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10. Paragraph 5 implies that a special explanation of lr in the boundary clay is needed because ○the lr in microscopic meteorites reaching Earth during the Cretaceous period would have been incorporated into Earth’s core ○the lr in the boundary clay was deposited much more than a million years ago
○the concentration of lr in the boundary clay is higher than in microscopic meteorites
○the amount of lr in the boundary clay is too great to have come from microscopic meteorites during the time the boundary clay was deposited
Paragraph 6: In view of these facts, scientists hypothesized that a single large asteroid, about 10 to 15 kilometers across, collided with Earth, and the resulting fallout created the boundary clay. Their calculations show that the impact kicked up a dust cloud that cut off sunlight for several months, inhibiting photosynthesis in plants; decreased surface temperatures on continents to below freezing; caused extreme episodes of acid rain; and significantly raised longterm global temperatures through the greenhouse effect. This disruption of food chain and climate would have eradicated the dinosaurs and other organisms in less than fifty years. 11. The word disruption in the passage is closest in meaning to ○exhaustion
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12. Paragraph 6 mentions all of the following effects of the hypothesized asteroid collision EXCEPT ○a large dust cloud that blocked sunlight
○an immediate drop in the surface temperatures of the continents
○an extreme decrease in rainfall on the continents
○a longterm increase in global temperatures
Paragraph 5: It 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. ■
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
Consequently, the idea that the lr in the boundary clay came from microscopic meteorites cannot be accepted.
Where would the sentence best fit?
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- Fall '13