标题: Milankovitch Cycles Theory背景知识~~~ [打印本页] 作者: shihui0012 时间: 2009-12-8 22:11 标题: Milankovitch Cycles Theory背景知识~~~ Most scientists believe that the ice ages are the result of subtle changes in Earth's orbit, known as the Milankovitch cycles. One such cycle describes the way Earth's orbit gradually changes shape from a circle to a slight ellipse and back again roughly every 100,000 years. The theory says this alters the amount of solar radiation that Earth receives, triggering the ice ages. However, a persistent problem with this theory has been its inability to explain why the ice ages changed frequency a million years ago.
7 "In Milankovitch, there is certainly no good idea why the frequency should change from one to another," says Neil Edwards, a climatologist at the Open University in Milton Keynes, UK. Nor is the transition problem the only one the Milankovitch theory faces. Ehrlich and other critics claim that the temperature variations caused by Milankovitch cycles are simply not big enough to drive ice ages.
8 However, Edwards believes the small changes in solar heating produced by Milankovitch cycles are then amplified by feedback mechanisms on Earth. For example, if sea ice begins to form because of a slight cooling, carbon dioxide that would otherwise have found its way into the atmosphere as part of the carbon cycle is locked into the ice. That weakens the greenhouse effect and Earth grows even colder.
9 According to Edwards, there is no lack of such mechanisms. "If you add their effects together, there is more than enough feedback to make Milankovitch work," he says. "The problem now is identifying which mechanisms are at work." This is why scientists like Edwards are not yet ready to give up on the current theory. "Milankovitch cycles give us ice ages roughly when we observe them to happen. We can calculate where we are in the cycle and compare it with observation," he says. "I can't see any way of testing [Ehrlich's] idea to see where we are in the temperature oscillation."
10 Ehrlich concedes this. "If there is a way to test this theory on the sun, I can't think of one that is practical," he says. That's because variation over 41,000 to 100,000 years is too gradual to be observed. However, there may be a way to test it in other stars: red dwarfs. Their cores are much smaller than that of the sun, and so Ehrlich believes that the oscillation periods could be short enough to be observed. He has yet to calculate the precise period or the extent of variation in brightness to be expected.
11 Nigel Weiss, a solar physicist at the University of Cambridge, is far from convinced. He describes Ehrlich's claims as "utterly implausible". Ehrlich counters that Weiss's opinion is based on the standard solar model, which fails to take into account the magnetic instabilities that cause the temperature fluctuations. 米兰科维奇理论认为，北半球高纬夏季太阳辐射变化是驱动第四纪冰期旋回的主因。这个理论的核心是单一敏感区的触发驱动机制，即北半球高纬气候变化信号被放大、传输进而影响全球。最近，由于大量高分辨率及精确定年的气候变化记录的获得，从以下4个方面构成了对米氏理论的挑战：1）一些低纬地区并没有明显的10万年冰量周期，而是以2万年岁差周期为主，表明北半球冰盖的扩张、收缩变化并没有完全控制低纬区的气候变化；2）在最近几次冰消期时，南半球和低纬区的温度增高，要早于北半球冰盖的融化，表明冰消期的触发机制并非是北半球高纬夏季太阳辐射；3）大气CO2浓度在第2冰消期的增加同南极升温相一致，表明该时大气CO2浓度增加亦有可能早于北半球冰盖消融；4）南半球的末次冰盛期有可能早于北半球。这就说明单一敏感区触发驱动机制已难以圆满解释所有观察事实，天文因素控制下轨道尺度气候变化机制研究正面临理论突破的新需求和新机遇
Milankovitch proposed in the early twentieth century that the ice ages were caused by variations in the Earth’s orbit around the Sun. For some time this theory was considered untestable, (5)largely because there was no sufficiently precise chronology of the ice ages with which the orbital variations could be matched. 1：M提出一个理论, 指出其缺陷 To establish such a chronology it is necessary to determine the relative amounts of land ice that (10)existed at various times in the Earth’s past. A recent discovery makes such a determination possible: relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments. Almost (15)all the oxygen in water is oxygen 16, but a few molecules out of every thousand incorporate the heavier isotope 18. When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that (20)will eventually return to it. Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18. The degree of enrichment can be determined (25)by analyzing ocean sediments of the period, because these sediments are composed of calcium carbonate (calcium carbonate: n.[化]碳酸钙) shells of marine organisms, shells that were constructed with oxygen atoms drawn from the surrounding ocean. The higher the ratio of (30)oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down. 2: 一个新发现可弥补M理论的缺陷 As an indicator of shifts in the Earth’s climate, the isotope record has two advantages. First, it is (35)a global record: there is remarkably little variation in isotope ratios in sedimentary specimens taken from different continental locations. Second, it is a more continuous record than that taken from rocks on land. Because of these advantages, (40)sedimentary evidence can be dated with sufficient accuracy by radiometric methods to establish a precise chronology of the ice ages. The dated isotope record shows that the fluctuations in global ice volume over the past several hundred (45)thousand years have a pattern: an ice age occurs roughly once every 100,000 years. These data have established a strong connection between variations in the Earth’s orbit and the periodicity of the ice ages. 3：新发现的优点 However, it is important to note that other (50)factors, such as volcanic particulates or variations in the amount of sunlight received by the Earth, could potentially have affected the climate. The advantage of the Milankovitch theory is that it is testable: changes in the Earth’s orbit can be (55)calculated and dated by applying Newton’s laws of gravity to progressively earlier configurations of the bodies in the solar system. Yet the lack of information about other possible factors affecting global climate does not make them unimportant. 4：其他的理论也不容忽视 70. In the passage, the author is primarily interested in 主题题（D） suggesting an alternative to an outdated research method introducing a new research method that calls an accepted theory into question emphasizing the instability of data gathered from the application of a new scientific method presenting a theory and describing a new method to test that theory（D） initiating a debate about a widely accepted theory
71. The author of the passage would be most likely to agree with which of the following statements about the Milankovitch theory? 应用题（D） It is the only possible explanation for the ice ages. It is too limited to provide a plausible explanation for the ice ages, despite recent research findings. It cannot be tested and confirmed until further research on volcanic activity is done. It is one plausible explanation, though not the only one, for the ice ages. （D） It is not a plausible explanation for the ice ages, although it has opened up promising possibilities for future research.
72. It can be inferred from the passage that the isotope record taken from ocean sediments would be less useful to researchers if which of the following were true? 推导题（B） the isotope record has two advantages. First, it is (35)a global record；Second, it is a more continuous record than that taken from rocks on land It indicated that lighter isotopes of oxygen predominated at certain times. It had far more gaps in its sequence than the record taken from rocks on land.否定了第二点 It indicated that climate shifts did not occur every 100,000 years.削弱M理论，而不是方法 It indicated that the ratios of oxygen 16 and oxygen 18 in ocean water were not consistent with those found in fresh water. （B） It stretched back for only a million years.
73. According to the passage, which of the following is true of the ratios of oxygen isotopes in ocean sediments? 观点题（C） relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments. They indicate that sediments found during an ice age contain more calcium carbonate than sediments formed at other times. They are less reliable than the evidence from rocks on land in determining the volume of land ice. They can be used to deduce the relative volume of land ice that was present when the sediment was laid down. They are more unpredictable during an ice age than in other climatic conditions. （C） They can be used to determine atmospheric conditions at various times in the past.
