2014年英语四级听力的练习：VOA慢速4.8(1)_大学英语听力

2014年英语四级听力的练习：VOA慢速4.8(1)

　　Also, the continents and the ocean floor are not made of the same kind of rock.

　　The continents are made of a granite-like rock. Granite is made when hot, liquid rock cools and hardens under the Earth surface. The ocean floor is basalt rock, a mixture of silicon and magnesium.

　　The German scientist said the lighter continental rock floated up through the heavier basalt rock of the ocean floor.

　　Support for Mr. Wegener ideas did not come until the 1950s. Two American scientists found that the continents moved as new sea floor was created under the Atlantic Ocean. Harry Hess and Robert Dietz said a thin valley in the Atlantic was a place where the ocean floor splits. They said hot melted material flows up from deep inside the Earth through the split. As the hot material reaches the ocean floor, it spreads out, cools and hardens. It becomes new ocean floor.

　　The Americans proposed that the floor of the Atlantic Ocean is moving away from each side of the split and expanding. The movement is very slow -- a few centimeters a year. In time, they said, the moving ocean floor is blocked when it comes up against the edge of a continent. Then it is forced down under the continent, deep into the Earth, where it is melted again. Harry Hess said the Pacific Ocean was getting smaller.