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1、懂你英语L4-Unit21ExtinctionEventsLevel4Unit21Listening?ExtinctionEventsTheEarthwasformedabout4.6billionyearsago.Thefirstlifeappearedaboutabillionyearslater.Thefirstplantsdidntappearuntilaround2billionyearsago.Untilabout580millionyearsago,lifeformsweresmallandmicroscopic.Sincethattime,lifehasevolvedintom
2、anydifferenttypes,orspecies.However,scientistsestimatethatmorethan99%ofthemarenowextinct.TherehavebeenseveralextinctioneventsinthehistoryoftheEarth.Inanextinctioneventmanylifeforms,orspeciesoflife,dieout.Thecausesofmassextinctioneventsareunsolvedmysteries.Theseeventsarenotpredictableandcanhappenatan
3、ytime.Scientiststhinkthatsomeofthemwerestartedbyasteroidimpactsorvolcaniceruptions.Eventslikethesecanchangetheglobalconditionsthatlifedependson.Onemajorextinctioneventhappenedabout66millionyearsago.ThateventmayhavebeenstartedbyalargeasteroidthathittheEarth.Asaresult,thedinosaursandabouthalfofallspec
4、iesontheplanetdiedout.Whentheasteroidhittheearth,itstartedachainofevents.Achainofeventsisaseriesofeventslinkedtogether,likeachain.Thisparticularchainofeventshappenedoveraperiodofmonthsandyears.WhentheasteroidhittheEarth,itcausedahugecloudofdusttoentertheatmosphere.Thiscloudofdustblockedthesunanddark
5、enedtheEarthformanymonths.Withoutenoughsunlight,plantsandplant-eatinganimalsquicklydied.Withthedeathsofsomanyplantsandanimals,thefoodchaincollapsed.Thisledtothedeathsofmanymorespecies.Massextinctioneventshaveplayedanimportantpartintheevolutionoflife.Infact,someextinctioneventshavehelpedtoacceleratee
6、volution.Forexample,somemammalslivedthroughtheageofthedinosaurs,buttheycouldntcompete.Whenthedinosaurswereremoved,themammalswereabletocompetemoresuccessfully.Oncetheycouldcompete,mammalsevolvedtoahigherstate.Withoutextinctionevents,perhapswewouldntbeheretoday.Scientistsestimatethattherehavebeenatlea
7、st5massextinctionsinthelast540millionyears.Theyalsobelievethatwehaveenteredanewextinctionevent.Speciesarebecomingextinctatamuchfasterratethanbefore.Insteadofasteroidsorvolcaniceruptions,thecurrenteventistheresultofhumanactivities.Humanactivities,forexample,haveledtoglobalwarming.Globalwarmingisthere
8、sultofanincreaseincarbongasesinouratmosphere.Thesegasestrapheatfromthesun,sotheEarthisgettingwarmer.Asaresult,sealevelsarerisingandweatherpatternsarechanging.Inaddition,wehumansaredestroyingthehabitatsofmanyplantsandanimals.Cuttingdownforestsandpollutingriversdestroysthehabitatsofmanyformsoflife.The
9、reisnolongeranydoubtthatthisishappening.Speciesoflifearedisappearingatanincreasingrate.Globaltemperaturesarerisingandweatherpatternsarechanging.Scientistsarewarningusthatfastactionisnecessarytosaveourfuture.Ifwedontact,wemaygothewayofthedinosaurs.(Thisnewextinctioneventiscausedbyhumans.)BodySystemsL
10、evel4 Unit2 1 VocabularyThebodyscirculatorysystemincludestheheartandbloodvessels.Theheartpumpsbloodtoallpartsofthebodythroughanetworkofarteriesandveins.(Thebloodvesselsthatcarryoxygen-richbloodfromtheheartarecalledarteries.)Thedigestivesystembreaksdownandabsorbsfoodintothebody.Itssuppliestheenergyth
11、atthebodyneedsforgrowthandrepair.Afterdigestion,excessfoodisturnedintowasteandeliminatedfromthebody.(Thedigestivesystemiswherefoodisbrokendownandabsorbedintothebody.)Thenervoussystemincludesthebrain,spinalcordandnerves.Thisisyourbodyscontrolsystem.Itcontrolsyourmusclesandorgans,includingyourcirculat
12、oryanddigestivesystem.(Thenervoussystemregulatesyourheartbeatanddigestion.)Therespiratorysystemincludesthenoseandlungs.Itbringsairandoxygenintothebodyandremovescarbondioxide.Thelungsarewhereoxygenentersthebloodstream,andcarbondioxideisremoved.Theimmunesystemprotectsthebodyagainstinfectionsanddisease
13、s.Sneezingandfeverareexamplesofhowtheimmunesystemworks.Ifaninfectioninvadesthebody,theimmunesystemattacksit.GreatDiscoveriesThecontrolleduseoffireallowedpeopletocookfoodandsurviveinthecolderclimates.Fireprovidedlightsothatpeoplecouldworkandsocializeforlongerhours.Withtheinventionofagriculture,people
14、couldgrowfoodandsettleintocommunities.Bygrowingfood,peoplecouldspendlesstimehunting,andmoretimeforotherthingssuchasart.(Withthedevelopmentofagriculture,peoplehadmoretimeforotheractivities.)Thedomesticationofanimalsallowedpeopletoraiseanduseanimalsforfoodandwork.Byraisingherdsofanimalssuchassheep,hum
15、anshadaregularsupplyofmeatandclothing.Thestrengthofanimalssuchashorsesandoxenwasusedforworkandtransportation.Thedevelopmentoftoolsandmachineshasresultedinmoreefficient?manufacturingandconstruction.Withbettertoolsandmachines,workcanbedonewithfewerpeopleandatmuchlowercosts.(Theuseofmachineshasreducedt
16、henumberofpeopleneededtomakethings.)Thedevelopmentofscienceandengineeringhasimprovedmanythings,includingcommunications.Withanunderstandingofelectricity,telephonesandradiosallowpeopletocommunicateoverlongdistances.(Scienceandengineeringhavechangedthewaywecommunicatewitheachother.)Level4Unit2Part1DialogueSmartphoneAddictionItookavacationlastnight.Whatareyoutalkingabout?Wheredidyoutakeyourvacation?Ididntgoanywhere.Ijustspendane
