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
2015-04-24
22
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. For some time this theory 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 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 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 by analyzing ocean sediments of the period, because these sediments are composed of calcium carbonate shells of marine organisms, shells that were constructed with oxygen 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.
chronology <——land ice <——ration018/016
land ice <——sediments <------CaCO
3
(CC)<——ocean: O18/O16
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 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 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.
It can be inferred from the passage that the isotope record taken from ocean sediments would be less useful to researchers if which of the following was true?
选项
A、It indicated that lighter isotopes of oxygen predominated at certain times.
B、It had far more gaps in its sequence than the record taken from rocks on land.
C、It indicated that climate shifts did not occur every 100, 000 years.
D、It indicated that the ratios of oxygen 16 and oxygen 18 in ocean water were not consistent with those found in fresh water.
答案
B
解析
细节推断题。根据题干关键词the isotope record定位到原文第三段首句。下面两句中的continuous record(时间连续性)和little variation(地理连续性)与选项B对应,原句中的than…taken from rocks on land与选项B重现,原句中的that指的是the record。故答案为B。
转载请注明原文地址:https://kaotiyun.com/show/PfLO777K
0
考博英语
相关试题推荐
Inspiteofthe______economicforecast,manufacturingoutputhasrisenslightly.
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
Cultureshockmightbecalledan【1】diseaseofpeoplewhohavebeensuddenly【2】abroad.Likemostailments,ithasitsown【3】andc
Thereisanewtypeofsmalladvertisementbecomingincreasinglycommoninnewspaperclassifiedcolumns.Itissometimesplaced
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcenturyandthediffusionofprintinginthe15thand1
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcenturyandthediffusionofprintinginthe15thand1
TheeventsofSept.11haveratchetedupsecurityatAmericanairportstothehighestlevelever,accordingtoaspokesmanforT
各国文明的多样性,是人类社会的基本特征,也是推动世界文明进步的重要动力。当今世界拥有60亿人口,200多个国家和地区,2500多个民族,5000多种语言。由于历史传统、宗教信仰、文化背景、社会制度、价值观念和发展程度的不同,各国国家和地区才具有了各自鲜明的
随机试题
A.各类药品中的果味制剂、口服泡腾剂B.中药饮片C.中成药D.血液制品特殊适应证与急救、抢救需要时,才可以纳入基本医疗保险用药的药品是()。
下列关于向全国人大提出议案的表述中,正确的是哪一个?()
下列关于资产组的说法中正确的是()。
一般资料:韩某,女,18岁,汉族,高二年级学生求助者主诉:两个多月来求助者心情差,有时感到很绝望、郁闷,害怕考试,厌恶学习,不想见到老师同学,不想说话。求助者自述:从小就没有人真正关心我,爸爸只关心他的生意,而我妈对什么都漠不关心,对我也好
在一定时间内能把注意指向到几种不同的活动上,或在同时进行两种或几种活动的时候,把注意指向不同的对象,都属于注意的()。
在2002年中,新宾斯平销售量最大的月份是( )从表中可以看出,新宾斯平中,______规格的销售量最小。
下列各项哪些是法的基本特征()
深化文化体制改革要坚持()
WoodrowWilsonwasreferringtotheliberalideaoftheeconomicmarketwhenhesaidthatthefreeenterprisesystemisthemost
Language-basedlearningdisabilitiesareproblemswithage-appropriatereading,spelling,and/orwriting.Thisdisorderisnot
最新回复
(
0
)