一、本月原始【by wllcynthia1986 】 第四个阅读是关于iced age的理论，第一段说某个astronoumer一个俄罗斯的名字提出了iced age是由于地球和太阳的什么flucuate造成的，这个理论在另一个人在shell 里面找到了什么deposit后得到证实。第二段是说某个人提出了一个新的证据，说是两个ice age之间的时间比原来认为地要长，第三段忘了... 二、考古 (!!!狗主认为最像的一个版本~如果有回来的同学反映这篇考古有问题，麻烦您联系一下我，我会后续跟进考古的) 【版本一】 同位素鉴定冰川和地球绕太阳轨道的关系OG上有相关的(就是用同位素鉴定冰川和地球绕太阳轨道的关系)，但是内容有所不同，这次是说(新狗，一屏不到，三段，熟读机经的人基本不用看都知道在讲什么) P1.介绍Milankovitch的理论，一句话带过，补充一点就是他的理论是1980s后由XXX发现ice sediment里的同位素之后才被科学家广为接受的(这里有题，说Milankovitch的理论是在XXX以后被科学家接受的，我选A sediment同位素研究出来之后) P2.介绍一个新的研究说是和这个理论有点不一致，说是ice的周期忽长忽短，还有其他比如火山因素会影响 P3.介绍Milankovitch本人对于这种不一直情况的说法，好像是承认有这种现象，(这里有题，主要是一个主旨题目说的是有两个选项比较纠结一个是A a new study about ice cycle 还有一个是evidence to chanllege an theory,楼主选了后者，这里话了不少时间考虑) 三、参考文章 (!!!狗主确定不是原文，虽然里面人的名字啊，理论啊是差不多的，但是考试时在第一段里一笔带过了) 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. P2.一个新发现可弥补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. P3.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. P4.其他的理论也不容忽视 四、参考资料 地球轨道根数变化与第四纪冰期 Changes of the Earth's 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。他认为，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
考生可收藏®无忧考网gmat频道，查看更多关于gmat考试相关的信息！！
