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
39
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
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
TestshaveconfirmedthatfourpeopleinWisconsincontractedthemonkeypoxvirusaftercomingintoclosecontactwithpetprair
Becausefuelsuppliesarefiniteandmanypeoplearewasteful,wewillhavetoinstall______solarheatingdeviceinourhome.
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
PresidentBushcametohisparent’scentury-oldsummerhomeontheMainecoastforalittlerelaxation,adistantcousin’sweddi
Britishcancerresearchershavefoundthatchildhoodleukaemiaiscausedbyaninfection,andclustersofcasesaroundindustria
Priortothe20thcentury,manylanguageswithsmallnumbersofspeakerssurvivedforcenturies.Theincreasinglyinterconnected
中国已经发展成为一个全球极富吸引力的、现实的大市场。世界各国和地区不少有远见卓识的企业家,都将目光投向了中国,并从投资活动中获得了丰厚的回报。我相信,中国加入世贸组织后,外商参与中国投资活动的机会将越来越多,自身发展的空间也越来越大。在中国的投资活动一定能
随机试题
某矿一平巷盲竖井的罐笼在提升矿石时发生卡罐故障,罐底被撞开,罐笼内约1t的矿石掉落井底,罐笼被卡在离井口2~3m的位置不能上下移动。当班的绞车工张某随即上井向值班矿长元某A和维修工陈某报告,陈某和元某A先后下井进行检查和修理工作。其间,陈某在没有采取任何防
患者女性24岁,因左上智齿颊向高位阻生,要求拔除在行左上颌结节麻醉时,出现左颊面部血肿,其原因是
A、茄科B、夹竹桃科C、萝蘼科D、蔷薇科E、唇形科紫苏叶来源于
患者,女性,34岁。G1P0,孕16周出现心慌、气短,经检查发现心功能Ⅱ级。经过增加产前检查次数,严密监测孕期经过等,目前孕37周,自然临产。该产妇在分娩期正确的护理措施是
根据《安全生产许可证条例》,下列选项中不属于企业取得安全生产许可证的条件的是()。
某中外合资经营企业的投资总额为410万美元,在其注册资本中,中方认缴的出资额为105万美元。根据外商投资企业法律制度的规定,外方认缴的出资额至少为()万美元。
2013年5月,为规范和加强国家级公益林保护、经营和管理,国家林业局会同财政部联合下发了《国家级公益林管理办法》。《办法》指出,国家级公益林管理遵循()的原则。
当事物处在量变状态时,()。
设y=f(x)有二阶连续导数,且满足xy“+3xy‘2=1-e-x.若f(x)在x=c(c≠0)处取得极值,证明f(c)是极小值.
Ourschoollibraryis______closedforrepairs.
最新回复
(
0
)