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, 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
2012-02-02
77
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, 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 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 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. (333 words)
The word "flip" (Line 7, Para. 2) most probably means "______".
选项
A、decline
B、intensify
C、fluctuate
D、reverse
答案
D
解析
转载请注明原文地址:https://kaotiyun.com/show/0Cna777K
本试题收录于:
艺术硕士(艺术基础)题库专业硕士分类
0
艺术硕士(艺术基础)
专业硕士
相关试题推荐
阅读案例:“芬兰诺基亚的崛起”,并回答问题。案例:芬兰诺基亚的崛起移动电话(手机)设备产业是20世纪90年代成长最快的产业之一。诺基亚在手机销售市场中占支配地位。诺基亚的根基在芬兰,一个人们在谈论尖端技术公司时通常想不到的国家
阅读案例:“芬兰诺基亚的崛起”,并回答问题。案例:芬兰诺基亚的崛起移动电话(手机)设备产业是20世纪90年代成长最快的产业之一。诺基亚在手机销售市场中占支配地位。诺基亚的根基在芬兰,一个人们在谈论尖端技术公司时通常想不到的国家
ItcameassomethingofasurprisewhenDiana,PrincessofWales,madeatriptoAngolain1997,tosupporttheRedCross’scamp
Thedeclineinmoralstandards—whichhaslongconcernedsocialanalysts—hasatlastcapturedtheattentionofaverageAmericans.
Thedeclineinmoralstandards—whichhaslongconcernedsocialanalysts—hasatlastcapturedtheattentionofaverageAmericans.
Somepessimisticexpertsfeelthattheautomobileisboundtofallintodisuse.Theyseeadayinthenot-too-distantfuturewhe
Inrecentyears,Israeliconsumershavegrownmoredemandingasthey’vebecomewealthierandmoreworldly-wise.Foreigntraveli
Accordingtotheairlineindustrystatistics,almost90%ofairlineaccidentsaresurvivableorpartiallysurvivable.Butpassen
Inthe1920sdemandforAmericanfarmproductsfell,asEuropeancountriesbegantorecoverfromWorldWarIandinstitutedaust
随机试题
许可证贸易
A.肾结核的血尿特点B.肾肿瘤的血尿特点C.肾结石的血尿特点D.肾盂肾炎的血尿特点E.膀胱炎的血尿特点终末血尿伴尿频、尿急、尿痛
属于无分流的先天性心脏病的是
机械通气进行雾化吸收时,其每次注入液体量不超过
女性,20岁,发热1周伴食欲减退、软弱。查体:体温39.6℃,脉搏74次/分,肝肋下2.0cm,脾肋下1.0cm,WBC2.6×109/L;N0.85,L0.14,嗜酸性粒细胞0.01,临床上拟诊为伤寒。为确定诊断对该患者应首选
土地的承包经营期限为()。
进行城市道路设计时,当建筑沿街部分长度超过150m或总长度超过()m时,应设穿过建筑的消防车道
属于进度纠偏的技术措施的是()。
心理学家安德森提出认知结构迁移理论,认为任何有意义的学习都是在原有学习的基础之上进行的,有意义的学习中一定有迁移。()
从A、B、C、D四个图形中选出最合适的一个,使得它保持左边四个图形所呈现的规律性:
最新回复
(
0
)