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
考研
There are some earth phenomena you can count on, but the magnetic field, some say, is not one of them. It fluctuates in strength
There are some earth phenomena you can count on, but the magnetic field, some say, is not one of them. It fluctuates in strength
admin
2015-01-15
78
问题
There are some earth phenomena you can count on, but the magnetic field, some say, is not one of them. It fluctuates in strength, drifts from its axis, and every few 100,000 years undergoes 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 metres of deep sea sediment(沉淀物)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 short terra, there seems to be an inevitable long-term decline preceding each polarity reversal. When the poles flip—a process that takes several hundred of 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 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 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, geo-physicists 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
根据文章第三段第四句话及第五、第六句话可知C项正确。
转载请注明原文地址:https://kaotiyun.com/show/Gqhi777K
0
在职申硕(同等学力)英语
相关试题推荐
Allexpertsagreethatthemostimportantconsiderationwithdietdrugsiscarefully______therisksandbenefits.
Computerswillflourishbecausetheyenableustoaccomplishtasksthatcouldneverbeforehavebeenundertaken.
Somepeoplefeelsadaboutglobalizationbecausetheybelieveitwill______Internetwasoriginallydesigned______
Intheend,bothattacksanddefensesofthefreemarketandconventionaleconomicshaveimmensephilosophicalimplications.
Whywasthehydraulicfuelpumpsealimportantforthespaceshuttle?WhichofthefollowingisNOTTRUEaccordingtowhatVoss
Woman:Youwerelateagainthismorning.Man:Sowhat?Question:Howdoesthemanreacttothewoman’sblame?
Man:IamsupposedtomeetJennythismorning.Ididwritedownheraddressonasheetofpaper,butnowithascompletelyslipp
Thetunnelsshouldbestrengthenedbecauseoftheir______toanattackthatcouldresultinmasscasualties.
ThecollapseoftheEarth’smagneticfield—whichguardstheplanetandguidesmanyofitscreatures—appearstohavestartedseri
随机试题
二氧化碳在血液中运输的主要形式是
西方列强对中国的侵略,首先和主要的是
简述情绪、情感与认识过程之间的区别与联系
背景资料:A公司承建一高层建筑建设工程,土建工程自行完成,机电工程分包给B公司施工,内容含有给水排水、通风与空调、建筑电气、建筑智能化工程、电梯和消防工程等多个专业分部工程;由于建筑物体量较大,需要跨3个年度才能完成约定的合同工期,因此虽然是一个单位工程
乙公司2007年3月发生如下业务:(1)3月3日,向B公司购买一批货物,向银行申请“现金银行汇票”用于结算货款。(2)3月7日,与C公司签订一份彩电购销合同。该合同规定:由C公司在10日内向乙公司提供彩电100台,货款共计25万元。
在市场上,()品牌主要占据了零售市场。
政治教育、思想教育与道德教育三者的关系中,表述正确的是()。
义和团运动爆发于山东的最直接的原因是()。
Ararepieceofgoodnewsfromtheworldofconservation:theglobalextinctioncrisismayhavebeenoverstated.Theworldisun
以下属于Python机器学习领域的第三方库的是()。
最新回复
(
0
)