GMAT閱讀機(jī)經(jīng)整理：月球形成的三種學(xué)說.

　　4月5日GMAT換庫后，小編為大家收集整理4月份的GMAT閱讀機(jī)經(jīng)，這篇是關(guān)于月球形成的三種學(xué)說的文章，分享給大家，希望對大家有所幫助，僅供參考。

　　一、本月原始

　　月亮是怎么形成的。先提出三種理論：1. Moon formed from a part of the earth 2. The moon and the earth formed independently of each other, at the same time 3.The moon was‘captured’ by the earth’s gravitational pull。作者提出一些證據(jù)，說明這三種理論都是不太可能的。最后一段說了第四種理論：月亮是什么東西和地球碰撞后產(chǎn)生的，并且提供證據(jù)，說明這個最有可能

　　二、主旨

　　三種學(xué)說。拿出證據(jù)全部否定(全是細(xì)節(jié)題)。新的學(xué)說。

　　三、文章結(jié)構(gòu)

　　? 文章(舊的假說—混合反駁—新的解釋)

　　四、 段落大意

　　P1：早在Apollo登月之前，就對月球的形成有三種學(xué)說：

　　(1)分裂說fission：地球甩出去的

　　(2)同源說concurrence：和地球一起形成的，此理論成立的話月亮和地球應(yīng)該有同樣的materials

　　(3)俘獲說capture：獨立形成

　　P2： 登月后采集了樣本數(shù)據(jù)和研究成果，發(fā)現(xiàn)三種說法都錯：分別給出理由【運動和組成成分的證據(jù)】。

　　(1) 首先否定fission，月亮如果是地球分離出去的話，那么地月系統(tǒng)轉(zhuǎn)的速度都要比現(xiàn)在快(in fission model earth and moon have much more spin)。

　　crater應(yīng)該很厚。但是……：反分裂;

　　現(xiàn)在的地月系統(tǒng)應(yīng)該轉(zhuǎn)得更快(spin)。但是……：反分裂;(Q2)

　　應(yīng)該還有很多小的衛(wèi)星體在地球周圍。但是……：反分裂;

　　如果是capture，月亮這個獨立的星體應(yīng)該運動的很慢，才會落入地系，反capture;(Q3)

　　(2)提出一個證據(jù)，發(fā)現(xiàn)月球與地球的materials不同。如果是concurrence，月球應(yīng)該具有和地球類似的組成(materials)，但是發(fā)現(xiàn)月球上的活潑金屬(volatile mental)，比如zinc，lead的含量比地球少很多。反fission、concurrence;

　　(3) 最后提出一個證據(jù)，說是月球的core size很小,和地球不像。月球的鐵內(nèi)核(iron)應(yīng)該跟地球相似，所以應(yīng)該比現(xiàn)在的更大。因此不可能是獨立的小星星，也不可能是concurrence的，否定了capture和concurrence。 (Q4) (Q5)

　　P3：提出新理論：collision學(xué)說，合理的解釋了一切之前的不合理。

　　(1)活潑金屬少：因為地球和另一個宇宙中的物體擦肩而過，溫度高而揮發(fā);

　　(2)core?。阂驗樽财?

　　(3)轉(zhuǎn)速：因為有角度撞擊，所以變慢了。

　　五、題目

　　Q1. 主旨/結(jié)構(gòu)

　　提出了幾個存在問題的理論最后提出了一個較完美的理論。

　　Q2. 如果fission成立的話月球會是什么樣子? /if the fission(分裂學(xué)說) model is true, the moon that differ the current is 。。(就是如果fission是正確的，月亮?xí)c現(xiàn)在的有什么不同。)

　　A. Spin faster than now

　　B. Spin slower

　　C. 月亮周圍會有很多Material.

　　狗主解釋：幾經(jīng)上說是spin faster or slower. 當(dāng)時做題的時候出現(xiàn)了spin slower，但是回文中定位發(fā)現(xiàn)in fission model earth and moon have much more spin. 就是說要快，所以這個不對，我選擇的是月亮周圍會有很多Material.因為定為第一段說fission使地球甩出去很多物質(zhì)。

　　Q3. 如果俘獲論是正確的話，如何加強(qiáng)?

　　Spin slower than now

　　狗主解釋：就是找到第二段中的反對意見，改寫成否定就好了

　　Q4. 以下哪個為真，會削弱the objection to俘獲說capture?(注意!雙否定!)

