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, 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
2010-07-14
8
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 meters 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 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 un. likely 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
推理题。根据最后一段第五句,很多理论学家将磁极转换的原因归结为外部灾难,如陨星撞击,法国学者的结论与此明显不同。
转载请注明原文地址:https://kaotiyun.com/show/5b7K777K
0
大学英语六级
相关试题推荐
A、Hehashurthishand.B、Hecan’tfixit.C、Heisverybusyatthemoment.D、Hewantsthewomantogivehimahand.C本题的关键在于第二个
Nocountryshouldbeallowedto__________________(干涉其他国家的内部事务).
Recentlymoreandmoreattentionhasbeenfocusedtotheproblemofpreservingthe
A、Adelicateart.B、Areligion.C、Anexactscience.D、Awayoflife.B原文中说“Yogaisnotareligion”,所以瑜珈不能归为宗教。
Foraboutthreecenturieswehavebeendoingscience,tryingscienceout,usingsciencefortheconstructionofwhatwecallmod
Foraboutthreecenturieswehavebeendoingscience,tryingscienceout,usingsciencefortheconstructionofwhatwecallmod
A、Surfingtilenet.B、Watchingatalkshow.C、Packingabirthdaygift.D、Shoppingatajewelrystore.A根据对话中女性提到的youareonthe
MildweatherhasbroughtJapan’smuch-lovedcherrytreesinto【B1】______twoweeksearlythisyear,butnoteveryoneis【B2】__
A、Atadrugstore.B、Atahospital.C、Atadoctor’soffice.D、Atadentist’soffice.A男士说“我需要一些阿司匹林,并帮我把这个处方的药配一下。”女士说“好的。这是你要的阿司
A、Becauseshecannotfindahusbandforherself.B、Becausethefemalespiderislargerthanthemaleone.C、Becausethefemales
随机试题
患者,男,50岁,咽部异物感1个月,肝炎病史20年,进一步检查,首先应考虑
A.烦躁不安,高声尖叫B.口唇樱桃红色,前囟凹陷C.呼吸深而快D.口吐泡沫,唇周青紫E.肝脾肿大伴黄疸符合新生儿败血症的症状是
A总承包单位承接一综合楼工程,建筑面积163000m2,工期:500日历天,质量标准:合格,该工程实行工程监理。建筑层数:地上22层,地下2层,基础类型为桩基筏式承台板,结构为现浇剪力墙,混凝土采用预拌混凝土,屋面防水采用SBS改性沥青防水卷材,外立面为玻
古人把教师的职责归结为“传道”、“授业”、“解惑”,其实质是()。
“实干才能梦想成真。”以新思想引领新征程,坚忍不拔、锲而不舍,保持永不懈怠的精神状态和________的奋斗姿态,我们脚下的路必然将联通无尽的未来,在一代又一代人的接续奋斗中________更美好的明天。填入画横线部分最恰当的一项是:
对相对简单而本质上又连续的新行为进行连续接近的强化是
系统地提出动机的归因理论是哪位心理学家?()
在《集安高句丽壁画》一书中,作者称图一为“剁肉图”,把古人右手所持工具看作菜刀;后有研究者结合该书“烤肉串”和“厨师扇风”的图片,认为古人右手拿的是史称“便面"的中国古扇,因此应叫“烤肉图”。对文物图像命名中存在的不同见解,应坚持的正确观点是(
证明:D=
计算不定积分
最新回复
(
0
)