托福阅读常考话题及练习题推荐一：恐龙大灭绝（3）

1托福阅读常考话题-恐龙大灭绝练习题

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 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.

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.

A. The fossil record suggests that there was an abrupt extinction of many plants and animals at the end of the Mesozoic era.

B. Few fossils of the Mesozoic era have survived in the rocks that mark the end of the Cretaceous.

C. 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.

D. 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 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 (Ir) it contained.

8. In paragraph 4, all the following questions are answered EXCEPT:

A. Why is there a layer of clay between the rocks of the Cretaceous and Cenozoic?

B. Why were scientists interested in determining how long it took to deposit the layer of clay at the end of the retaceous?

C. What was the effect of the surprising observation scientists made?

D. Why did scientists want more information about the dinosaur extinctions at the end of the Cretaceous?

Paragraph 5: Ir 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. Ir 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 Ir 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 Ir seems to require a special explanation.

9. The word “bombard” in the passage is closest in meaning to

A. approach

B. strike

C. pass

D. circle

10. Paragraph 5 implies that a special explanation of Ir in the boundary clay is needed because

A. the Ir in microscopic meteorites reaching Earth during the Cretaceous period would have been incorporated into Earth’s core

B. the Ir in the boundary clay was deposited much more than a million years ago

C. the concentration of Ir in the boundary clay is higher than in microscopic meteorites

D. the amount of Ir 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 long-term 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

A. exhaustion

B. disturbance

C. modification

D. disappearance

12. Paragraph 6 mentions all of the following effects of the hypothesized asteroid collision

A. a large dust cloud that blocked sunlight

B. an immediate drop in the surface temperatures of the continents

C. an extreme decrease in rainfall on the continents

D. a long-term increase in global temperatures

Paragraph 5: Ir 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. Ir 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 Ir 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 Ir 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 Ir in the boundary clay came from microscopic meteorites cannot be accepted. Where would the sentence best fit?

14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important

ideas in the passage. Some sentences do not belong in the summary because they express that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. For a long time scientists have argued that the extinction of the dinosaurs was related to climate change.

Answer choices

A. A simple climate change does not explain some important data related to the extinction of the dinosaurs at the end of the Cretaceous.

B. The retreat of the seaways at the end of the Cretaceous has not been fully explained.

C. The abruptness of extinctions at the end of the Cretaceous and the high concentration of Ir found in clay deposited at that time have fueled the development of a new hypothesis.

D. Extreme changes in daily and seasonal climates preceded the retreat of the seas back into the major ocean basins.

E. Some scientists hypothesize that the extinction of the dinosaurs resulted from the effects of an asteroid collision with Earth.

F. Boundary clay layers like the one between the Mesozoic and Cenozoic are used by scientists to determine the rate at which an extinct species declined.