2021_2022学年新教材高中英语Unit3ConservationSectionⅠTopicTalk&Lesson1TheSixthExtinction课件北师大版选择性必修第一册.ppt

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1、Unit3ConservationSectionⅠTopicTalk&Lesson1TheSixthExtinction晨读晚诵导语:人类不能是这个孤独星球上的唯一幸存者。Theremightbeasmanyas10millionspeciesofcomplex1lifeonthisplanettoday—ahugenumber.Butaddupallofthecomplexspeciesthateverlivedandsomebiologiststhinkthegrandtotalwouldbeaboutfive

2、billion.Theestimate2leadstoanastonishingconclusion:astaggering99%ofspeciesarenotaroundanymore.Theyhavebeendriventoextinction.Theremightbeasmanyas10millionspeciesofcomplex1lifeonthisplanettoday—ahugenumber.Butaddupallofthecomplexspeciesthateverlivedandsomebiolo

3、giststhinkthegrandtotalwouldbeaboutfivebillion.Theestimate2leadstoanastonishingconclusion:astaggering99%ofspeciesarenotaroundanymore.Theyhavebeendriventoextinction.Morespeciesarejoiningtheranksoftheextincteveryyear.Manyscientistsbelievewearelivingthroughanepis

4、ode(一段经历)ofremarkablyrapidextinction,onascalethathasbeenseenonlyfivetimesinthelasthalfabillionyears.Theycallthiscurrentepisodethesixthmassextinction—alarge,globaldeclineinawidevarietyofspeciesoverarelativelyshortperiodoftime.Andtheytendtoagreethathumansarethem

5、aincause.Over-hunting,overfishing,andhuman-drivenhabitatlossarepushingmanyspeciestothebrink.Infact,wehavechangedtheplanetsomuchthatsomegeologistsarenowsuggestingthatwehaveenteredanewphase3inEarth’shistory;anepochtheycallthe“Anthropocene”.By2100,itisexpectedtha

6、thumanswillhavecausedtheextinctionofuptohalfoftheworld’scurrentspecies.Becausewearelivingthroughthisextinction,itisrelativelyeasyforustostudythedrivingforcesbehindit.Buthowdowedeterminewhatcausedothermassdie-offsthathappenedlongago?Todosowehavetolookatwhatarch

7、aeologists,paleontologists,geologistsandotherscientistshaveconcludedfromtheevidencetheyhavegathered.Thetroubleis,thosescientistsdonotalwaysagreewithoneanother—evenaboutthemostrecentextinctionevent.Aswellasthefive-orsix-massextinctions,therehavealsobeenmanysmal

8、lerextinctions.OneoftheseminiextinctioneventshappenedtowardstheendofthePleistocene,afewtensofthousandsofyearsago.Itissometimescalledthe“megafaunaextinction”becausemanyofthespeciesi