GMAT阅读机经整理：冰期理论.

　　3月2日换库后，小编为大家整理这个月的GMAT阅读机经，这篇GMAT阅读机经是关于冰期理论的文章，考生朋友可以看看，下面的内容为考古内容，分享给大家，希望对大家有所帮助，文中观点仅供参考。

　　[V1]

　　一个讲的是一个人的一个理论，说是最开始挺权威的大家都信，后来发现证据说他不对，后来又发现其实他是对的

　　[V2]

　　还有一篇把LZ吓傻了，还以为粗事了： OG13上米兰科维奇的冰期理论。。。回来发现OG上的文章只是提了M一下，不一样。没怎么读秒选的。

　　第一段大概介绍了M说的variations in the Earth&aposs orbit around the sun会导致的后果，比如冰期之类的。还有其他内容，没有读。第二段分两部分吧大概，先是说50年代随着碳14测定技术等的发展，科学家们陆续从调查中发现，M算的冰期时间与测算出来的不符，于是大家纷纷唾弃他。接着，随着科学技术的进一步精确，科学家们重新测算的冰期与Milankovitch cycle是相符的，于是大家纷纷开始赞成他。。。

　　题目有一道是：如果50年代的测算结果是正确的，那么会发生什么?(推断)

　　答案当然是科学家们那个时候就会赞成M了。。。 别的题目忘了，选的比较快

　　[V3]

　　好长的一篇，是说间冰期那个时候的冰的移动还是神马的，最后一篇，时间不够没细看，一共是两段，而且是灰常长的两端，整篇文章有一屏半，第一段就是说1920s那个时候的理论说神马神马，然后第二段however 开头，明显的反驳了这个理论，提出了1950s那个时候的啥啥啥人的理论观点，然后有个题是这个1950年的theory处高亮了，后面还有1970s的神马人又提出了数据support1950s的这个观点，这里有题就是说这个1970s的数据是什么作用的，文章的总体结构很清晰，但是又长又臭，我也没时间细看，原谅我，不过我总觉得这篇文章在哪见过~~~~~~~

　　[V4]

　　说从岩石来测算有多少年历史的，2段，第一段说1920s,一个科学家有一种方法，解释了一遍，不难看懂。第二段，开头一个词就是BUT,提出1950s的时候一些科学家就有新方法，觉得之前这个人的是错的，不是那么测得，然后紧接着又转折，说后来过了些年，科技发达了，有个很精确的方法可以坚定了，直接把1950那种方法给否了，说人们又觉得1920的科学家提出来的是acceptable的。

　　考古已确认

　　V1

　　先是陈述了这个理论 然后说当时人们只能在实验条件不足的情况下 大体的承认这个理论。但是1950年出了个A.B 研究了一些东西 carbon rating之类的，说是理论错误了。(我觉得这段时间内人们都不再接受M的理论了.随着科技的进步,应该是旧的改良结合很多其它新的technology出现了，证明了AB的 证据索取是比较片面的 M再次被人们接受。

　　问题：

　　1. A..B. 对MilankovitchCycles Theory的看法导致一段时间内人们都不再接受M的理论了

　　2. 主题题：选的不同的方法对某一科学推断的研究和看法(没有一个选项提到了Milankovitch CyclesTheory,所以猜测某一科学推断指代Milankovitch CyclesTheory)。

　　3.Infer: 说如果第一段那些“当时人们”有accurate carbondating technologies 的时候，他们会怎样?

　　4. 新的学者(高亮了)对MilankovitchCycles Theory的看法

　　V2

　　某教授在1920S研究发现冰河期和地球轨道有关，然后是通过化石做了张表来说明。第二段突然说1950S科技进不了，发觉他理论不对了。然后1980S，科技有进步了，说其实1950S是不对的，以前那个教授其实是对的。

　　V3

　　P1：该理论的贡献

　　P2：该理论受到新的基于quantative和radiocarbon方法的挑战，被数据证实有误，但后来的研究证明上述方法有问题，新的更精确的方法验证了M理论的正确性，因而M理论重新得到认可

　　问题：1。 如果基于quantative和radiocarbon方法得到的结果是正确的，那会有什么结果。(答案都忘了，但此题不易解，干扰项严重)

　　V4

　　是change in earth orbit. 第一段讲M的理论多牛B，第二段讲50年代的什么试验证明M是错的，然后第二段的后半部分又说原来50年代的试验方法(还是数据?)是错误的，这样的话M的理论又被证明是对的了。

　　V5

　　然后还有一篇很长很长的是讲冰川的.第一段基本不考(大家大概扫扫好了,这文章有一屏半), 全是highlight的第二段.大意就是有一个专家提出了一个理论研究冰川的layer可以计算出时间还是什么的.第二段有人提出质疑,通过什么新的技术证明专家说的不对(有一个题目提到highlight的theorist起什么作用),但是1970年又有人重新做了research,发现其实质疑是错误的,于是还专家一个清白(有一道题目就是问1970年的研究做什么了,我觉得貌似应该是revise专家的提议).还有主旨题目.

