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
72
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 calcium carbonate shells______.
选项
A、are not as susceptible to deterioration as rocks
B、are less common in sediments formed during an ice age
C、are found only in areas that were once covered by land ice
D、reflect the isotopic composition of the water at the time the shells were formed
答案
D
解析
细节推断题。根据题干关键词calcium carbonate shells定位到原文第二段第六句和尾句。原句中的The higher the ratio of oxygen 18 to oxygen 16与选项D中的the isotopic composition对应,原句中的the more land ice与选项D中的the shells对应,原句中的was laid down与选项D中的wereformed对应。故答案为D。
转载请注明原文地址:https://kaotiyun.com/show/TfLO777K
0
考博英语
相关试题推荐
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
Becausefuelsuppliesarefiniteandmanypeoplearewasteful,wewillhavetoinstall______solarheatingdeviceinourhome.
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcenturyandthediffusionofprintinginthe15thand1
TheeventsofSept.11haveratchetedupsecurityatAmericanairportstothehighestlevelever,accordingtoaspokesmanforT
【31】,opticalillusioncancuthighwaycrashes.Japanisacase【32】.Ithasreducedautomobilecrashesonsomeroads【33】nearly
中俄油气合作目前发展的势头很好,在未来合作的道路上,可能还会遇到各种各样的困难,有时甚至会出现挑战大于机遇的情况。中俄双方现在都已认识到,中俄油气合作是大势所趋,对双方谋划后金融危机时代本国经济的发展,都有着重大的战略意义。尤其是对中方而言,在经济全球化的
ThearomaofchocolateperfumestheairoftheRued’AssasinParis.EnteringChristianConstant’sstate-of-the-artboutique,yo
随机试题
一项经纪业务的最终完成,其作用的最终是()。
会计电算化的近期计划应与中长期计划相适应。 ( )
下列表述有误的是()。
普通附息债券的凸性()。
下列选项中属于我国证券登记结算机构业务范围和职能的有()。Ⅰ.接受上市申请,安排证券上市Ⅱ.证券的存管和过户Ⅲ.证券持有人名册登记Ⅳ.受发行人的委托派发证券权益
丁墨在他的小说《他来了,请闭眼》中,塑造了高智商、严谨和善于推理的犯罪心理学家薄靳言的形象,这属于()。
在我国远古社会的传说中,相传()品尝百草,救民疾苦,发明了原始医药;“耕而作陶”,发明了原始制陶业;教人耕种,出现了原始农业和原始文化
如果你是老师,该怎样激发学生的学习动机?
半殖民地半封建中国的资产阶级分为大资产阶级和小资产阶级两部分。
AHealthProfileAhealthprofileisaportraitofallofthefactorsthatinfluenceyourhealth.Todrawyourhealthprofil
最新回复
(
0
)