首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Milankovitch proposed in the early twentieth century that the ice ages were caused by variations in the Earth’s orbit around the
Milankovitch proposed in the early twentieth century that the ice ages were caused by variations in the Earth’s orbit around the
admin
2014-09-18
62
问题
Milankovitch proposed in the early twentieth century that the ice ages were caused by variations in the Earth’s orbit around the Sun. Eor sometime this the- ory was considered untestable, largely because there was no sufficiently precise chronology of the ice ages with which the orbital variations could be matched.
To establish such a chronology it is necessary to determine the relative amounts of land ice that 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 all the oxygen in water is oxygen 16, but a few molecules out of every thou- sand 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 will eventually return to it. Because heavier isotopes tend to be left-behind when water evaporates from the ocean surfaces, the remaining ocean wator becomes progressively enriched in oxygen 18. The degree of enrichment can be determined by analyzing ocean sediments of the period, because these sediments are composed of calcium carbonate shells of marine organisms, shells that were constructed with oxy- gen atoms drawn from the surrounding ocean. The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down.
As an indicator of shifts in the Earth’s climate, the isotope record has two advantages. First, it is 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, sedimentary evidence can be dat- ed 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 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.
However, it is important to note that other 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 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.
In the passage, the author is primarily interested in
选项
A、suggesting an alternative to an outdated research method.
B、introducing a new research method that calls an accepted theory into question.
C、emphasizing the instability of data gathered from the application of a new scientific method.
D、presenting a theory and describing a new method to test that theory.
E、initiating a debate about a widely accepted theory.
答案
D
解析
主题题型:A.对一过时方法给出替代法。显无。B.介绍一种否定了已被接受理论的新方法。无。C.强调数据的不稳定性。无。D.正确。给出一个新理论并且描述一个新方法验证这个理论。新理论即M的理论,新方法即文章的中心内容:同位素检测法。E.进行一个关于普遍接受的理论的争论。无。
转载请注明原文地址:https://kaotiyun.com/show/QctO777K
本试题收录于:
GMAT VERBAL题库GMAT分类
0
GMAT VERBAL
GMAT
相关试题推荐
In1947agroupoffamouspeoplefromtheartworldheadedbyanAustrianconductordecidedtoholdaninternationalfestivalof
Musiccomesinmanyforms:mostcountrieshaveastyleoftheirown.【C1】______theturnofthecenturywhenjazzwasborn,Ameri
Youshouldnot______goingtothedoctorbecauseyourillnessmightbeserious.
Itseemslikeeverydaythere’ssomenewresearchaboutwhetherourfavoritedrinksaregoodforus.Oneday,sciencesaysagla
Concerningmoneyoranythingelse,conflictsbetweenhusbandandwifeusuallyreflectapowerstruggle.Conflictsbetweenparent
Withthepossibleexceptionofequalrights,perhapsthemostcontroversialissueacrosstheUnitedStatestodayisthedeathpe
Atthebeginningoflastcentury,medicalscientistsmadeaninterestingdiscovery:wearebuiltnotjustoffleshandbloodbut
Theyneedtwentymoreworkers______theirgrouptodothejob.
Ithasbeenlaiddownthateachstudentmust______acompositiontotheteacheronceaweek.
Themoretimescientistsspenddesigningcomputers,themoretheywonderathumanbrain.Tasksthatpuzzlethemostadvancedsup
随机试题
《饮马长城窟行.青青河畔草》:远道不可思,_______。
A.头痛、呕吐,颈抵抗,克氏征阳性,布氏征阳性B.偏瘫,失语,多动,精神障碍C.截瘫,尿潴留,神经根痛D.头痛、呕吐,嗜睡,四肢肌张力增高E.前囟饱满,眼球不能外展,瞳孔不等大脑膜刺激症状是
老年糖尿病患者不建议使用()。
关于喷锚暗挖法隧道初期支护安全控制的说法,正确的有()。
某建设单位(甲方)拟开发居民小区。该小区位于市区,施工条件便利,相关手续已办理,勘察、设计工作已由受委托的勘察、设计单位完成。甲方进行公开招标,某施工单位(乙方)通过对招标文件的详细分析,认为居民楼设计采用框架-剪力墙结构过分保守。乙方在进行技术经济分析和
某企业进口一批材料,材料价款95万元,支付运抵我国口岸起卸前运费和保险费5万元,报关进口后发现其中的10%有严重的质量问题并将其退货,出口方为补偿该企业,发送价值10万元(含支付运抵我国口岸起卸前运费和保险费0.5万元)的无代价抵偿物,已知进口环节关税税率
红的、黄的、粉的,各色玫瑰,相继绽放,惹得人眼前一亮一亮,美丽的花朵________________了生活,普通的日子________________了些色彩、滋味和乐趣。填在横线上的词语最恰当的一项是()。
协调性精神运动性兴奋的表现包括()。(2010年5月真题)
Sendouta______signal,theshipissinking.
天才就是天生之才。()
最新回复
(
0
)