资源描述：
《英语六级冲刺阅读训练及问题详解(20篇)》由会员上传分享，免费在线阅读，更多相关内容在工程资料-天天文库。
1、实用标准文档一TheEarthcomprisesthreeprincipallayers:thedense,iron-richcore,themantlemadeofsilicate(硅酸盐)thataresemi-moltenatdepth,andthethin,solid-surfacecrustTherearetwokindsofcrust,aloweranddenseroceaniccrustandanupper，lightercontinentalcrustfoundoveronlyabout40perc
2、entoftheEarth'ssurface.Therocksofthecrustareofverydifferentages.Somecontinentalrocksareover3,000millionyearsold,whilethoseoftheoceanfloorarelessthan200millionyearsold.Thecrustsandthetop,solidpartofthemantle,totalingabout70to100kilometersinthickness,atpresentap
3、peartoconsistofabout15rigidplates,7ofwhichareverylarge.Theseplatesmoveoverthesemi-moltenlowermantletoproduceallofthemajortopographical(地形学的)featuresoftheEarth.Activezoneswhereintensedeformationoccurareconfinedtothenarrow,interconnectingboundariesofcontactofthe
4、plates. Therearethreemaintypesofzonesofcontact:spreadingcontactswhereplatesmoveapart,convergingcontactswhereplatesmovetowardseachother,andtransformcontactswhereplatesslidepasteachother.Newoceaniccrustisformedalongoneormoremarginsofeachplatebymaterialissuingfr
5、omdeeperlayersoftheEarth'scrust,forexample,byvolcaniceruptions(爆发)oflava(火山熔岩)atmid-oceanridges.Ifatsuchaspreadingcontactthetwoplatessupportcontinents，arift(裂缝)isformedthatwillgraduallywidenandbecomefloodedbythetea.TheAtlanticOceanformedlikethisastheAmericanan
6、dAfro-Europeanplatesmovedinoppositedirections.Whentwoplatescarryingcontinentscollide,thecontinentalblocks,toolighttobedrawndown,continuetofloatandthereforebuckle(起褶皱)toformamountainchainalongthelengthofthemarginoftheplates. 练习题： Choosecorrectanswerstotheques
7、tion: 1.TheEarth’scrust______. A.canbeclassifiedintotwotypes B.isformedalongthemarginsoftheplates C.consistsofsemi-moltenrocks文案大全实用标准文档 D.isabout70to100kilometersthick 2.The15platesoftheEarthareformedfrom___. A.theoceaniccrustsandcontinentalcrusts B.t
8、hecrustsandthemantle C.thecrustsandthetopandsolidpartofthemantle D.thecontinentalcrustsandthesolidpartofthemantle 3.Seriously-deformedzonesappear_______ A.wheneverthecrustsmove
