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Stephen1《新世纪研究生公共英语教材阅读A》课文Unit3OceanofSandFromTheGuardian1.Thereismoredesertsthansunandsand.Onthesetwopagesyoucanfindouthowplants,animalsandpeoplemanagetosurviveintheseapparentlybarrenplaces.2.Alldesertsaredry.Thehot,sandyplaceswethinkofwhenwetalkaboutdesertsaresubtropicaldeserts.TheyarefoundneartheTropicsofCancerandCapricornwherethewarmairwhichrisesattheEquatorsinksdownagain,givingaclimateofclearskiesandverylowrainfall.TheSaharaisalmostone-thirdthesizeofAfrica,andisnearlyasbigastheU.S.A.,thefourthlargestcountry.Itwasnotalwaysadesert.Overmillionsofyearsithasbeenconveredinice,sea,forestsandgrasslands.3.Desertwindsareusuallydry.Somedesertsarein“rainshadow”areaswherethewindshavelostwhatmoisturetheyhadcrossinghighground.Othersareinthemiddleofcontinentswherethewindsblowingoverthemhavelostanymoisturegainedfromdistantoceans.TheGobidesertinMongoliainAsiaisanexampleofsuchaninlanddesert.TheAtacamainnorthernChileisthedriestdesertonEarth.Partsofthedeserthadnorainfor400years,from1570to1971,andinotherparts,rainshadneverbeenrecordedn.OneofthesandiestdesertsistheTaklaMakan.Sandstormscanwhipupthesandashighas3,048m(10.000ft).WindblownsandintheSaharacanbesofiercethatitwillsandblastthepointoffacaroraeroplane.Thetemperatureatnightinahotdesertcandropbelowfreezing,to-4℃(24℉).Duringtheday,thesandcanbeashotas79℃(175℉).Livinginadesertclimate4.Desertsaredifficultplacesinwhichtolive.Duringthedaytheyareveryhot.IntheLibyanDesertinNorthAfricathetemperatureon13September1922reached58Cintheshade!Butdesertnightsareoftencoldbecauseclearskiesallowheattoescapeintotheatmosphere.Thelackofwatercausedbylowrainfallisbadenough,butrainfallisalsohighlyunpredictable.Yearsofdroughtcanendintremendousrainstorms.Manydesertareasarebarerock,orarecoveredwithpebblesandgravel.Sandaccountsforonlyabout15percentoftheearth’sdesertregions.Insomedeserts,thetotalrainfortheyearmightfallinonlytwoorthreestorms.Butthatisenoughforplantseedstosproutandbloom,turningpartsofthedesertintocarpetsofflowersforafewdays.Howplantssurvive5.Withinafewhoursofrainfalling,thousandsoffloweringplantswillstarttoappear.Seedsofplantssuchasthedesertdandelionlieinthegroundforyearswaitingfortherain.6.Theseplantsdieasthedesertdriesoutagain,leavingtheirseedsforthenextrains.Otherplantshaveadaptedtotheharshenvironmentbystoringwaterintheirleaves,stemsorroots.TheAmericansaguarocactuscanhold6to8tonesofwater.Desertplantsoftenhavespreadingrootsystemswhichextracteverydropofmoisturefromtheground.Therootsofthemesquitebushcanbe20mdeep.7.Plantsgenerallylosewaterthroughporesintheirleaves.Topreventthis,desertplantshavesmallwaxyleavesandfewerpores.Manyclosetheirporesduringthedaysotheydonotlosemoisture.Toprotectthemselvesagainstgrazinganimals,someplantshavethornsoranunpleasantStephen2taste.Cactiareprotectedbytheirsharpspines.CactiarefoundonlyinAmericandeserts.Thetallestaresaguaroswhichcanreach15m(50ft)tall,weigh7tonsandlivefor200years.Waterisstoredinthestemandusedintimesofdrought.Animallife8.Althoughdesertsseemempty,fewarewithoutanimals.Mostanimalsshelterfromthedaytimeheatinholesorburrows.Theburrowstrapmoisturearestaycoolerthanthegroundabove.Inthecoolereveningoratdawn,theanimalsemerge.9.Smallermammalsoftenhavelargeears.Duringtheday,theanimallosesheatthroughitsears.Inthedark,largewarntheanimalofunseendangers.10.Reptilesventuringoutindaytimetrytoavoidtouchingthehotsand.TheAustralianbeardedlizardsometimesrunsonitshindlegsonly.Theaptlynamedsidewindersnakeonlytouchesthegroundintwoplaces.11.Alldesertanimalssurviveonlittlewater.Manysmallanimalsliveonthemoistureintheirfood.Largeranimalssuchasthecamelcangowithoutwaterfordays,butdrinkhugeamountswhentheygetthechance.Acamelcandrink10litresofwaterinaminute.Desertpeoples12.Overthoughtofyears,peoplehavelearnthowtosurviveinDeserts.TheSanpeopleoftheKalaharidesertinsouthernAfricaandtheAustralianAborigineshuntanimalsandgatherfoodplants.Theylearntraditionalskillsfromolderpeople.13.Ontheedgesofthedesert,nomadicpeoplesgrazeflocksofsheepandgoats.Theyareconstantlymovingtofresherpastures.NomadssuchastheTuaregoftheSaharainNorthAfricawearloosechothingtoprotectthemsandandheat.Tuaregmenprotecttheirfaceswithaveil.14.Insomedeserts,oases(fertileareas)formaroundwellsorsprings.Aroundoasestherearesettlementsandsomethingfarms.Themud-brickhousesarekeptcoolbytheirthickwindowlesswalls.Onthemove15.Desertsarespreading.Already12percentoftheworld‘slandisdesert,andeveryyearanother12millionhectaresbecomeuselessforfarming.Asthefollowingshows，desertificationhasmanycauses.Theendresultisthatthesoilbecomesexposedandiseasilyeroded.16.Throughouttheworld，governmentsandaidagenciestrytopreventdesertification.Therearenosimpleanswers,butsuccessfulprojectshavehelpedpeopleinpoorercountriestohelpthemselves.Theschemesuseknowledgeandresourcesthatarereadilyavailabletolocalcommunities.Theyinclude:plantingtreesandhedgestoprotectcropsfromgrazinganimalsandwinderosion.Insomeareas，peoplehavebuiltlinesofstonesacrossslopestopreventrainwaterrunningawayandtoallowittosoakintothesoil.Unit4ThreeKindsofFatigueFatigueisoneofthemostcommoncom