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 phenomena you can count on, but the magnetic field, someday, is not of them. It fluctuates in strength, drifts fr
There are some phenomena you can count on, but the magnetic field, someday, is not of them. It fluctuates in strength, drifts fr
admin
2010-12-25
92
问题
There are some 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 100000 years undergo, 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(沉淀物)core, they have obtained measurements lots 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 short 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 (熔化的)iron in the outer cote, 3000 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 ago. How and why they occur, however, has been widely debated. Several theories link polarity flips to external disasters such as meteor(陨星) 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、its identification of the origin of the earth’s magnetic field
B、the way the earth’s magnetic intensity is measured
C、its explanation of the shift in the earth’s polarity
D、the way the earth’s fluctuation rhythm is defined
答案
C
解析
文章表明,物理学家用不同的方法解释地球极性的转变。这两位物理学家用80米以下的深海沉积物做标本,而其他物理学家研究岩石里的矿物颗粒,以及有人认为是外部力量诸如陨星侵害来解释。第二段Using 80 meters of deep sea sediment(沉淀物)core,第三段By studying miner-al grains found in material ranging from rocks to clay articles.Several theories link polarity flips toexternal disasters such as meteor(陨星)impacts.
转载请注明原文地址:https://kaotiyun.com/show/N7IO777K
0
考博英语
相关试题推荐
Youwillhearadialogueonconferencearrangements.Foreachquestion(23-30),markoneletter(A,BorC)forthecorrectanswer.
Thenewoffice?Wherewouldyouratherdoyourwork:anicecoffeehouseorabusyoffice?Moreandmore,peopleareableto
•Readtheapplicationletterbelow.•Aresentences16-22ontheoppositepage’Right’or’Wrong’?Ifthereisnotenoughinform
•Readtheapplicationletterbelow.•Aresentences16-22ontheoppositepage’Right’or’Wrong’?Ifthereisnotenoughinform
MotivatingYourRetailSalesStaffinSlowTimesAlwaysgetinputfromyourstaffatthesemeetingsandhavesomefunwitha
LeadingtheStrategicChangesTheleaderisthechangestrategist,whoseroleistolead,tochampionthechanges,topromot
Theyachievedmorethantheyhadeverdreamed,lendingamagictotheirfamilystorythatnotaleorordinarylifecouldpossibl
TheEnglishvocabularyisknownfora(an)______ofwordswhicharecomparativelyseldomusedinordinaryconversations.
ProfessorJeffrey’slectureontherecyclingofwastepaperandothergarbagewillshowcanstillbeimproved.
TheballadandthefolksonghavelongbeenrecognizedasimportantKeystothethoughtsandfeelingsofapeople,butthedime
随机试题
制冷剂饱和温度与过热蒸气温度之差称为()。
A、慢性规律性的上腹痛B、无规律性的上腹痛C、右上腹绞痛D、左上腹剧痛E、全腹剧痛胆道结石,常表现
已知水柜无水时该水塔的基本自振周期为1.0,按《高耸结构设计规范》(GBJl35—90)计算该水塔在水柜重心高度处的风振系数βz,其值最接近于______项数值。若水柜重心高度处的风振系数βz=2.50,按《高耸结构设计规范》(GBJl35—90)计
根据存货经济订货模型,经济订货批量是能使订货成本与储存总成本相等的订货批量。()
物理学概念通常都很规范和严谨,物理学名词所表示的物理量都有明确的定义、计量方法和换算关系。对于暗能量,目前物理学家和宇宙学家对其仍一无所知。“暗能量”指的不过是当前宇宙学中最为深刻的一个难题。以下哪项陈述最适合接续上文作为它的结论?
简述正剧的由来及特点。
Therewasaperiodof______priortotheirdivorce,duringwhichshewentforatriparoundtheworldandhestayedathome.
Youngpeoplealwayssufferinrecessions.Employersstop【C1】______thembecausetheyareeasiertosack.Butin【C2】______episodes
CommercialVicesThecommercialvicesaregambling,prostitution,anddrugs.Theappealsofthecommercialvicesaresostron
PassageFourWhichwordisusedmetaphoricallyinParagraphSix?
最新回复
(
0
)