2014高考英语 阅读理解精英训练题(5)

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1、2014高考英语阅读理解精英训练题（5）及答案阅读理解Thereisincreasingevidencethattheimpactsofmeteorites(陨星)havehadimportanteffectsonEarth,particularlyinthefieldofbiologicalevolution.SuchimpactscontinuetoposeanaturalhazardtolifeonEarth.Ifanimpactislargeenough,itcandisturbtheenvironmentoftheentireEarthandcauseanecologic

2、alcatastrophe.Thebest-documentedsuchimpacttookplace65millionyearsagoattheendoftheCretaceousperiod(白垩纪期)ofgeologicalhistory.ThisbreakinEarth'shistoryismarkedbyamassextinction,whenasmanyashalfthespeciesontheplanetbecameextinct.Whilethereareadozenormoremassextinctionsinthegeologicalrecord,theCret

3、aceousmassextinctionhasalwaysintriguedpaleontologists(古生物学者)becauseitmarkstheendoftheageofthedinosaurs.Fortensofmillionsofyears,thosegreatcreatureshadflourished.Then,suddenly,theydisappeared.ThebodythatimpactedEarthattheendoftheCretaceousperiodwasameteoritewithamassofmorethanatrilliontonsandad

4、iameterofatleast10kilometers.Scientistsfirstidentifiedthisimpactin1980fromtheworldwidelayerofsediment(沉积物)depositedfromthedustcloudthatenvelopedtheplanetaftertheimpact.Thissedimentlayerisenrichedintheraremetaliridium(铱)andotherelementsthatarerelativelyabundantinameteoritebutveryrareinthecrust(

5、地壳)ofEarth.Evendiluted(稀释)bytheterrestrial(地球的)materialexcavated(挖掘)fromthecrater,thiscomponentofmeteoritesiseasilyidentified.By1990geologistshadlocatedtheimpactsiteitselfintheYucatregionofMexico.Thecrater,nowdeeplyburiedinsediment,wasoriginallyabout200kilometersindiameter.Thisimpactreleasedan

6、enormousamountofenergy,excavatingacraterabouttwiceaslargeasthelunarcraterTycho.Theexplosionliftedabout100trilliontonsofdustintotheatmosphere.Suchaquantityofmaterialwouldhaveblockedthesunlightcompletelyfromreachingthesurface,plungingEarthintoaperiodofcoldanddarknessthatlastedatleastseveralmonth

7、s.Theexplosionisalsocalculatedtohaveproducedvastquantitiesofnitricacid(硝酸)andmeltedrockthatsprayedoutovermuchof-12-Earth,startingwidespreadfiresthatmusthaveconsumedmostterrestrialforestsandgrassland.Presumably,thoseenvironmentaldisaster