　　V6

　　第一段：1920年，一个科学家M.M.(首字母)提出一个Claim/Theory说貌似地球的Orbit和Ice Age有关系。他的证据是在一些(可能是南北极的)冰川Layer里面发现了一些植物的标本。。

　　第二段：但是到了1950年，有一个根据CO2的研究指出M.M.的理论有问题，貌似指出问题的关键也是植物的标本问题。后来1970年研究技术更新之后，通过新技术表明，M.M.的理论还是可以被接受的~

　　V7

　　说M发现通过什么东西可以考证冰川的年代 而且这个东西受地球自转的影响。而且冰川会在世界各地周期性出现(澳大利亚除外，这里看似重要，但是没考) 后来第二段有科学家用新的 carbon dating技术推翻了他的结论，很多细节，完全没看懂，最后1970年以后一个什么技术的出现又还了M一个清白

　　V8

　　有一篇讲一个地质学家发现地球轨道会影响地球的气候，会使气候变冷，这个理论可以解释很多历史现象。但是1950年代的地质学家们发现用C测量一些化石的年龄，发现和上述理论相矛盾，说明上述理论错了，但1970年的地质学家们又发现1950年的测量不准确，那个理论是对的

　　注：在OG11和OG12中都有一篇阅读是关于Milankovitch理论的，但是并非此月的阅读原文，大家可以当背景资料阅读，我提供文章的开头关键句供大家查找：Milankovitch proposed in the early twentieth century that the ice ages were caused by variations in the Earth’s orbit around the Sun. 另外，看看下面的背景资料会对阅读有所帮助。

　　Milankovitch Cycles Theory

　　Milankovitch cycles theory is about the frequency of ice age. Milankovich proposed that the temperature of earth has something to do with the position of the earth in the orbit around sun. However it did not gain acceptance until 1968 when Dr. Imbrie presented additional evidence for M theory. He meassured the isotope level in small seashell deposit and the change of isotope abundancy corresponds with the temperature change.

　　However, later on, a geochemist tested the samples from Devil&aposs Hole, a place in south Nevada and the results did not match with the previous results.

　　Even thought Dr. Imbrie still think M theory was valid, he conceded that many other factors contribute to the isotope level. It maybe why the results did not match.

　　OLD JJ

　　V1

　　是讲某人MM的理论，关于change in earth‘s orbit影响气候什么的，也没看懂……

　　V2

　　03/21 第二篇是change in earth orbit. 第一段讲M的理论多牛B，第二段讲50年代的什么试验证明M是错的，然后第二段的后半部分又说原来50年代的试验方法(还是数据?)是错误的，这样的话M的理论又被证明是对的了。

　　有益补充1：地球轨道根数变化与第四纪冰期 Changes of the Earth&aposs Orbital Elements and the Quaternary Glacial Epoch

　　米兰柯维奇(Milankovitch)天文气候学理论和第四纪地质时期以来冰期的研究进展.研究结果表明,地球上的冰体积具有近10万yr的变化周期,并伴有近4万yr和2万yr的变化周期,它们是由于地球的轨道根数变化导致的气候变迁所致;不同的地球物理资料中均存在上述类似的变化周期,表明气候变迁所导致的变化是全球性效应,证实米兰柯维奇天文理论是基本正确的。这个像不像jj里讲的mm理论? 冰川变化 地球轨道

　　有益补充2 (补充1的英文)：

　　At the recent American Geophysical Union meeting in San Francisco, the 25th anniversary of one of the great

　　papers in paleoclimatology was celebrated. The paper, entitled “Variations in the Earth’s orbit: Pacemaker

　　of the Ice Ages,” presented important new evidence supporting the orbital theory of glaciation. Orbital theory goes back over a century but is most closely associated with Milankovitch, who calculated the fects of gravitational perturbations on the seasonal cycle of Earth’s insolation (the radiation incident at the top of the atmosphere). Insolation varies on several time scales, including ~20,000 years (termed precession), ~40,000.

　　参考阅读

　　Can We Date the Ice Ages?

　　Following improvements in the ability to measure isotope ratios which came about as a spin-off of the wartime Manhattan project, physical chemist Harold Urey began to examine the possibility that the ratio of the two principal isotopes of oxygen found in the atmosphere might provide a clue as to past temperatures. It was based on the idea that the ratio of the heavier isotope (oxygen-18) to the more prevalent isotope (oxygen-16) found at the sea surface would change depending on the temperature of the ocean water near the surface. Urey thought that a carul study of the oxygen isotope ratio in the shells of sea creatures, which build their calcium carbonate shells from oxygen available in the seawater, might serve to indicate the temperature of the water in which they formed. During warmer periods, it was thought, evaporation from the ocean surface would tend to enrich the sea surface water with the heavier isotope of oxygen.