74. It can be inferred from the passage that precipitation formed from evaporated ocean water has 推导题（B） Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18. the same isotopic ratio as ocean water less oxygen 18 than does ocean water less oxygen 18 than has the ice contained in continental ice sheets a different isotopic composition than has precipitation formed from water on land（B） more oxygen 16 than has precipitation formed from fresh water
75. It can be inferred from the passage that calcium carbonate shells 推导题（D） shells that were constructed with oxygen atoms drawn from the surrounding ocean. are not as susceptible to deterioration as rocks are less common in sediments formed during an ice age are found only in areas that were once covered by land ice contain radioactive material that can be used to determine a sediment’s isotopic composition reflect the isotopic composition of the water at the time the shells were formed作者: delan714 时间: 2009-12-8 23:07
这篇是雅思上的，大家随便看看好了
From New Scientist Print Edition. Stuart Clark 1 There's a dimmer switch inside the sun that causes its brightness to rise and fall on timescales of around 100,000 years - exactly the same period as between ice ages on Earth. So says a physicist who has created a computer model of our star's core. 2 Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled the effect of temperature fluctuations in the sun's interior. According to the standard view, the temperature of the sun's core is held constant by the opposing pressures of gravity and nuclear fusion. However, Ehrlich believed that slight variations should be possible. 3 He took as his starting point the work of Attila Grandpierre of the Konkoly Observatory of the Hungarian Academy of Sciences. In 2005, Grandpierre and a collaborator, Gábor ágoston, calculated that magnetic fields in the sun's core could produce small instabilities in the solar plasma. These instabilities would induce localised oscillations in temperature. 4 Ehrlich's model shows that whilst most of these oscillations cancel each other out, some reinforce one another and become long-lived temperature variations. The favoured frequencies allow the sun's core temperature to oscillate around its average temperature of 13.6 million kelvin in cycles lasting either 100,000 or 41,000 years. Ehrlich says that random interactions within the sun's magnetic field could flip the fluctuations from one cycle length to the other. 5 These two timescales are instantly recognisable to anyone familiar with Earth's ice ages: for the past million years, ice ages have occurred roughly every 100,000 years. Before that, they occurred roughly every 41,000 years. 6 Most scientists believe that the ice ages are the result of subtle changes in Earth's orbit, known as the Milankovitch cycles. One such cycle describes the way Earth's orbit gradually changes shape from a circle to a slight ellipse and back again roughly every 100,000 years. The theory says this alters the amount of solar radiation that Earth receives, triggering the ice ages. However, a persistent problem with this theory has been its inability to explain why the ice ages changed frequency a million years ago. 7 "In Milankovitch, there is certainly no good idea why the frequency should change from one to another," says Neil Edwards, a climatologist at the Open University in Milton Keynes, UK. Nor is the transition problem the only one the Milankovitch theory faces. Ehrlich and other critics claim that the temperature variations caused by Milankovitch cycles are simply not big enough to drive ice ages. 8 However, Edwards believes the small changes in solar heating produced by Milankovitch cycles are then amplified by feedback mechanisms on Earth. For example, if sea ice begins to form because of a slight cooling, carbon dioxide that would otherwise have found its way into the atmosphere as part of the carbon cycle is locked into the ice. That weakens the greenhouse effect and Earth grows even colder. 9 According to Edwards, there is no lack of such mechanisms. "If you add their effects together, there is more than enough feedback to make Milankovitch work," he says. "The problem now is identifying which mechanisms are at work." This is why scientists like Edwards are not yet ready to give up on the current theory. "Milankovitch cycles give us ice ages roughly when we observe them to happen. We can calculate where we are in the cycle and compare it with observation," he says. "I can't see any way of testing [Ehrlich's] idea to see where we are in the temperature oscillation." 10 Ehrlich concedes this. "If there is a way to test this theory on the sun, I can't think of one that is practical," he says. That's because variation over 41,000 to 100,000 years is too gradual to be observed. However, there may be a way to test it in other stars: red dwarfs. Their cores are much smaller than that of the sun, and so Ehrlich believes that the oscillation periods could be short enough to be observed. He has yet to calculate the precise period or the extent of variation in brightness to be expected. 11 Nigel Weiss, a solar physicist at the University of Cambridge, is far from convinced. He describes Ehrlich's claims as "utterly implausible". Ehrlich counters that Weiss's opinion is based on the standard solar model, which fails to take into account the magnetic instabilities that cause the temperature fluctuations. (716 words) Questions 1-4 Complete each of the following statements with One or Two names of the scientists from the box below. Write the appropriate letters A-E in boxes 1-4 on your answer sheet. A. Attila Grandpierre B. Gábor ágoston C. Neil Edwards D. Nigel Weiss E. Robert Ehrlich 1. ...claims there抯 a dimmer switch inside the sun that causes its brightness to rise and fall in periods as long as those between ice ages on Earth. 2. ...calculated that the internal solar magnetic fields could produce instabilities in the solar plasma. 3. ...holds that Milankovitch cycles can induce changes in solar heating on Earth and the changes are amplified on Earth. 4. ...doesn't believe in Ehrlich's viewpoints at all. Questions 5-9 Do the following statements agree with the information given in the reading passage? In boxes 5-9 on your answer sheet write TRUE if the statement is true according to the passage FALSE if the statement is false according to the passage NOT GIVEN if the information is not given in the passage 5. The ice ages changed frequency from 100,000 to 41,000 years a million years ago. 6. The sole problem that the Milankovitch theory can not solve is to explain why the ice age frequency should shift from one to another. 7. Carbon dioxide can be locked artificially into sea ice to eliminate the greenhouse effect. 8. Some scientists are not ready to give up the Milankovitch theory though they haven't figured out which mechanisms amplify the changes in solar heating. 9. Both Edwards and Ehrlich believe that there is no practical way to test when the solar temperature oscillation begins and when ends.
