新东方背诵文选全集下.docx
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新东方背诵文选全集下
新东方背诵文选全集(下)
35OilRefining
Animportantnewindustry,oilrefining,grewaftertheCivilwar.Crudeoil,orpetroleum-adark,thickoozefromtheearth-hadbeenknownforhundredsofyears,butlittleusehadeverbeenmadeofit.Inthe1850’sSamuelM.Kier,amanufacturerinwesternPennsylvania,begancollectingtheoilfromlocalseepagesandrefiningitintokerosene.Refining,likesmelting,isaprocessofremovingimpuritiesfromarawmaterial.
Kerosenewasusedtolightlamps.Itwasacheapsubstituteforwhaleoil,whichwasbecominghardertoget.Soontherewasalargedemandforkerosene.Peoplebegantosearchfornewsuppliesofpetroleum.
ThefirstoilwellwasdrilledbyE.L.Drake,aretiredrailroadconductor.In1859hebegandrillinginTitusville,Pennsylvania.Thewholeventureseemedsoimpracticalandfoolishthatonlookerscalledit“Drake’sFolly”.Butwhenhehaddrilleddownabout70feet(21meters),Drakestruckoil.Hiswellbegantoyield20barrelsofcrudeoiladay.
NewsofDrake’ssuccessbroughtoilprospectorstothescene.Bytheearly1860’sthesewildcattersweredrillingfor“blackgold”alloverwesternPennsylvania.TheboomrivaledtheCaliforniagoldrushof1848initsexcitementandWildWestatmosphere.Anditbroughtfarmorewealthtotheprospectorsthananygoldrush.
Crudeoilcouldberefinedintomanyproducts.Forsomeyearskerosenecontinuedtobetheprincipalone.Itwassoldingrocerystoresanddoor-to-door.Inthe1880’srefinerslearnedhowtomakeotherpetroleumproductssuchaswaxesandlubricatingoils.Petroleumwasnotthenusedtomakegasolineorheatingoil.
36PlateTectonicsandSea-floorSpreading
Thetheoryofplatetectonicsdescribesthemotionsofthelithosphere,thecomparativelyrigidouterlayeroftheEarththatincludesallthecrustandpartoftheunderlyingmantle.Thelithosphereisdividedintoafewdozenplatesofvarioussizesandshapes,ingeneraltheplatesareinmotionwithrespecttooneanother.Amid-oceanridgeisaboundarybetweenplateswherenewlithosphericmaterialisinjectedfrombelow.Astheplatesdivergefromamid-oceanridgetheyslideonamoreyieldinglayeratthebaseofthelithosphere.
SincethesizeoftheEarthisessentiallyconstant,newlithospherecanbecreatedatthemid-oceanridgesonlyifanequalamountoflithosphericmaterialisconsumedelsewhere.Thesiteofthisdestructionisanotherkindofplateboundary:
aseductionzone.Thereoneplatedivesundertheedgeofanotherandisreincorporatedintothemantle.Bothkindsofplateboundaryareassociatedwithfaultsystems,earthquakesandvolcanism,butthekindsofgeologicactivityobservedatthetwoboundariesarequitedifferent.
Theideaofsea-floorspreadingactuallyprecededthetheoryofplatetectonics.Initsoriginalversion,intheearly1960’s,itdescribedthecreationanddestructionoftheoceanfloor,butitdidnotspecifyrigidlithosphericplates.ThehypothesiswassubstantiatedsoonafterwardbythediscoverythatperiodicreversalsoftheEarth’smagneticfieldarerecordedintheoceaniccrust.Asmagmarisesunderthemid-oceanridge,ferromagneticmineralsinthemagmabecomemagnetizedinthedirectionofthemagmabecomemagnetizedinthedirectionofthegeomagneticfield.Whenthemagmacoolsandsolidifies,thedirectionandthepolarityofthefieldarepreservedinthemagnetizedvolcanicrock.Reversalsofthefieldgiverisetoaseriesofmagneticstripesrunningparalleltotheaxisoftherift.Theoceaniccrustthusservesasamagnetictaperecordingofthehistoryofthegeomagneticfieldthatcanbedatedindependently;thewidthofthestripesindicatestherateofthesea-floorspreading.
37Icebergs
Icebergsareamongnature’smostspectacularcreations,andyetmostpeoplehaveneverseenone.Avagueairofmysteryenvelopsthem.Theycomeintobeing-----somewhere------infaraway,frigidwaters,amidthunderousnoiseandsplashingturbulence,whichinmostcasesnoonehearsorsees.Theyexistonlyashorttimeandthenslowlywasteawayjustasunnoticed.
Objectsofsheerestbeautytheyhavebeencalled.Appearinginanendlessvarietyofshapes,theymaybedazzlinglywhite,ortheymaybeglassyblue,greenorpurple,tintedfaintlyofindarkerhues.Theyaregraceful,stately,inspiring-----incalm,sunlightseas.
Buttheyarealsocalledfrighteninganddangerous,andthattheyare----inthenight,inthefog,andinstorms.Eveninclearweatheroneiswisetostayasafedistanceawayfromthem.Mostoftheirbulkishiddenbelowthewater,sotheirunderwaterpartsmayextendoutfarbeyondthevisibletop.Also,theymayrolloverunexpectedly,churningthewatersaroundthem.