　　Perhaps, Urey reasoned, the isotope ratios found in the layers of discarded shells of sea organism which form the ocean bottom could thus serve as a record for the past temperatures of the ocean.

　　The theory is fraught with many ifs, but it was pursued with persistence, starting in the 1950s, by Italian-educated micropaleontologist Cesare Emiliani, a one-time collaboator of Urey at the Argonne Laboratory then associated with University of Chicago. Emiliani identified certain species of small shell-forming sea organisms known as foraminifera, which he thought suitable for oxygen-isotope analysis to determine past climates. The conclusions he drew as to the dating of the ice ages were constantly challenged by leading oceanographers, who found them in contradiction with their studies of ocean bottom cores. The method was also attacked on the grounds that it wasn&apost clear that the creatures formed their shells, known as tests, near enough to the surface to rlect changes in isotope ratios.

　　About 1968, a somewhat new interpretation of the oxygen isotope record was proposed by a young oceanographer and climatologist, Nicholas Shackleton, a Cambridge graduate and great nephew of the famous British Antarctic explorer of the same name. Shackleton proposed that the oxygen-isotope ratio could serve as a proxy, not for temperature but for sea level--the idea being that during periods of glacial advance, when a large volume of ocean water had been taken up into the continental ice sheets, the oxygen-18 ratios of the remaining water would consequently be higher. These might be detected in the foraminifera layers found in the ocean bottom cores. Again there are many ifs, but Shackleton examined isotopic ratios of snows in Alpine and Arctic regions as well as many other factors to bolster his hypothesis. In the 1970s a National Science Foundation-funded program of oceanographic studies, known as CLIMAP, collected a large number of sediment cores from different parts of the world ocean. The program, known as the Decade of the Oceans, was run in conjunction with some flawed statistical approaches to modeling of global atmospheric circulation that had originated in forts of John von Neumann to use computer modeling for studies of weather modification. However, analysis of the oxygen isotopic ratios of foraminifera found in the undersea cores suggested to a team working at the Lamont-Doherty Geological Laboratory that there was a dinite signal of 100,000 year cyclicity. Dr. John Imbrie, who ran the computer programs analyzing the data, was the first to hypothesize that the periodicities were caused by the Milankovitch orbital cycles.

　　A landmark paper by Hays, Imbrie and Shackleton, published in the December 1976 issue of Science magazine ("Variations in the Earth&aposs Orbit: Pacemaker of the Ice Ages"), argued that the advance and retreat of the ice sheets was triggered by the changes in the Earth&aposs orbital parameters. Other factors might also be present to reinforce these relatively small changes in solar radiation, but these were the pacemaker. By the theory of the orbital cycles, the evidence from the undersea cores explained that a major glaciation would be set off about every 100,000 years, followed by a short period known as an interglacial, a melt back lasting about 10,000 to 12,000 years. By the calculations of astronomers, the present interglacial, which has lasted about 11,000 years, is due to end any time. Indeed we have been in a period of long-term cooling for more than 6,000 years. The maximum summer temperature experienced in Europe over the last 10,000 years occurred about 6000 B.C. Over North America, where the process of glacial retreat lagged somewhat, the maximum was reached by about 4000 B.C. These estimates based on a vast array of evidence from geology, botany, and many other fields are consistent with the orbital theory of climate, for the northern hemisphere Summer would have been occurring at a point in Earth&aposs orbit much nearer to the Sun than presently.

　　"One of the fundamental tenets of palaeoclimate modeling, the Milankovitch theory, is called into doubt by isotope analysis of a calcite vein, just reported in Science by Winograd and colleagues. The theory, which is backed up by a compelling bank of evidence, suggests that the ice ages determined, with unprecedented accuracy, in the new record cannot be reconciled with the planetary cyclicity. . .

　　Winograd and colleagues&apos evidence also turns on oxygen isotope data, this time from vein calcite coating the hanging wall of an extensional fault at Devils Hole, an aquifer in southern Nevada. In 1988, the authors published a date, 145,000 years, based on 234U-230Th dating for the end of the penultimate ice age (Termination II), marked by an increase in the 18O to 16O ratio, a change taken to mirror an increase in local precipitation. Although the date was only 17,000 year earlier than the previously accepted date of 128,000 years, if correct, this change is enough to bring Milankovitch mechanism into serious doubt. . .

　　I remain confused. The geochemist in me says that Devils Hole chronology is the best we have. And the palaeoclimatologist in me says that correlation between accepted marine chronology and Milankovitch cycles is just too convincing to be put aside. . .

　　One side will have to give, and maybe - just to be safe - climate modellers should start preparing themselves for a world without Milankovitch."

　　以上就是关于冰期理论这篇GMAT阅读机经的全部内容，考生可以有选择的看看，机经虽好，但是也要适度哟。最后祝大家都能考出好成绩。