope.
    This continental slope usually starts at a place somewhere near the 100-fathom mark and in the course of a few hundred miles reaches the true ocean floor at 2,500-3,500 fathoms. The slope averages about 1 in 30, but contains steep, probably vertical, cliffs, and gentle sediment-covered terraces, and near its lower reaches there is a long tailing-off which is almost certainly the result of material transported out to deep water after being eroded from the continental masses.
The H.M.S. Challenger expedition
选项 A、was devoted to dredging the ocean.
B、was dedicated to laying submarine cables.
C、gave the sea-floor study disciplinary independence.
D、obtained a series of deep soundings in the Atlantic.
答案C
解析 根据题干的H．M．S．Challenger expedition定位到第1段倒数第2句。该句指出：“‘挑战者’号舰船对海底进行了考察，把对海床的研究确立为一个值得一流物理学家和地质学家从事的研究课题。”由此可见，正是这次考察使得海床研究成为了独立的学科。故C为本题答案。A显然张冠李戴，文中明确指出，英国“豪猪”号舰船通过挖掘获得了首批海底样品，排除A；铺设海底电缆的热潮发生在“挑战者”号舰船考察之后，并证明了“挑战者”号考察的结果，故B也排除；测得大西洋水深的是“豪猪”号舰船，不是“挑战者”号，故D也排除。
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