懂你英语Level 3 unit 3讲课讲稿.doc

《懂你英语Level 3 unit 3讲课讲稿.doc》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、精品好文档，推荐学习交流Level3unit3part1ListeningTherearemanyformsoflifeonEarth,includinghumanbeings.Lifeexistsinavarietyofconditions.Someformsoflifeliveinawateryenvironment,liketheoceans.Otherformsoflifecanbefoundinverydryareas,likedeserts.However,foranyformoflifetoexist,conditionsmustberight.Whenconditi

2、onsarenotright,thatformoflifewillbecomeextinct.Tobecomeextinctmeanstodieoutcompletely.-Whatmustberightforlifetoexist?-Conditions.-Whathappensifconditionsarenotright?–Lifecannotexist.Conditionsmustberightforlifetoexist.Millionsofyearsago,therewereformsoflifethatnolongerexist.Whenconditionschang

3、ed,theseformsoflifediedout.Oneextinctioneventhappenedabout250millionyearsago.Thiswasthelargestextinctioneventofalltime.Manyformsoflifebecameextinct.96%ofalllifeintheoceansdiedout.Mostinsectsalsobecameextinct.Thiseventhappenedoveraperiodofseveralmillionyears.-Whathappenedabout250millionyearsago

4、?–Manyformsoflifebecameextinct.-Whathappensinanextinctionevent?–Manyformsoflifebecameextinct.Thecausesofthisextinctioneventarestillunknown.Possiblecausesincludelargevolcaniceruptionsandglobalwarming.Somescientistsbelievethattherewereseveralcauses.仅供学习与交流，如有侵权请联系网站删除谢谢30精品好文档，推荐学习交流Theybelievet

5、hataseriesofeventscausedtheextinctions.Scientistsareworkingtobetterunderstandwhatreallyhappened.-Whatistheonepossiblecauseofthisevent?–Volcaniceruptions.Inmoderntimes,wehumansfacechangingconditions.Forhumanstolive,weneedcleanairandcleanwater.Pollutionisnowagrowingproblemaroundtheworld.Pollutio

6、npoisonstheairandwaterthatwedependon.Pollutedairmakespeoplesickandafraidtogooutside.Pollutedwaterpoisonsourfoodsupply.Asaresult,weneverknowwhichfoodsaresafetoeat.Humanbeingscannotliveinapoisonedenvironment.Therefore,pollutionisamajorthreattoourexistence.-Whatdohumansneedtolive?–Cleanairandclea

7、nwater.-Whatpoisonstheairandwater?–Pollution.Humansneedtemperaturestobeinacomfortablerange.Tobeinacomfortablerangemeanstobeneithertoohotnortoocold.Withglobalwarming,globaltemperaturesarerising.Astemperaturesrise,thepolaricecapswillmelt.