首页
登录
职称英语
Milankovitch proposed in the early twentieth century that the ice ages were
Milankovitch proposed in the early twentieth century that the ice ages were
游客
2025-02-26
10
管理
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. Eor sometime this the- ory 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 thou- sand 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 wator 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 oxy- gen 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.
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 dat- ed 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. [br] According to the passage, which of the following is(are)true of the ice ages? I . The last ice age occurred about 25,000 years ago. II. Ice ages have lasted about 10, 000 years for at least the last several hundred thousand years. III. Ice ages have occurred about every 100,000 years for at least the last several hundred thousand years.
选项
A、I only
B、II only
C、III only
D、I and II only
E、I , II and III
答案
C
解析
哪一个关于冰期的说法是正确的?I.最近一次出现在两万五千年前。文中未提。Ⅱ.至少最近几十万年,冰期延续了一万年。文中无。Ⅲ.至少最近几十万年,每十万年出现一次。这是文中L52—55的明确说法。∴C.Ⅲonly
转载请注明原文地址:https://tihaiku.com/zcyy/3973729.html
相关试题推荐
Milankovitchproposedintheearlytwentiethcenturythattheiceageswere
Milankovitchproposedintheearlytwentiethcenturythattheiceageswere
Milankovitchproposedintheearlytwentiethcenturythattheiceageswere
Milankovitchproposedintheearlytwentiethcenturythattheiceageswere
Milankovitchproposedintheearlytwentiethcenturythattheiceageswere
So-calledenvironmentalistshavearguedthattheproposedGoldenLakeDevelopmen
Overthelastcentury,paleontologistshaveusedsmalldifferencesbetweenfossi
Tocqueville,anineteenth-centurywriterknownforhisstudyofdemocracyinthe
Theseventeenth-centuryphysicistSirIsaacNewtonisrememberedchieflyforhis
Riothamus,afifth-centurykingoftheBritons,wasbetrayedbyanassociate,fo
随机试题
[audioFiles]2016m12s/audio_ezfj_201610_018[/audioFiles]Children’sHealth
Directions:Forthispart,youareallowed30minutestowriteashortessayent
企业是安全生产的责任主体,也是安全生产标准化建设的主体。()
落锤式弯沉仪组成不包括()A.荷载发生装置 B.弯沉检测装置 C.载重汽车
什么是幼儿园一日生活常规(2分)试述培养幼儿一日生活常规意义和方法。(18分)
资本一帝国主义列强对中国不但进行军事侵略、政治控制,还对中国进行经济掠夺。其对中
下列哪项不是MDS的特点?( )A.老年多见 B.血细胞病态造血 C.易转
《孔乙己》中下列行为及说法符合现代法律规定的是()A.丁举人打折孔乙己的腿
物流成本管理的主要方法有( )。A.比较分析法 B.定量分析法 C.综合评价
关于多品种小批量型生产物流特征的说法,错误的是()。A.物料被加工的重复程度介于
最新回复
(
0
)