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[机经题库答案] 托福阅读生物类真题The Extinction of the Dinosaurs原文+题目汇总

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发表于 2017-5-9 17:52 |显示全部楼层
类别:生物类
真题151115CN-P4
Title:The Extinction of the Dinosaurs
Geologists define the boundary between sediment layers of the Cretaceous  period (144. C65 million years  ago) and the Paleocene period (65. C55 million years ago) in part by the types and amounts of rocks and fossils  they contain or lack.  

  
Before the limit of 65 million  years ago, marine strata are rich  in calcium carbonate due to accumulations of fossils of microscopic algae  deposited on the sea floor. Above the 65-million-year limit, sea-floor  sediments contain much less calcium carbonate, and fossils of several  families of mollusks are no longer found. In continental sediments, dinosaur  fossils, though frequent before 65 million years ago, are totally absent.  

  
By contrast, new families of mammals appear,  including large mammals for the first time.  Scientists wondered for many years about what could have caused the dinosaurs' rapid disappearance at the end of the  Cretaceous period, coming up with a great variety of theories and scenarios. For some, it could have been due to  unfavorable genetic changes triggered by a  dramatic increase by a factor of 10, 100,  1, 000 in cosmic-ray particles reaching the Earth after a supernova explosion somewhere in the  neighborhood of the solar system. For these  high-energy particles to affect life, they would have to get through the  protective barrier of the Earth's  magnetosphere, the region of the upper atmosphere controlled by Earth's magnetic field. That could have  happened if the cloud of particles from the  supernova explosion reached the Earth during a period when the  magnetosphere was weakened, something that may happen when the Earth's  magnetic field changes direction. And we know that  the magnetic north and south poles of the Earth switch on the average twice  every million years. However, this is not the only possible explanation for  dinosaur destruction.  

  
Other theories have raised the possibility of strong climate  changes in the tropics (but they  then must be explained). Certainly, if climate changes, the changed  distributions of temperature  and rainfall modify the conditions that favor one ecosystem over another. The  extinction of a particular family, genus, or species may result from a  complicated chain of indirect causes and effects. Over thirty years ago,  scientist Carl Sagan quoted one suggestion  that the demise of the dinosaurs resulted from the disappearance of a species  of fern plant that was important for dinosaur digestion. Other theories  involved a worldwide cold wave following the spread of a layer of cold but  not very salty water in the world's oceans,  which floated on the surface because, with its low salinity, the water was  less dense.  

  
Proponents of another theory that remains  under consideration today postulate that the  extinction of the dinosaurs corresponds to a period  of intense volcanic activity. It's not a question of just one or  even of a thousand eruptions comparable to the explosion of Krakatoa in 1883,  one of the largest volcanic events in modern times, but rather of a prolonged  period of activity. On the Deccan plateau in India, basalt (volcanic) rocks  cover more than 500, 000 square kilometers (nearly 200, 000 square miles),  and correspond to massive lava outflows occurring precisely at the end of the  Cretaceous. This sort of outflow could correspond to volcanic activity  similar to the activity that drives sea-floor spreading, with lava emerging  from elongated fractures in the crust rather than from craters.  

  
The volcanic convulsion that buried the Deccan plateau in lava  must also have changed the  composition of the atmosphere and severely affected climate. Initially, there  must have been strong sudden  cooling resulting from the blocking of sunlight by sulfate aerosol veils in the stratosphere  (part of the Earth's atmosphere). If strong cooling lasted a year after the  formation of the aerosols, it would have been the death of tropical species unable  to adapt to such a volcanic winter.  

  
However,  a long  period of strong volcanic activity (again,  remember thousands of Krakatoas) would  at the same time have added a substantial amount of carbon dioxide to the  atmosphere, reinforcing the greenhouse effect. This would gradually warm  things up, ending the extended cold snap and producing global warming  together with geographic shifts of humid and arid (dry) zones. Certainly  things would change to upset living conditions, leading to the extinction of  some species while others would profit, if only from the disappearance of predators.  

  
1. According  to paragraph 1, which of the following is true of Paleocene sediments
  
A.       They  lack fossils from some families of mammals found in Cretaceous sediments.  
B.         They contain fossils of dinosaurs.  
C.         They contain fossils of some animals that did  not exist during the Cretaceous.  
D.       They  contain fossils of more kinds of mollusks than are found in Cretaceous sediments.  

