Voa Science Report - How a Revolution in Thought Shook Scientists' Understanding of Earth

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ONE: This is SCIENCE IN THE NEWS in VOA English. I'm Barbara Klein. VOICE TWO: And I'm Bob . Scientists who study the Earth tell us that the and ocean floors are always moving. Sometimes, this movement violent and might result in great destruction. VOICE ONE: we examine the process that causes earthquakes. (MUSIC) VOICE : The first pictures of Earth taken from space showed solid ball covered by brown and green land masses blue-green oceans. It appeared as if the Earth had looked that way ---- and always would. Scientists now , however, that the surface of the Earth is not permanent as had been thought. Scientists explain that the of our planet is always in motion. Continents move the Earth like huge ships at sea. They float pieces of the Earths outer skin, or crust. New is created as melted rock pushes up from inside planet. Old crust is destroyed as it rolls down the hot area and melts again. VOICE TWO: Only the nineteen sixties have scientists begun to understand that Earth is a great, living structure. Some experts say new understanding is one of the most important revolutions scientific thought. The revolution is based on the work scientists who study the movement of the continents ---- process called plate tectonics. Earthquakes are a result of process. Plate tectonics is the area of science that why the surface of the Earth changes and how changes cause earthquakes. VOICE ONE: Scientists say the surface the Earth is cracked like a giant eggshell. They the pieces tectonic plates. As many as twenty of cover the Earth. The plates float about slowly, sometimes into each other, and sometimes moving away from each . When the plates move, the continents move with them. the continents are above two plates. The continents split the plates move. VOICE TWO: Tectonic plates can cause as they move. Modern instruments show that about ninety of all earthquakes take place along a few lines several places around the Earth. These lines follow underwater where hot liquid rock flows up from deep inside planet. Sometimes, the melted rock comes out with a burst of pressure. This forces apart pieces of the surface in a violent earthquake. Other earthquakes take place the edges of continents. Pressure increases as two plates against each other. When this happens, one plate moves the other, suddenly causing the Earths surface to split. ONE: One example of this is found in California, the West Coast of the United States. One part California is on what is known as the Pacific . The other part of the state is on what known as the North American plate. Scientists say the plate is moving toward the northwest, while the North plate is moving more to the southeast. Where these huge plates come together is called a fault line. name of this line between the plates in California the San Andreas Fault. It is along or near line that most of Californias earthquakes take place, as two tectonic plates move in different directions. The city Los Angeles in Southern California is about fifty kilometers the San Andreas Fault. Many smaller fault lines can found throughout the area around Los Angeles. A major in nineteen ninety-four was centered along one of these fault lines. (MUSIC) VOICE TWO: The story of plate begins with the German scientist Alfred Wegener in the part of the twentieth century. He first proposed that continents had moved and were still moving. He said idea came to him when he observed that the of South America and Africa could fit together like pieces of a puzzleHe proposed that the two continents have been one, then split apart. Later, Alfred Wegener the continents had once been part of a huge of land he called Pangaea. He said the huge had split more than two hundred million years ago. said the pieces were still floating apart. VOICE ONE: investigated the idea that continents move. He pointed out line of mountains that appears from east to west South Africa. Then he pointed out another line of that looks almost exactly the same in Argentina, on other side of the Atlantic Ocean. He found fossil of the same kind of an early plant in of Africa, South America, India, Australia and even Antarctica. Wegener said the mountains and fossils were evidence that the land on Earth was united at some time the distant past. VOICE TWO: Wegener also noted differences the continents and the ocean floor. He said the were more than just low places that had filled water. Even if the water was removed, he said, person would still see differences between the continents and ocean floor. Also, the continents and the ocean floor not made of the same kind of rock. The are made of a granite-like rock, a mixture of and aluminum. The ocean floor is basalt rock, a of silicon and magnesium. Mister Wegener said the lighter rock floated up through the heavier basalt rock of ocean floor. VOICE ONE: Support for Alfred Wegeners ideas not come until the early nineteen-fifties-. American scientists Harry and Robert Dietz said the continents moved as new floor was created under the Atlantic Ocean. They said thin valley in the Atlantic Ocean was a place the ocean floor splits. They said hot melted material up from deep inside the Earth through the split. the hot material reaches the ocean floor, it spreads , cools and hardens. It becomes new ocean floor. The scientists proposed that the floor of the Atlantic Ocean moving away from each side of the split. The is very slow ---- a few centimeters a year. time, they said, the moving ocean floor is blocked it comes up against the edge of a continent. it is forced down under the continent, deep into Earth, where it is melted again. Harry Hess and Dietz said this spreading does not make the Earth . As new ocean floor is created, an equal amount destroyed. VOICE TWO: The two scientists also said Alfred was correct. The continents move as new material from center of the Earth rises, hardens and pushes older of the Earth away from each other. The continents moving all the time, although we cannot feel it. called their theory "sea floor spreading." The theory explains as the sea floor spreads, the tectonic plates are and pulled in different directions. (MUSIC) VOICE ONE: The of plate tectonics explains volcanoes as well as earthquakes. of the world's volcanoes are found at the edges plates, where geologic activity is intense. The large number volcanoes around the Pacific plate has earned the name " of Fire." Volcanoes also are found in the middle plates, where there is a well of melted rock. call these wells "hot spots." A hot spot does move. However, as the plate moves over it, a of volcanoes is formed. The Hawaiian Islands were created the middle of the Pacific Ocean as the plate slowly over a hot spot. This process is continuing, the plate continues to move. VOICE TWO: Volcanoes and are among the most frightening events that nature can . The major earthquake in South Asia in October of thousand five, for example, killed more than seventy thousand . More than three million people were made homeless because the earthquake. At times like these, we remember that ground is not as solid and unchanging as people like to think. (MUSIC) VOICE ONE: SCIENCE IN THE was written by Nancy Steinbach. Cynthia Kirk was our . Im Barbara Klein. VOICE TWO: And Im Bob Doughty. users can read and listen to our programs at .. Join us again next week for more news about in Special English on the Voice of America.

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