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
44
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
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
Thereisanewtypeofsmalladvertisementbecomingincreasinglycommoninnewspaperclassifiedcolumns.Itissometimesplaced
Somepoliticiansarescurryingaboutwithmuchzestandanticipation.It’stime,theirpollsinformthem,tofindthequickfix
Medicineachieveditssplendideminencebyapplyingtheprincipleoffragmentationtothehumancondition.Ourbodilyillshave
Japaneseworkersstillputinanimpressive42hourseachweekbuttheyare______bytheSouthKoreansandSingaporeanswhospen
Comparisonsweredrawnbetweenthedevelopmentoftelevisioninthe20thcenturyandthediffusionofprintinginthe15thand1
随机试题
网络营销
险库是指尾矿库安全设施存在严重隐患,若不及时处理将会导致垮坝事故的尾矿库。对险库必须()。
建设项目管理“三项制度”中不包括()。
某公司6月期初存货500件,单价25元,(存货按照实际成本法核算)当月原材料收发情况如下:(1)5日,购入200件材料,增值税专用发票上注明价款5600元,增值税税率17%,材料尚未到达,签发商业承兑汇票支付货款。(2)7日,购入200件材料运抵企业验
不属于培训需求分析的方法是()。
以下外币交易日会计处理中,不正确的是()。
请阅读下面录像题的情景叙述,找出情景叙述中秘书行为及工作环境中正确或错误的地方(应至少找出15处正误点)。宏远公司总经理助理高叶办公室,办公室内没有绿色植物(特写),窗帘已拉上,遮住了外面的强光。电脑和打印机摆放有序。高叶着便装坐在办公桌前办公。
公文的主体部分包括()。
一个由于没有获得打印机而不能运行的进程处于
TheEnglishLanguageEnglishisthemost【T1】______languageintheworldandismorewidelyspokenandwrittenthan【T2】______
最新回复
(
0
)