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1、TPO15Passage2-+ TPO15Passage2- Mass Extinctions Cases in which many species become extinct within a geologically short interval of time are called mass extinctions. There was one such event at the end of the Cretaceous period (around 70 million years ago). There was another, even larger, mass extinc
2、tion at the end of the Permian period (around 250 million years ago). The Permian event has attracted much less attention than other mass extinctions because mostly unfamiliar species perished at that time. The fossil record shows at least five mass extinctions in which many families of marine organ
3、isms died out. The rates of extinction happening today are as great as the rates during these mass extinctions. Many scientists have therefore concluded that a sixth great mass extinction is currently in progress. What could cause such high rates of extinction? There are several hypotheses, includin
4、g warming or cooling of Earth, changes in seasonal fluctuations or ocean currents, and changing positions of the continents. Biological hypotheses include ecological changes brought about by the evolution of cooperation between insects and flowering plants or of bottom-feeding predators in the ocean
5、s. Some of the proposed mechanisms required a very brief period during which all extinctions suddenly took place; other mechanisms would be more likely to have taken place more gradually, over an extended period, or at different times on different continents. Some hypotheses fail to account for simu
6、ltaneous extinctions on land and in the seas. Each mass extinction may have had a different cause. Evidence points to hunting by humans and habitat destruction as the likely causes for the current mass extinction. American paleontologists David Raup and John Sepkoski, who have studied extinction rat
7、es in a number of fossil groups, suggest that episodes of increased extinction have recurred periodically, approximately every 26 million years since the mid- Cretaceous period. The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more drastic in a whole series of such r
8、ecurrent extinction episodes. The possibility that mass extinctions may recur periodically has given rise to such hypotheses as that of a companion star with a long-period orbit deflecting other bodies from their normal orbits, making some of them fall to Earth as meteors and causing widespread deva
9、station upon impact. Of the various hypotheses attempting to account for the late Cretaceous extinctions, the one that has attracted the most attention in recent years is the asteroid-impact hypothesis first suggested by Luis and Walter Alvarez. According to this hypothesis, Earth collided with an a
10、steroid with an estimated diameter of 10 kilometers, or with several asteroids, the combined mass of which was comparable. The force of collision spewed large amounts of debris into the atmosphere, darkening the skies for several years before the finer particles settled. The reduced level of photosy
11、nthesis led to a massive decline in plant life of all kinds, and this caused massive starvation first of herbivores and subsequently of carnivores. The mass extinction would have occurred very suddenly under this hypothesis. One interesting test of the Alvarez hypothesis is based on the presence of
12、the rare-earth element iridium (Ir). Earths crust contains very little of this element, but most asteroids contain a lot more. Debris thrown into the atmosphere by an asteroid collision would presumably contain large amounts of iridium, and atmospheric currents would carry this material all over the
13、 globe. A search of sedimentary deposits that span the boundary between the Cretaceous and Tertiary periods shows that there is a dramatic increase in the abundance of iridium briefly and precisely at this boundary. This iridium anomaly offers strong support for the Alvarez hypothesis even though no
14、 asteroid itself has ever been recovered. An asteroid of this size would be expected to leave an immense crater, even if the asteroid itself was disintegrated by the impact. The intense heat of the impact would produce heat-shocked quartz in many types of rock. Also, large blocks thrown aside by the
15、 impact would form secondary craters surrounding the main crater. To date, several such secondary craters have been found along Mexicos Yucatan Peninsula, and heat-shocked quartz has been found both in Mexico and in Haiti. A location called Chicxulub, along the Yucatan coast, has been suggested as t
16、he primary impact site. Paragraph 1: Cases in which many species become extinct within a geologically short interval of time are called mass extinctions. There was one such event at the end of the Cretaceous period (around 70 million years ago). There was another, even larger, mass extinction at the
17、 end of the Permian period (around 250 million years ago). The Permian event has attracted much less attention than other mass extinctions because mostly unfamiliar species perished at that time. TPO15Passage2 1. Paragraph 1 supports which of the following statements about mass extinctions? They tak
18、e place over a period of 70 million years. They began during the Cretaceous period. They eliminate many animal species that exist at the time they occur. They occur every 250 million years. Paragraph 2: The fossil record shows at least five mass extinctions in which many families of marine organisms
19、 died out. The rates of extinction happening today are as great as the rates during these mass extinctions. Many scientists have therefore concluded that a sixth great mass extinction is currently in progress. 2. According to paragraph 2, scientists base their belief that a mass extinction is going
20、on at present on which of the following? The speed with which mass extinctions are happening today is similar to the speed of past extinctions. The number of species that have died out since the last extinction event is extremely large. Mass extinctions occur with regularity and it is time for anoth
21、er one. Fossil records of many marine species have disappeared. Paragraph 3: What could cause such high rates of extinction? There are several hypotheses, including warming or cooling of Earth, changes in seasonal fluctuations or ocean currents, and changing positions of the continents. Biological h
22、ypotheses include ecological changes brought about by the evolution of cooperation between insects and flowering plants or of bottom-feeding predators in the oceans. Some of the proposed mechanisms required a very brief period during which all extinctions suddenly took place; other mechanisms would
23、be more likely to have taken place more gradually, over an extended period, or at different times on different continents. Some hypotheses fail to account for simultaneous extinctions on land and in the seas. Each mass extinction may have had a different cause. Evidence points to hunting by humans a
