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Unformatted text preview: it took to deposit the clay by determining the amount of the element iridium (lr) it contained.
7. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? In correct choices change the meaning in important ways or leave out essential information. ○The fossil record suggeststhat there was an abrupt extinction of many plants and animals at the end of the Mesozoic era. ○Few fossils of the Mesozoic era have survived in the rocks that mark the end of the Cretaceous.
○Fossils from the Cretaceous period of the Mesozoic up to the beginning of the Cenozoic era have been removed from the layers of rock that surrounded them. ○Plants and animals from the Mesozoic era were unable to survive in the Cenozoic era.
Paragraph 4: Dissatisfaction with conventional explanations for dinosaur extinctions led to a surprising observation that, in turn, has suggested a new hypothesis. Many plants and animals disappear abruptly from the fossil record as one moves from layers of rock documenting the end of the Cretaceous up into rocks representing the beginning of the Cenozoic (the era after the Mesozoic). Between the last layer of Cretaceous rock and the first layer of Cenozoic rock, there is often a thin layer of clay. Scientists felt that they could get an idea of how long the 252
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extinctions took by determining how long it took to deposit this one centimeter of clay and they thought they could determine the time it took to deposit the clay by determining the amount of the element iridium (lr) it contained. 8. In paragraph 4, all the following questions are answered EXCEPT: ○Why is there a layer of clay between the rocks of the Cretaceous and Cenozoic?
○Why were scientists interested in determining how long it took to deposit the layer of clay at the end of the Cretaceous? ○What was the effect of the surprising observation scientists made?
○Why did scientists want more information about the dinosaur extinctions at the end of the Cretaceous?
Paragraph 5: lt has not been common at Earth’s since the very beginning of the planet’s history. Because it usually exists in a metallic state, it was preferentially incorporated in Earth’s core as the planet cooled and consolidated. lr is found in high concentrations in some meteorites, in which the solar system’s original chemical composition is preserved. Even today, microscopic meteorites continually bombard Earth, falling on both land and sea. By measuring how many of these meteorites fall to Earth over a given period of time, scientists can estimate how long it might have taken to deposit the observed amount of lr in the boundary clay. These calculations suggest that a period of about one million years would have been required. However, other reliable evidence suggests that the deposition of the boundary clay could not have taken one million years. So the unusually high concentration of lr seems to require a special explanation.
9. The word bombard in the passage is closest in meaning to ○approach
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This note was uploaded on 09/17/2013 for the course LANGUAGE 13DL208 taught by Professor Wang during the Fall '13 term at East China Normal University.
- Fall '13