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
54
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.
The author of the passage would be most likely to agree with which of the following statements about the Milankovitch theory?
选项
A、It is the only possible explanation for the ice ages.
B、It is too limited to provide a plausible explanation for the ice ages, despite recent research findings.
C、It cannot be tested and confirmed until further research on volcanic activity is done.
D、It is one plausible explanation, though not the only one, for the ice ages.
答案
D
解析
态度题。根据题干关键词Milankovitch theory对原文定位。原文第二段第二句中的possible以及尾段第二句中的advantage,testable说明正评价,原文尾段尾句中的Yet(转折)和the lack ofinformation与选项D中的though not the only one对应。故答案为D(正评价,但不是唯一可行的理论)。
转载请注明原文地址:https://kaotiyun.com/show/JfLO777K
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
Americanwomenexperienceagreat【1】oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedormarried
Bythefirstdecadeofthe21stcentury,internationalcommercialairtrafficisexpected______vastlybeyondtoday’slevels.
Medicineachieveditssplendideminencebyapplyingtheprincipleoffragmentationtothehumancondition.Ourbodilyillshave
ThearomaofchocolateperfumestheairoftheRued’AssasinParis.EnteringChristianConstant’sstate-of-the-artboutique,yo
ThearomaofchocolateperfumestheairoftheRued’AssasinParis.EnteringChristianConstant’sstate-of-the-artboutique,yo
一位负责扶贫工作的官员说,到2004年底,尽管大多数贫困人口将解决温饱问题,还将有一些生活极端贫困的人们,他们还需要政府资助。此外,对于那些刚刚脱贫的人们,他们目前的生活状况必须改善,因为他们的生产和生活状况没有从根本上被改变。如果遭受自然灾害的袭击,就可
随机试题
TCP/IP协议具有什么特点?
小便涩痛可出现于下列哪些证候
为保证样本分布的()以及便于分配工作量和不同调查人员之间的工作衔接,在资料收集前必须划分调查区。
下列各项工作所需费用包含在设计合同价格中的有()。
在讲授七年级上册《秋天的怀念》之前,某教师为导入新课,向学生介绍本文作者史铁生的其他作品及作品集,以下介绍不正确的一项是()。
请认真阅读下列材料,并按要求作答。这些折痕相交于圆中心的一点,这一点叫作圆心,一般用字母O表示。连接圆心和圆上任意一点的线段叫作半径,一般用字母r表示。通过圆心并且两端都在圆上的线段叫作直径,一般用字母d表示。在同一个圆内,有多少条半径、多少条直径
2012年1—11月份,全国房地产开发投资64772亿元,同比名义增长16.7%,增速比1—10月份提高1.3个百分点。其中,东部地区房地产开发投资36719亿元,同比增长14.8%,增速比1—10月份提高0.5个百分点;中部地区房地产开发投资14035亿
地球以外的生命最大可能是存在于太阳系以外的某个行星。银河系本身包括1000亿个其他类似太阳的恒星,其中很多都可能有行星相随,这些行星与地球的相似程度足以使其成为生命的所在地。上面的陈述是以下面哪句为假设的?
Whichofthefollowingisthecorrectwaytotranscribeaphrasestructurerule?
A、He’stooexhaustedtocompete.B、He’sexcitedtheyareonthetop.C、He’safraidhewilllosetherace.D、Heprefersdoingexe
最新回复
(
0
)