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
21
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 precipitation formed from evaporated ocean water has______.
选项
A、the same isotopic ratio as ocean water
B、less oxygen 18 than does ocean water
C、less oxygen 18 than has the ice contained in continental ice sheets
D、a different isotopic composition than has precipitation formed from water on land
答案
B
解析
细节推理题。根据原文第二段第三句可知因为the heavier isotope 18(O18比较重),不太能蒸发出来;原文第二段第五句中的the remaining ocean water与选项B中的does ocean water对应;enriched in oxygen 18的是the remaining部分,与选项B中的比较级对应。故答案为B。
转载请注明原文地址:https://kaotiyun.com/show/XfLO777K
0
考博英语
相关试题推荐
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
WhileApplewascomingunderincreasingpressurefromlowercostPCclones,thecompany’sinitialresponsewastodevelopevenm
IhaveneverseenMrs.Clarkbefore,butIknowfromhermedicalchartandthereportIreceivedfromtheprecedingshiftthatt
Medicineachieveditssplendideminencebyapplyingtheprincipleoffragmentationtothehumancondition.Ourbodilyillshave
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcenturyandthediffusionofprintinginthe15thand1
【31】,opticalillusioncancuthighwaycrashes.Japanisacase【32】.Ithasreducedautomobilecrashesonsomeroads【33】nearly
随机试题
A.控制的标准必须是统一的、合理的B.有效控制系统应是合理、适用的C.控制手段应顾及例外情况的发生D.控制系统应能及时发现偏差信息E.有效控制系统依赖于准确的数据有效控制的特征中,“强调例外”指的是
下列具有燥湿与利尿功效的补气药是
下列哪项不属于报关员办理的业务?()
由凯米斯倡导的教育行动研究类型是
生态文明建设,是指人类在利用和改造自然的过程中,主动保护自然,积极改善和优化人与自然的关系,建设健康有序的生态运行机制和良好的生态环境。生态文明的核心是()
Thepoormanhadanappletree.TheKinggavethepoormanalotofmoney.
Whichofthefollowingistrue?
BreastfeedingChoosingwhethertobreastfeedorformulafeedyourbabyisoneofthefirstdecisionsexpectantparentswill
Ifpowerfulmeasures_______,thisareawouldhavebeenbadlypolluted.
A、Thedialogue.B、Themusic.C、Thestory.D、Theactors.A男士问女士对电影的看法,女士说她认为电影故事情节不怎么好,配乐一般,但台词挺幽默.由此可见,女士喜欢电影的台词。
最新回复
(
0
)