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
The Theory of Continental Drift has had a long and turbulent history since it was first proposed by Alfred Wegener in 1910. (46)
The Theory of Continental Drift has had a long and turbulent history since it was first proposed by Alfred Wegener in 1910. (46)
admin
2010-09-06
48
问题
The Theory of Continental Drift has had a long and turbulent history since it was first proposed by Alfred Wegener in 1910. (46)
Vigorously challenged yet widely ignored, the theory had languished for half a century, primarily due to its lack of a plausible mechanism to support the proposed drift.
With the discovery of sea-floor spreading in the late 1950’s and early 60’s, the idea was reinvigorated. Plate tectonics is now almost universally accepted. Many details of the mechanism are to be worked out.
The surface of the Earth is divided into approximately six large plates, plus a number of smaller ones. The plates are bounded by an interconnected network of ridges, transform faults, and trenches. Ridges, also called spreading centers, occur where two plates are moving away from each other. As the plates separate, hot molten mantle material flows up to fill the void. (47)
The increased heat resulting from this flow reduces the density of the plates, causing them to float higher, thus elevating the boundaries by many thousands of feet above the colder surrounding sea floor.
(48)
Ridges on the ocean floor form the longest continuous ranges of mountains on the planet, but only in a very few places on the Earth do these mountains rise above the ocean surface.
New sea floor is constantly being created along spreading centers. Obviously somewhere else old sea floor must be going away. This occurs in trenches, also called subduction zones. Trenches occur along the boundary between two plates that are moving towards each other. (49)
Where this occurs, one plate is bent downwards at about a 40°angle and plunges under the other plate’s leading edge, eventually to melt back into the liquid mantle below.
As the subducting plate is heated back up to mantle temperatures, certain minerals in the plate melt sooner than others. (50)
Minerals that melt at lower temperatures and are lighter than the surrounding material tend to rise, melting their way up through the overriding plate to erupt as volcanoes on the ocean floor.
As these volcanoes grow, they rise above the ocean surface to form lines of islands along the leading edge of the overriding plate. Numerous islands of Micronesia and Melanesia in the western Pacific were created in this way.
选项
答案
这种流动所产生的不断增加的热量降低了板块的密度,使板块再向上漂移,将边界提升,从而使其超出周围较冷海底数千英尺的高度。
解析
转载请注明原文地址:https://jikaoti.com/ti/IH7RFFFM
0
考研英语一
相关试题推荐
Anewstudyfoundthatinner-citykidslivinginneighborhoodswithmoregreenspacegainedabout13%lessweightoveratwo-yea
TransatlanticfrictionbetweencompaniesandregulatorshasgrownasEurope’sdataguardianshavebecomemoreassertive.Frances
Theauthorthinksthepresentrushtoputcomputersintheclassroomis______.Accordingtotheauthor,basiccomputerskills
Theauthorthinksthepresentrushtoputcomputersintheclassroomis______.Thebeliefthateducationisindispensabletoa
Forhim(tobere-elected),whatisessentialisnotthathispolicy(works),(butthat)thepublicbelievethatit(is).
Thecapitalintendedtobroadentheexportbaseand______efficiencygainsfrominternationaltradewaschanneledinsteadofu
Theauthorisprimarilyconcernedwith_____.ItcanbeinferredfromthetextthatAmericanhistorytextbooksusedtoassertt
Asoneworkswithcolorinapractical,orexperimentalway,oneisimpressedbytwoapparentlyunrelatedfacts.Colorasseeni
Foodisdifferentfromareatoarea.TheFrencharefamousfortheirsauces,theItalianspraised【C1】______theirpasta-foodfrom
In1879,RichardHenryPrattfoundedtheCarlisleIndianSchool,aremarkable40-yearchapterinthiscountry’sfailedsocialpo
随机试题
关于产褥期保健,说法错误的是
诸病有声,鼓之如鼓,皆属于
患者,女,40岁,心悸,PDE检查示左心房黏液瘤,该患者心脏听诊可闻及
根据《建设工程安全生产管理条例》的规定,施工单位实施爆破、起重吊装等工程时,应当安排现场的监督人员是()。
【2013专业知识真题上午卷】在变电所设计和运行中应考虑直接雷击、雷电反击和感应雷电过电压对电气装置的危害,其直击雷过电压保护可采用避雷针或避雷线,下列设施应装设直击雷保护装置的有哪些?()
()又称优惠利率贷款,是由亚行开发基金提供的贷款,贷款的期限为40年,含10年的宽限期,不收利息,仅收1%的手续费,此种贷款只提供给还款能力有限的发展中国家。
毛泽东诗词“一桥飞架南北,天堑变通途”中的“一桥”是指()。
组建计算机网络的目的是为了实现资源共享,这里的计算机资源主要是指硬件、软件和()。
有如下程序#include<stdio.h>main(){inti;for(i=0;i<5;i++)putchar(’9’-i);printf("\n");}程序运行后的输出结果是
TheTribalLawandOrderActisto
最新回复
(
0
)