　　對：月球的core其實比科學(xué)家預(yù)測的更大一些

　　(錯)科學(xué)家對月球表面元素的分析有錯誤;

　　(錯)月球crater的厚度被低估;

　　Q5. 如果月球是和地球同時形成的，會怎么樣?/哪個現(xiàn)象出現(xiàn)在同時形成這個學(xué)說中?/關(guān)于concurrence，一下那個觀點成立可以削弱科學(xué)家的結(jié)論?

　　the size of moon core 比科學(xué)家原來預(yù)測的大

　　六、小編分析:

　　如果fission成立：

　　l 現(xiàn)在的地月系統(tǒng)應(yīng)該轉(zhuǎn)得更快(much more spin)(考點)

　　l crater應(yīng)該很厚。

　　l 應(yīng)該還有很多小的衛(wèi)星體在地球周圍

　　l 它應(yīng)該具有和地球類似的組成(materials)(考點)

　　如果是capture：

　　l 月亮這個獨立的星體應(yīng)該運動的很慢(考點)

　　l 月球的core size比預(yù)測更大(考點)

　　如果是concurrence：

　　l 它應(yīng)該具有和地球類似的組成(materials)

　　l 月球的core size比預(yù)測更大(考點)

　　七、備注

　　注意第二段基本上是一對多的反駁，即一個證據(jù)同時反對多個理論。

　　新觀點沒有考點，全是針對錯誤解釋的改善題。

　　During the last two centuries, astronomers developed three different hypotheses for the origin of Earth’s moon, but these traditional ideas have failed to survive comparison with the evidence. A relatively new theory proposed in the 1970s may hold the answer. You can begin by testing the three unsuccessful theories against the evidence to see why they failed.

　　The first of the three traditional theories, the fission hypothesis, supposes that the moon formed by the fission of Earth. If the young Earth spun fast enough, tides raised by the sun might break into two parts. If this separation occurred after Earth differentiated, the moon would have formed from crust material, which would explain the moon’s low density. But the fission theory has problems. No one knows why the young Earth should have spun so fast, nearly ten times faster than today, nor where all that angular momentum went after the fission. In addition, the moon’s orbit is not in the plane of Earth’s equator, as it would be if it had formed by fission.

　　The second traditional theory is the condensation (or double-planet) hypothesis. It supposes that Earth and the moon condensed as a double planet from the same cloud of material. However, if they formed form the same material, they should have the same chemical composition and density, which they don’t. The moon is very poor in certain heavy elements like iron and titanium, and in volatiles such as water vapor and sodium. Yet the moon contains almost exactly the same rations of oxygen isotopes as does Earth’s mantle. The condensation theory cannot explain these compositional differences.

　　The third theory is the capture hypothesis. It supposes that the moon formed somewhere else and was later captured by Earth. If the moon formed inside the orbit of Mercury, the heat would have prevented the condensation of solid metallic grains, and only high-melting-point metal oxides could have solidified. According to the theory, a later encounter with Mercury could have “kicked” the moon out to Earth. The capture theory was never popular because it requires highly unlikely events involving interactions with Mercury and Earth to move the moon from place to place. Scientists are always suspicious of explanations that require a chain of unlikely coincidences. Also, on encountering Earth, the moon would have been moving so rapidly that Earth’s gravity would have unable to capture it without ripping the moon to fragments through tidal forces.

　　Until recently, astronomers were lt with no acceptable theory to explain the origin of the moon, and they occasionally joked that the moon could not exist. But during the 1970s, planetary astronomers developed a new theory that combines the best aspect of the fission hypothesis and the capture hypothesis.

　　The large-impact theory supposes that the moon formed from debris ejected into a disk around Earth by the impact of a large body. The impacting body may have been twice as large as Mars. In fact, instead of saying that Earth was hit by a large body, it may be more nearly correct to say that Earth and the moon resulted from the collision and merger of two very large planetesimals. The resulting large body became Earth, and the ejected debris formed the moon. Such an impact would have melted the proto-Earth, and the material falling together to form the moon would have been heated hot enough to melt. This theory fits well with the evidence from moon rocks that show the moon formed as a sea of magma.

　　This theory would explain other things. The collision must have occurred at a steep angle to eject enough matter to make the moon. The objects could not have collided head-on. A glancing collision would have spun the material rapidly enough to explain the observed angular momentum in the Earth-moon system. And if the two colliding planetesimals had already differentiated, the ejected material would be mostly iron-poor mantles and crust. Calculations show that the iron core of the impacting body could have fallen into the larger body that became Earth. This would explain why the moon is so poor in iron and why the abundances of other elements are so similar to those in Earth’s mantle. Finally, the material that eventually became the moon would have remained in a disk long enough for volatile elements, which the moon lacks, to be lost to space.

　　The moon may be the result of a giant impact. Until recently, astronomers have been reluctant to consider such catastrophic events, but a number of lines of evidence suggest that some planes may have been affected by giant impacts.

　　Question: Where did the Moon come from?

　　The Fission Theory: This theory proposes that the Moon was once part of the Earth and somehow separated from the Earth early in the history of the solar system. The present Pacific Ocean basin is the most popular site for the part of the Earth from which the Moon came. This theory was thought possible since the Moon&aposs composition resembles that of the Earth&aposs mantle and a rapidly spinning Earth could have cast off the Moon from its outer layers. However, the present-day Earth-Moon system should contain "fossil evidence" of this rapid spin and it does not. Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.