  
2. The  word unfavorable in the passage is closest in meaning to
  
A.       Unusual  
B.         Disadvantageous  
C.         Sudden
D.       major  

  
3. The  word triggered in the passage is closest in meaning to
  
A.       initiated
B.         intensified  
C.         followed
D.       aided  

  
4. Why  does the author include the information that the magnetic north and south  poles of the Earth switch on the  average twice every million years
  
A.        To provide  evidence showing that Earth's protective barrier is difficult to get through
B.         To show  that it is reasonable to think that particles from a supernova explosion  could have reached Earth  
C.         To explain  why some scientists believe a supernova explosion may have occurred near our solar system  
D.       To help explain why some scientists have  rejected the theory presented in paragraph 2  

  
5. According  to the theory discussed in paragraph 2,a weakening of  Earth's magnetosphere may have
  
A.        caused a supernova to explode near our solar system
B.         allowed gene-altering particles to reach  Earth's surface
C.         forced Earth's magnetic field to change direction  
D.       allowed  clouds of protective particles to escape from Earth's upper atmosphere

  
6. AII  of the following are mentioned in paragraph 3 as possible causes for the  extinction of the dinosaurs EXCEPT
  
A.        a change in the diet of dinosaurs  
B.         a change in the climate of the tropics
C.         a decrease in global temperatures  
D.       a  decrease in deep ocean salinity  

  
7. In  paragraph 3,why  does the author include the quotation by Carl Sagan
  
A.       To explain the connection between dinosaur  extinction and the extinction of other animal  species  
B.         To support  the claim about species extinction being due to indirect causes and effects  
C.         To show  that scientists have revised their ideas greatly in the last thirty years  
D.       To identify the differences between the various  theories for the extinction of dinosaurs  

  
8. According  to paragraph 4,what was one unusual aspect of the volcanic  activity at the end of the  Cretaceous
  
A.        Some explosions were much larger than Krakatoa.
B.         Eruptions occurred over a long period of  time.  
C.         Active volcanoes were sometimes separated by  many kilometers.  
D.       There  were active volcanoes in the sea as well as on land.  

  
9. Which  of the following is presented in paragraph 4 as evidence that intense  volcanic activity occurred at about  the time that the dinosaurs became extinct
  
A.        The size of the volcanic craters on the  Deccan plateau  
B.         An increase in sea-floor spreading  
C.         The formation in India of large amounts of a  type of rock associated with volcanoes  
D.       The  occurrence of a thousand or more volcanic explosions the size of Krakatoa  

  
10. The  word severely in the passage is closest in meaning to
  
A.       certainly  
B.         consequently  
C.         greatly  
D.       permanently  

  
11. The  word reinforcing in the passage is closest in meaning to
  
A.       making possible  
B.         spreading  
C.         introducing  
D.       strengthening

  
12. According  to paragraph 5,all  of the following are theorized to have occurred as a result of volcanic activity EXCEPT
  
A.        a decrease in the amount of sunlight reaching  Earth's surface  
B.         a reduction in the number of sulfate aerosol  veils in the stratosphere  
C.         increased dryness in some areas that were  once more humid  
D.       changes  in the atmosphere's composition resulting in an increase in temperature  

  
13.   Look at the four squares  that  indicate where the following sentence could be added to the passage.  
Thus,  ecosystems following periods of extensive volcanic activity necessarily had different combinations  of species than earlier ecosystems did.
Where  would the sentence best fit Click on a square to add the sentence to the passage.
(题目不完整)  

  
14. Drag  your choices to the spaces where they belong. To review the passage, click  on View Text    
Answer  Choices  
A.        Cosmic rays from a nearby supernova explosion  may have penetrated Earth's atmosphere, causing  genetic changes that dinosaur populations could not survive.  
B.         Climate changes in the tropics may have set  off a chain of indirect effects that negatively  affected the ecosystems in which dinosaurs  lived.  
C.         The spread of lava over  large part s of previously favored habitats such  as the Deccan Plateau may have made these  favored areas uninhabitable for many years.  
D.        Although the volcanic winter resulting from  the formation of sulfate aerosols eventually  ended, temperatures may have remained below levels required by dinosaurs to survive.  
E.         Temperature  changes and geographic shifts in climate zones due to the atmospheric effects of  volcanic activity may have been significant enough to cause extinction.  
F.         To be  convincing ,theories about what caused  dinosaurs to become extinct must be able to  explain the disappearance of other predators in the food chain at the same time
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