资源描述：
《英语六级冲刺阅读训练及答案(20篇)资料》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、一TheEarthcomprisesthreeprincipallayers:thedense,iron-richcore,themantlemadeofsilicate(硅酸盐)thataresemi-moltenatdepth,andthethin,solid-surfacecrustTherearetwokindsofcrust,aloweranddenseroceaniccrustandanupper，lightercontinentalcrustfoundoveronlyabout40pe
2、rcentoftheEarth'ssurface.Therocksofthecrustareofverydifferentages.Somecontinentalrocksareover3,000millionyearsold,whilethoseoftheoceanfloorarelessthan200millionyearsold.Thecrustsandthetop,solidpartofthemantle,totalingabout70to100kilometersinthickness,a
3、tpresentappeartoconsistofabout15rigidplates,7ofwhichareverylarge.Theseplatesmoveoverthesemi-moltenlowermantletoproduceallofthemajortopographical(地形学的)featuresoftheEarth.Activezoneswhereintensedeformationoccurareconfinedtothenarrow,interconnectingbounda
4、riesofcontactoftheplates. Therearethreemaintypesofzonesofcontact:spreadingcontactswhereplatesmoveapart,convergingcontactswhereplatesmovetowardseachother,andtransformcontactswhereplatesslidepasteachother.Newoceaniccrustisformedalongoneormoremarginsofea
5、chplatebymaterialissuingfromdeeperlayersoftheEarth'scrust,forexample,byvolcaniceruptions(爆发)oflava(火山熔岩)atmid-oceanridges.Ifatsuchaspreadingcontactthetwoplatessupportcontinents，arift(裂缝)isformedthatwillgraduallywidenandbecomefloodedbythetea.TheAtlantic
6、OceanformedlikethisastheAmericanandAfro-Europeanplatesmovedinoppositedirections.Whentwoplatescarryingcontinentscollide,thecontinentalblocks,toolighttobedrawndown,continuetofloatandthereforebuckle(起褶皱)toformamountainchainalongthelengthofthemarginofthepl
7、ates. 练习题： Choosecorrectanswerstothequestion: 1.TheEarth’scrust______. A.canbeclassifiedintotwotypes B.isformedalongthemarginsoftheplates C.consistsofsemi-moltenrocks D.isabout70to100kilometersthick 2.The15platesoftheEarthareformedfrom___. A.t
8、heoceaniccrustsandcontinentalcrusts B.thecrustsandthemantle C.thecrustsandthetopandsolidpartofthemantle D.thecontinentalcrustsandthesolidpartofthemantle 3.Seriously-deformedzonesappear_______ A.wheneverthecrustsmoveovermantle B.wh