　　The Capture Theory: This theory proposes that the Moon was formed somewhere else in the solar system, and was later captured by the gravitational field of the Earth. The Moon&aposs different chemical composition could be explained if it formed elsewhere in the solar system, however, capture into the Moon&aposs present orbit is very improbable. Something would have to slow it down by just the right amount at just the right time, and scientists are reluctant to believe in such "fine tuning". Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.

　　The Condensation Theory: This theory proposes that the Moon and the Earth condensed individually from the nebula that formed the solar system, with the Moon formed in orbit around the Earth. However, if the Moon formed in the vicinity of the Earth it should have nearly the same composition. Specifically, it should possess a significant iron core, and it does not. Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.

　　There is one theory which remains to be discussed, and it is widely accepted today.

　　The Giant Impactor Theory (sometimes called The Ejected Ring Theory): This theory proposes that a planetesimal (or small planet) the size of Mars struck the Earth just after the formation of the solar system, ejecting large volumes of heated material from the outer layers of both objects. A disk of orbiting material was formed, and this matter eventually stuck together to form the Moon in orbit around the Earth. This theory can explain why the Moon is made mostly of rock and how the rock was excessively heated. Furthermore, we see evidence in many places in the solar system that such collisions were common late in the formative stages of the solar system. This theory is discussed further below.

　　背景知識：

　　一.分裂說。這是最早解釋月球起源的一種假設(shè)。月球本來是地球的一部分，后來由于地球轉(zhuǎn)速太快，把地球上一部分物質(zhì)拋了出去，這些物質(zhì)脫離地球后形成了月球，而遺留在地球上的大坑，就是現(xiàn)在的太平洋。這一觀點很快就收到了一些人的反對。他們認(rèn)為，以地球的自轉(zhuǎn)速度是無法將那樣大的一塊東西拋出去的。再說，如果月球是地球拋出去的，那麼二者的物質(zhì)成分就應(yīng)該是一致的?？墒峭ㄟ^對“阿波羅12號”飛船從月球上帶回來的巖石樣本進(jìn)行化驗分析，發(fā)現(xiàn)二者相差非常遠(yuǎn)。

　　二.俘獲說。這種假設(shè)認(rèn)為，月球本來只是太陽系中的一顆小行星，有一次，因為運行到地球附近，被地球的引力所俘獲，從此再也沒有離開過地球。還有一種接近俘獲說的觀點認(rèn)為，地球不斷把進(jìn)入自己軌道的物質(zhì)吸積到一起，久而久之，吸積的東西越來越多，最終形成了月球。但也有人指出，向月球這樣大的星球，地球恐怕沒有那麼大的力量能將它俘獲。

　　三.同源說。這一假設(shè)認(rèn)為，地球和月球都是太陽系中浮動的星云nebula，經(jīng)過旋轉(zhuǎn)和吸積，同時形成星體 celestial body (e.g. planet, satellite, etc.)。在吸積過程中，地球比月球相應(yīng)要快一點，成為“哥哥”。這一假設(shè)也受到了客觀存在的挑戰(zhàn)。通過對“阿波羅12號”飛船從月球上帶回來的巖石樣本進(jìn)行化驗分析，人們發(fā)現(xiàn)月球要比地球古老得多。有人認(rèn)為，月球年齡至少應(yīng)在70億年左右。

　　四.大碰撞說。這是近年來關(guān)于月球成因的新假設(shè)。這一假設(shè)認(rèn)為，太陽系演化早期，在星際空間曾形成大量的“星子”planetesimal，星子通過互相碰撞、吸積而長大。星子合并形成一個原始地球，同時也形成了一個相當(dāng)于地球質(zhì)量0.14倍的天體。這兩個天體在各自演化過程中，分別形成了以鐵為主的金屬核和由硅酸鹽silicate構(gòu)成的幔和殼。由于這兩個天體相距不遠(yuǎn)，因此相遇的機(jī)會就很大。一次偶然的機(jī)會，那個小的天體以每秒5千米左右的速度撞向地球。劇烈的碰撞不僅改變了地球的運動狀態(tài)，使地軸傾斜，而且還使那個小的天體被撞擊破裂，硅酸鹽殼和幔受熱蒸發(fā)，膨脹的氣體以及大的速度攜帶大量粉碎了的塵埃飛離地球。這些飛離地球的物質(zhì)，主要有碰撞體的幔組成，也有少部分地球上的物質(zhì)，比例大致為0.85:0.15。在撞擊體破裂時與幔分離的金屬核，因受膨脹飛離的氣體所阻而減速，大約在4小時內(nèi)被吸積到地球上。飛離地球的氣體和塵埃，并沒有完全脫離地球的引力控制，他們通過相互吸積而結(jié)合起來，形成全部熔融的月球，或者是先形成幾個分離的小月球，在逐漸吸積形成一個部分熔融meltdown的大月球

　　以上就是關(guān)于月球形成的三種學(xué)說的GMAT閱讀機(jī)經(jīng)的全部內(nèi)容，考生朋友可以有選擇的看看，最后需要提醒各位的是，機(jī)經(jīng)雖然會對我們解題有所幫助，但是在考場中即使題目很像也要避免秒選，最后祝大家都能考出好成績。