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
43
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
Insteadofansweringthequestion,themanager______hisshouldersasifitwerenotimportant.
Theunpopularmeasurefinally______thedownfallofthegovernment.
Wewantyoutodescribealltheeventsofthatmorninginsequencewithoutanydelay.
Daltonwonderedwhytheheavierandlightergasesintheatmospheredidnotseparateasoilandwaterdo.Hefinallyconcludedt
Daltonwonderedwhytheheavierandlightergasesintheatmospheredidnotseparateasoilandwaterdo.Hefinallyconcludedt
ThecollapseoftheEarth’smagneticfield—whichguardstheplanetandguidesmanyofitscreatures—appearstohavestartedseri
ThecollapseoftheEarth’smagneticfield—whichguardstheplanetandguidesmanyofitscreatures—appearstohavestartedseri
Althoughitseemedtotakeallherstrength,thepatient______upasmiletohermom.
Therearesomeearthphenomenayoucancounton,butthemagneticfield,somesay,isnotoneofthem.Itfluctuatesinstrength
随机试题
按《药品管理法》列入劣药的是哪个
男,45岁,下颌骨升支部区无痛性肿大。镜下可见肿瘤上皮增殖成网状联结,周边不是一层柱状细胞,中心部细胞类似于星网层细胞。上皮岛内呈现广泛的鳞状化生,可见角化珠的形成,病理诊断为
患者,男,48岁,临床诊断为骨关节炎,同时伴有胃溃疡,请药师确认应当禁用的药物是
采用市场比较法评估求得的土地价格,称为积算价格。()
合同分析的基本内容的包括()。
根据民法理论,( )。
根据许多学者的研究,个体归因时往往遵从()。
一、注意事项1.申论考试,与传统作文考试不同,是对分析驾驭材料的能力与对表达能力并重的考试。2.作答参考时限:阅读资料40分钟,作答110分钟。3.仔细阅读给定的资料,按照后面提出的“申论要求”依次作答。二、给定资料材料一
感知综合障碍是指病人在感知某一现实事物时,作为一个客观存在的整体来说是正确的,但对该事物的个别属性,如大小、形状、颜色、空间距离等产生与该事物不相符合的感知。根据上述定义,下列属于感知综合障碍的是()。
使用SQL语句将学生表S中年龄(AGE)大于30岁的记录删除,正确的命令是
最新回复
(
0
)