24、nd habitat destruction as the likely causes for the current mass extinction. 3. The word extended in the passage is closest in meaning to specific unlimited reasonable long 4. According to paragraph 3, each of the following has been proposed as a possible cause of mass extinctions EXCEPT habitat des
25、truction continental movement fierce interspecies competition changes in Earths temperature 5. Paragraph 3 supports which of the following ideas about mass extinctions? Scientists know the exact causes of most mass extinctions. Mass extinctions are unlikely to happen again in the future. Insects, fl
26、owering plants, and bottom-feeding predators in the oceans tend to be the first organisms to disappear during episodes of mass extinctions. Some mass extinctions occurred on land and in the seas at the same time. Paragraph 4: American paleontologists David Raup and John Sepkoski, who have studied ex
27、tinction rates in a number of fossil groups, suggest that episodes of increased extinction have recurred periodically, approximately every 26 million years since the mid-Cretaceous period. The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more drastic in a whole serie
28、s of such recurrent extinction episodes. The possibility that mass extinctions may recur periodically has given rise to such hypotheses as that of a companion star with a long-period orbit deflecting other bodies from their normal orbits, making some of them fall to Earth as meteors and causing wide
29、spread devastation upon impact. 6. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. Based on their studies of extinction rates of numerous fossi
30、l groups, paleontologists David Raup and John Sepkoski have determined that mass extinctions occur about every 26 million years. David Raup and John Sepkoski studied extinction rates of numerous fossil groups and suggest that mass extinctions during the Cretaceous period continued for 26 million yea
31、rs. Studies that paleontologists David Raup and John Sepkoski conducted of various fossil groups have revealed that extinction rates have increased over the past 26 million years. The studies conducted by paleontologists David Raup and John Sepkoski of the fossil remains of species suggest that the
32、extinction rate of species started to increase by the middle of the Cretaceous period. 7. According to paragraph 4, what aspect of extinction episodes does the companion- star hypothesis supposedly clarify? Their location Their frequency Their duration Their severity Paragraph 5: Of the various hypo
33、theses attempting to account for the late Cretaceous extinctions, the one that has attracted the most attention in recent years is the asteroid-impact hypothesis first suggested by Luis and Walter Alvarez. According to this hypothesis, Earth collided with an asteroid with an estimated diameter of 10
34、 kilometers, or with several asteroids, the combined mass of which was comparable. The force of collision spewed large amounts of debris into the atmosphere, darkening the skies for several years before the finer particles settled. The reduced level of photosynthesis led to a massive decline in plan
35、t life of all kinds, and this caused massive starvation first of herbivores and subsequently of carnivores. The mass extinction would have occurred very suddenly under this hypothesis. 8. The phrase account for in the passage is closest in meaning to describe challenge explain test Paragraph 6: One
36、interesting test of the Alvarez hypothesis is based on the presence of the rare-earth element iridium (Ir). Earths crust contains very little of this element, but most asteroids contain a lot more. Debris thrown into the atmosphere by an asteroid collision would presumably contain large amounts of i
37、ridium, and atmospheric currents would carry this material all over the globe. A search of sedimentary deposits that span the boundary between the Cretaceous and Tertiary periods shows that there is a dramatic increase in the abundance of iridium briefly and precisely at this boundary. This iridium
38、anomaly offers strong support for the Alvarez hypothesis even though no asteroid itself has ever been recovered. 9. According to paragraph 6, what made iridium a useful test of the Alvarez hypothesis? Its occurrence in a few locations on Earth against several locations on other planets Its occurrenc
39、e in limited quantities on Earth against its abundance in asteroids Its ability to remain solid at extremely high temperatures Its ease of detection even in very small amounts 10. In stating that no asteroid itself has ever been recovered, the author emphasizes which of the following? The importance
40、 of the indirect evidence for a large asteroid The fact that no evidence supports the asteroid?impact hypothesis The reason many researchers reject the Alvarez hypothesis The responsibility of scientists for not making the effort to discover the asteroid itself Paragraph 7: An asteroid of this size
41、would be expected to leave an immense crater, even if the asteroid itself was disintegrated by the impact. The intense heat of the impact would produce heat-shocked quartz in many types of rock. Also, large blocks thrown aside by the impact would form secondary craters surrounding the main crater. T
42、o date, several such secondary craters have been found along Mexicos Yucatan Peninsula, and heat-shocked quartz has been found both in Mexico and in Haiti. A location called Chicxulub, along the Yucatan coast, has been suggested as the primary impact site. 11. The word intense in the passage is clos
43、est in meaning to sudden unusual immediate extreme 12. What is the purpose of paragraph 7 in the passage? It proposes a decisive new test of the Alvarez hypothesis. It presents additional supporting evidence for the Alvarez hypothesis. It explains why evidence relating to the Alvarez hypothesis is h
44、ard to find. It shows how recent evidence has raised doubts about the Alvarez hypothesis. Paragraph 1: Cases in which many species become extinct within a geologically short interval of time are called mass extinctions. There was one such event at the end of the Cretaceous period (around 70 million
45、years ago). There was another, even larger, mass extinction at the end of the Permian period (around 250 million years ago). The Permian event has attracted much less attention than other mass extinctions because mostly unfamiliar species perished at that time. 13. Look at the four squares that indi
46、cate where the following sentence could be added to the passage. In general, it is believed that these two extinctions resulted from drastic environmental changes that followed meteorite impacts or massive volcanic eruptions. Where would the sentence best fit? 14. Directions: An introductory sentenc
47、e 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 ideas that are not presented in the passage or are minor ideas in
48、the passage. This question is worth 2 points. There have been many attempts to explain the causes of mass extinctions. Answer Choices Asteroid impacts, evolutionary developments, and changes in Earths climate and in the positions of the continents have all been proposed as possible causes of mass extinctions