Questions 10-14 Complete the notes below. Choose one suitable word from the Reading Passage above for each answer. Write your answers in boxes 10-14 on your answer sheet. The standard view assumes that the opposing pressures of gravity and nuclear fusions hold the temperature ...10...in the sun's interior, but the slight changes in the earth's ...11... alter the temperature on the earth and cause ice ages every 100,000 years. A British scientist, however, challenges this view by claiming that the internal solar magnetic ...12... can induce the temperature oscillations in the sun's interior. The sun's core temperature oscillates around its average temperature in ...13... lasting either 100,000 or 41,000 years. And the ...14... interactions within the sun's magnetic field could flip the fluctuations from one cycle length to the other, which explains why the ice ages changed frequency a million years ago. Answer keys and explanations: 1. E See the sentences in paragraph 1(There's a dimmer switch inside the sun that causes its brightness to rise and fall on timescales of around 100,000 years - exactly the same period as between ice ages on Earth. So says a physicist who has created a computer model of our star's core.) and para.2 (Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled the effect of temperature fluctuations in the sun's interior.) 2. A B See para.3: ?i style='mso-bidi-font-style: normal'>Grandpierre and a collaborator, Gábor ágoston, calculated that magnetic fields in the sun's core could produce small instabilities in the solar plasma. 3. C See para.8: Edwards believes the small changes in solar heating produced by Milankovitch cycles are then amplified by feedback mechanisms on Earth. 4. D See para.11: Nigel Weiss, a solar physicist at the University of Cambridge, is far from convinced. He describes Ehrlich's claims as "utterly implausible". 5. False See para.5: for the past million years, ice ages have occurred roughly every 100,000 years. Before that, they occurred roughly every 41,000 years. 6. False See para.7: "In Milankovitch, there is certainly no good idea why the frequency should change from one to another," ... Nor is the transition problem the only one the Milankovitch theory faces. 7. Not Given See para.8: if sea ice begins to form because of a slight cooling, carbon dioxide?is locked into the ice. That weakens the greenhouse effect. (The passage doesn抰 mention anything about locking Co2 into ice artificially.) 8. True See para.9: there is no lack of such mechanisms. "If you add their effects together, there is more than enough feedback to make Milankovitch work,"?"The problem now is identifying which mechanisms are at work." This is why scientists like Edwards are not yet ready to give up on the current theory. 9. True See the sentences in para.9 (According to Edwards, 卙e says. "I can't see any way of testing [Ehrlich's] idea to see where we are in the temperature oscillation.") and para.10 (Ehrlich concedes this. "If there is a way to test this theory on the sun, I can't think of one that is practical). 10. constant See para.2: According to the standard view, the temperature of the sun's core is held constant by the opposing pressures of gravity and nuclear fusion. 11. orbit See para.6: Most scientists believe that the ice ages are the result of subtle changes in Earth's orbit, 匛arth's orbit gradually changes shape from a circle to a slight ellipse and back again roughly every 100,000 years. 12. instabilities See para.3: ?i style='mso-bidi-font-style:normal'>magnetic fields in the sun's core could produce small instabilities in the solar plasma. These instabilities would induce localised oscillations in temperature. 13. cycles See para.4: …allow the sun's core temperature to oscillate around its average temperature of 13.6 million kelvin in cycles lasting either 100,000 or 41,000 years. 14. random See para.4: Ehrlich says that random interactions within the sun's magnetic field could flip the fluctuations from one cycle length to the other.作者: dxm0929 时间: 2009-12-10 22:14
1：M提出一个理论, 指出其缺陷