Text B. Scientific Problems
1. Explaining the formation of coral island has long been a problem for scientists. 2. In 1831, a famous English scientist, Charles Darwin (1809-1882), sailed on a five-year scientific expedition around the world. During his journey, Darwin studied coral islands. In Darwin’s time it was known that coral islands were made of limestone, a rock made of calcium carbonate. However none knew exactly how coral islands were formed. 3. Darwin became curious about how the coral islands were formed. To help solve the problem, he examined samples of island material withdrawn from deep beneath the ocean surface. Darwin discovered coral rock on a depth of 18m below sea level. From 18 m to 54 m he found mixtures of coral and sand. Below 54 m, there was no coral. Instead, there was sand, rock and mud. 4. Based on these observations, Darwin formed a hypothesis. He believed that coral islands were not built upward starting at the ocean floor. If the coral islands had been built upward from the ocean floor, he should have discovered coral at every depth.* 5. Darwin’s hypothesis was that coral islands were formed on the circular ridges of extinct volcanoes. A coral island formed as a volcano slowly rose to the surface of the ocean over a long period of time. Coral animals attached themselves to the circular rim of the volcano. Through time, the extinct volcano slowly sank. As it sank, coral rock built up along the rim forming a ring-shaped island. This island-building process has taken hundreds of thousands of years!
* Если бы коралловые острова формировались на дне океана, он бы обнаружил присутствие кораллов на всех глубинах.
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