Icebergsarepartsofglaciersthatbreakoff,driftintothewater,floataboutawhile,andfinallymelt.Icebergsafloattodayaremadeofsnowflakesthathavefallenoverlongagesoftime.Theyembodysnowsthatdrifteddownhundreds,ormanythousands,orinsomecasesmaybeamillionyearsago.Thesnowsfellinpolarregionsandoncoldmountains,wheretheymeltedonlyalittleornotatall,andsocollectedtogreatdepthsovertheyearsandcenturies.
Aseachyear’ssnowaccumulationlayonthesurface,evaporationandmeltingcausedthesnowflakesslowlytolosetheirfeatherypointsandbecometinygrainsofice.Whennewsnowfellontopoftheold,ittooturnedtoicygrains.Soblanketsofsnowandicegrainsmountedlayeruponlayerandwereofsuchgreatthicknessthattheweightoftheupperlayerscompressedthelowerones.Withtimeandpressurefromabove,themanysmallicegrainsjoinedandchangedtolargercrystals,andeventuallythedeepercrystalsmergedintoasolidmassofice.
38Topaz
Topazisahard,transparentmineral.Itisacompoundofaluminum,silica,andfluorine.Gemtopazisvaluable.Jewelerscallthisvarietyofthestone“precioustopaz”.Thebest-knownprecioustopazgemsrangeincolorfromrichyellowtolightbrownorpinkishred.Topazisoneofthehardestgemminerals.Inthemineraltableofhardness,ithasaratingof8,whichmeansthataknifecannotcutit,andthattopazwillscratchquartz.
Thegoldenvarietyofprecioustopazisquiteuncommon.Mostoftheworld’stopaziswhiteorblue.Thewhiteandbluecrystalsoftopazarelarge,oftenweighingthousandsofcarats.Forthisreason,thevalueoftopazdoesnotdependsomuchonitssizeasitdoeswithdiamondsandmanyotherpreciousstones,wherethevalueincreasesaboutfourtimeswitheachdoublingofweight.Thevalueofatopazislargelydeterminedbyitsquality.Butcolorisalsoimportant:
bluetopaz,forinstance,isoftenirradiatedtodeepenandimproveitscolor.
Bluetopazisoftensoldasaquamarineandavarietyofbrownquartziswidelysoldastopaz.Thequartzismuchlessbrilliantandmoreplentifulthantruetopaz.Mostofitisvarietyofamethyst:
thatheathasturnedbrown.
39TheSalinityofOceanWaters
Ifthesalinityofoceanwatersisanalyzed,itisfoundtovaryonlyslightlyfromplacetoplace.Nevertheless,someofthesesmallchangesareimportant.Therearethreebasicprocessesthatcauseachangeinoceanicsalinity.Oneoftheseisthesubtractionofwaterfromtheoceanbymeansofevaporation---conversionofliquidwatertowatervapor.Inthismannerthesalinityisincreased,sincethesaltsstaybehind.Ifthisiscarriedtotheextreme,ofcourse,whitecrystalsofsaltwouldbeleftbehind.
Theoppositeofevaporationisprecipitation,suchasrain,bywhichwaterisaddedtotheocean.Heretheoceanisbeingdilutedsothatthesalinityisdecreased.Thismayoccurinareasofhighrainfallorincoastalregionswhereriversflowintotheocean.Thussalinitymaybeincreasedbythesubtractionofwaterbyevaporation,ordecreasedbytheadditionoffreshwaterbyprecipitationorrunoff.
Normally,intropicalregionswherethesunisverystrong,theoceansalinityissomewhathigherthanitisinotherpartsoftheworldwherethereisnotasmuchevaporation.Similarly,incoastalregionswhereriversdilutethesea,salinityissomewhatlowerthaninotheroceanicareas.
Athirdprocessbywhichsalinitymaybealteredisassociatedwiththeformationandmeltingofseaice.Whenseawaterisfrozen,thedissolvedmaterialsareleftbehind.Inthismanner,seawaterdirectlymaterialsareleftbehind.Inthismanner,seawaterdirectlybeneathfreshlyformedseaicehasahighersalinitythanitdidbeforetheiceappeared.Ofcourse,whenthisicemelts,itwilltendtodecreasethesalinityofthesurroundingwater.
IntheWeddellSeaAntarctica,thedensestwaterintheoceansisformedasaresultofthisfreezingprocess,whichincreasesthesalinityofcoldwater.Thisheavywatersinksandisfoundinthedeeperportionsoftheoceansoftheworld.
40Cohesion-tensionTheory
Atmosphericpressurecansupportacolumnofwaterupto10metershigh.Butplantscanmovewatermuchhigher;thesequoiatreecanpumpwatertoitsverytopmorethan100metersabovetheground.Untiltheendofthenineteenthcentury,themovementofwaterintreesandothertallplantswasamystery.Somebotanistshypothesizedthatthelivingcellsofplantsactedaspumps.Butmanyexperimentsdemonstratedthatthestemsofplantsinwhichallthecellsarekilledcanstillmovewatertoappreciableheights.Otherexplanationsforthemovementofwaterinplantshavebeenbasedonrootpressure,apushonthewaterfromtherootsatthebottomoftheplant.Butrootpressureisnotnearlygreatenoughtopushwatertothetopsoftalltrees.Furthermore,theconifers,whichareamongthetallesttrees,haveunusuallylowrootpressures.
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