Wegener said the mountains and fossils were evidence that all the land on Earth was united at some time in the distant past.
STEVE EMBER: Wegener also noted differences between the continents and the ocean floor. He said the oceans were more than just low places that had filled with water. Even if the water was removed, he said, a person would still see differences between the continents and the ocean floor.
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’s surface. The ocean floor is basalt rock, a mixture of silicon and magnesium. Mister Wegener said the lighter continental rock floated up through the heavier basalt rock of the ocean floor.
FAITH LAPIDUS: Support for Alfred Wegener’s ideas did not come until the early nineteen-fifties. 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 Ocean 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 two scientists proposed that the floor of the Atlantic Ocean is moving away from each side of the split. 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.
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2013-11-25
2013-11-25
2013-11-25
2013-11-25
2013-11-25
2013-11-25