®無憂考網(wǎng)為大家整理了2013年7月GMAT閱讀機經(jīng)：Ice Age,僅供參考！！

　一、本月原始【by wllcynthia1986 】 　　第四個閱讀是關(guān)于iced age的理論，第一段說某個astronoumer一個俄羅斯的名字提出了iced age是由于地球和太陽的什么flucuate造成的，這個理論在另一個人在shell 里面找到了什么deposit后得到證實。第二段是說某個人提出了一個新的證據(jù)，說是兩個ice age之間的時間比原來認為地要長，第三段忘了... 　　二、考古 　　(!!!狗主認為最像的一個版本~如果有回來的同學(xué)反映這篇考古有問題，麻煩您聯(lián)系一下我，我會后續(xù)跟進考古的) 　　【版本一】 　　同位素鑒定冰川和地球繞太陽軌道的關(guān)系OG上有相關(guān)的(就是用同位素鑒定冰川和地球繞太陽軌道的關(guān)系)，但是內(nèi)容有所不同，這次是說(新狗，一屏不到，三段，熟讀機經(jīng)的人基本不用看都知道在講什么) 　　P1.介紹Milankovitch的理論，一句話帶過，補充一點就是他的理論是1980s后由XXX發(fā)現(xiàn)ice sediment里的同位素之后才被科學(xué)家廣為接受的(這里有題，說Milankovitch的理論是在XXX以后被科學(xué)家接受的，我選A sediment同位素研究出來之后) 　　P2.介紹一個新的研究說是和這個理論有點不一致，說是ice的周期忽長忽短，還有其他比如火山因素會影響 　　P3.介紹Milankovitch本人對于這種不一直情況的說法，好像是承認有這種現(xiàn)象，(這里有題，主要是一個主旨題目說的是有兩個選項比較糾結(jié)一個是A a new study about ice cycle 還有一個是evidence to chanllege an theory,樓主選了后者，這里話了不少時間考慮) 　　三、參考文章 　　(!!!狗主確定不是原文，雖然里面人的名字啊，理論啊是差不多的，但是考試時在第一段里一筆帶過了) 　　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.

　P1.M提出一個理論, 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]碳酸鈣) 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. 　P2.一個新發(fā)現(xiàn)可彌補M理論的缺陷 　　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. 　　P3.新發(fā)現(xiàn)的優(yōu)點 　　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. 　 　P4.其他的理論也不容忽視 　　四、參考資料 　　地球軌道根數(shù)變化與第四紀(jì)冰期 Changes of the Earth's Orbital Elements and the Quaternary Glacial Epoch 　　米蘭柯維奇(Milankovitch)天文氣候?qū)W理論和第四紀(jì)地質(zhì)時期以來冰期的研究進展.研究結(jié)果表明,地球上的冰體積具有近10萬yr的變化周期,并伴有近4萬yr和2萬yr的變化周期,它們是由于地球的軌道根數(shù)變化導(dǎo)致的氣候變遷所致;不同的地球物理資料中均存在上述類似的變化周期,表明氣候變遷所導(dǎo)致的變化是全球性效應(yīng),證實米蘭柯維奇天文理論是基本正確的。他認為，北半球高緯夏季太陽輻射變化是驅(qū)動第四紀(jì)冰期旋回的主因。這個理論的核心是單一敏感區(qū)的觸發(fā)驅(qū)動機制，即北半球高緯氣候變化信號被放大、傳輸進而影響全球。最近，由于大量高分辨率及精確定年的氣候變化記錄的獲得，從以下4個方面構(gòu)成了對米氏理論的挑戰(zhàn)：1)一些低緯地區(qū)并沒有明顯的10萬年冰量周期，而是以2萬年歲差周期為主，表明北半球冰蓋的擴張、收縮變化并沒有完全控制低緯區(qū)的氣候變化;2)在最近幾次冰消期時，南半球和低緯區(qū)的溫度增高，要 早于北半球冰蓋的融化，表明冰消期的觸發(fā)機制并非是北半球高緯夏季太陽輻射;3)大氣CO2濃度在第2冰消期的增加同南極升溫相一致，表明該時大氣CO2 濃度增加亦有可能早于北半球冰蓋消融;4)南半球的末次冰盛期有可能早于北半球。這就說明單一敏感區(qū)觸發(fā)驅(qū)動機制已難以圓滿解釋所有觀察事實，天文因素控制下軌道尺度氣候變化機制研究正面臨理論突破的新需求和新機遇

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