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
There are some earth phenomena you can count on, but the magnetic field, someday is not of them. It fluctuates in strength, drif
There are some earth phenomena you can count on, but the magnetic field, someday is not of them. It fluctuates in strength, drif
admin
2013-11-29
45
问题
There are some earth phenomena you can count on, but the magnetic field, someday is not of them. It fluctuates in strength, drifts from its axis, and every few 100, 000 years undergo a dramatic polarity reversal -a period when north pole becomes south pole and south pole becomes north pole. But how is the field generated, and why is it so unstable?
Groundbreaking research by two French geophysicists promises to shed some light on the mystery. Using 80 meters of deep sea sediment core, they have obtained measurements of magnetic-field intensity that span 11 polarity reversals and four million years. The analysis reveals that intensity appears to fluctuate with a clear, well-defined rhythm. Although the strength of the magnetic field varies irregularly during the shout term, there seems to be an inevitable long term decline preceding each polarity reversal. When the poles flip-a process that takes several hundred thousand years — the magnetic field rapidly regains its strength and the cycle is repeated.
The results have caused a stir among geophysicists. The magnetic field is thought to originate from molten iron in the outer core, 3, 000 kilometers beneath the earth’s surface. By studying mineral grains found in material ranging from rocks to clay articles, previous researchers have already been able to identify reversals dating back 170 million years, including the most recent switch 730, 000 years age. How and why they occur, however, has been widely debated. Several theories link polarity flips to external disasters such as meteor impacts. But Peter Olson, a geophysicist at the Johns Hopkins University in Baltimore, says this is unlikely if the French researchers are right In fact, Olson says intensity that predictably declines from one reversal to the next contradicts 90 percent of the models currently under study. If the results prove to be valid, geophysicists will have a new theory to guide them in their quest to understand the earth’s inner physics. It certainly points the direction for future research.
The French geophysicists’ study is different from currently prevailing theories in _____.
选项
A、ist identification of the origin of the earth’s magnetic field
B、the way the earth’s magnetic intensity is measured
C、ist explanation of the shift in the earth’s polarity
D、the way the earth’s fluctuation rhythm is defined
答案
A
解析
可从文中第三段的内容推知,即这些结果引起了地球物理学家们的震惊,人们认为磁场源于地表下3000公里处地核外层熔化的铁。后面又说,在巴尔的摩的约翰斯一霍布金斯大学的地球物理学家彼得·奥尔森说,如果法国研究者正确的话,这几种理论就不可能成立了。奥尔森说,实际上两次转换间预计的衰落强度同90%的现行研究模式相矛盾。如果这些结果证明正确,地球物理学家将会有一种新理论来指导他们探索地球内部物理学。它的确为将来的研究指出了方向。
转载请注明原文地址:https://kaotiyun.com/show/DUhO777K
0
考博英语
相关试题推荐
Largecompaniesneedawaytoreachthesavingsofthepublicatlarge.Thesameproblem,onasmallerscale,facespracticallyev
Oflate,therehavebeenseveralpostssuggestingthatAmericahasnocultureorthatwhatcultureithasissomehowinferiorto
Theyearsbetween1870and1895broughtenormouschangestothetheaterintheUnitedStatesastheresidentcompanywasundermi
InJuly,almostunnoticedbythenationalpress,adeadlybirdvirusarrivedonapheasantfarminSurrey.ExpertsfromtheDepa
Theinfluenceofthemoralstandardsofthehomeisevident.Ifthereisnorecognitionofthedifference【B1】______rightand
Everysecond,【56】hectareoftheworld’srainforestisdestroyed.That’sonetotwofootballfields.This【57】rateofdestruct
Mailservicewillbetemporarily______becauseofthestrikeofthepostalworkers.
Thefridgeisconsideredanecessity.Ithasbeensosincethe1960swhenpackagedfoodfirstappearedwiththelabel:"storein
Intheprecedingchapter,economicwelfarewastakenbroadlytoconsistofthatgroupofsatisfactionsanddissatisfactionswhic
Whilehiseffortsweretremendoustheresultsappearedtobevery______.
随机试题
甲因怀孕被取保候审期间,干扰证人作证。其保证人乙明知但没有阻止,也没有报告公安机关。公安机关可对乙罚款,数额为500元以上1万元以下。
经济法律关系的构成要素中不包括()。
盛唐边塞诗派的代表诗人是()
依据《工贸企业有限空间作业安全管理与监督暂行规定》的规定,有限空间作业应当严格遵守()的原则。
在中国境内投资的德国企业,会计记录()。
在保险业务相关要素中,()只能由单位担任,不能是个人。
—Whatwereyoudoingthistimeyesterday?—Iwasteaching______English______theinternet.
某班为了准备茶话会,分别派了甲乙丙丁四个同学去采买糖果点心和小纪念品等。甲买回来的东西,乙全都买了,丙买回的东西包括了乙买的全部,丁买回的东西里也有丙买的东西。由此可以推断:
WhatdidtheprofessorwanttotalktoAnnabout?
Agoodtranslatorisbydefinitionbilingual.Theoppositeisnot【C1】______true,however.Abornandbredbilingualwillstill
最新回复
(
0
)