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Unit3-1Listening自然灾害和环境保护
Therearemanyformsoflivesonearth,includinghumanbeings.Lifeexistsinavarietyof
conditions.Someformsoflivesliveinthewateryenvironment,liketheoceans.Other
formsoflivescanbefoundinverydryareaslikedesserts.However,foranyformofliveto
exist,conditionsmustberight.Whentheconditionsaren’tright,thatformoflivescan
extinct.Tobecomeextinctmeanstodieoutcompletely.
Conditionsmustberightforlifetoexist.Millionsofyearsago,therewereformsoflives
thatnolongerexist.Whenconditionchanged,thisformoflifediedout.Oneextinction
eventhappenedabout250millionyearsago.Thisisthelargestextinctioneventofalltime.
Manyformsoflivesbecomeextinct.96%ofalllivesintheoceansdiedout.Mostinsects
alsobecameextinct.Thiseventhappenedoveraperiodofseveralmillionyears.The
causesofthisextinctioneventarestillunknown.Possiblecausesincludelargestvolcanic
eruptionsandglobalwarming.Somescientistsbelievethattherewereseveralcauses.
Theybelievethataseriesofeventscausedtheextinctions.Scientistsareworkingfor
betterunderstandwhatreallyhappened.
Inmoderntimes,wehumanbeingsfacechangingconditions.Forhumanstolive,we
needcleanairandcleanwater.Pollutionisnowagrowingproblemaroundtheworld.
Pollutionpoisonstheairandwaterthatwedependon.Pollutedairmakespeoplesickand
afraidtogetoutside.Pollutedwaterpoisonsourfoodsupply.Asaresult,weneverknow
whichfoodsaresafetoeat.Humanbeingscanbenotliveinapoisonedenvironment.
Therefore,pollutionisa
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