案例教案成果tpo053the cambrian explosion

TheCambrianThegeologictimescaleismarkedbysignificantgeologicandbiologicalevents,includingtheoriginofEarthabout4.6billionyearsago,theoriginoflifeabout3.5billionyearsago,theoriginofeukaryoticlife-forms(livingthingsthathavecellswithtruenuclei)about1.5billionyearsago,andtheoriginofanimalsabout0.6billionyearsago.ThelasteventmarksthebeginningoftheCambrianperiod.AnimalsoriginatedrelativelylateinthehistoryofEarth—inonlythelast10percentofEarth’shistory.Duringageologicallybrief100-million-yearperiod,allmodernanimalgroups(alongwithotheranimalsthatarenowextinct)evolved.Thisrapidoriginanddiversificationofanimalsisoftenreferredtoas“theCambrianexplosion.”Scientistshaveaskedimportantquestionsaboutthisexplosionformorethanacentury.WhydiditoccursolateinthehistoryofEarth?Theoriginofmulticellularformsoflifeseemsarelativelysimplestepcomparedtotheoriginoflifeitself.Whydoesthefossilrecordnottheseriesofevolutionarychangesduringtheevolutionofanimals?Whydidanimallifeevolvesoquickly?Paleontologistscontinuetosearchthefossilrecordforanswerstothesequestions.Oneinterpretationregardingtheabsenceoffossilsduringthisimportant100-million-yearperiodisthatearlyanimalsweresoftbodiedandsimplydidnotfossilize.Fossilizationofsoft-bodiedanimalsislesslikelythanfossilizationofhard-bodiedanimals,butitdoesoccur.Conditionsthatpromotefossilizationofsoft-bodiedanimalsincludeveryrapidcoveringbysedimentsthatcreateanenvironmentthatdiscourages position.Infact,fossilbedscontainingsoft-bodiedanimalshavebeenknownformanyyears.TheEdiacarafossilformation,whichcontainstheoldestknownanimalfossils,consistsexclusivelyofsoft-bodiedforms.AlthoughnamedafterasiteinAustralia,theEdiacaraformationisworldwideindistributionanddatestoPrecambriantimes.This700-million-year-oldformationgivesfewcluestotheoriginsofmodernanimals,however,becausepaleontologistsbelieveitrepresentsanevolutionaryexperimentthatfailed.Itcontainsnoancestorsofmodernanimalgroups.AslightlyyoungerfossilformationcontaininganimalremainsistheTommotianformation,namedafteralocaleinRussia.ItdatestotheveryearlyCambrianperiod,anditalsocontainsonlysoft-bodiedforms.Atonetime,theanimalspresentinthesefossilbedswereassignedtovariousmodernanimalgroups,butmostpaleontologistsnowagreethatallTommotianfossilsrepresentuniquebodyformsthataroseintheearlyCambrianperiodanddisappearedbeforetheendoftheperiod,leavingnodescendantsinmodernanimalAthirdfossilformationcontainingbothsoft-bodiedandhard-bodiedanimalsprovidesevidenceoftheresultoftheCambrianexplosion.Thisfossilformation,calledtheBurgessShale,isinYohoNationalParkintheCanadianRockyMountainsofBritishColumbia.ShortlyaftertheCambrianexplosion,mudslidesrapidlyburiedthousandsofmarineanimalsunderconditionsthatfavoredfossilization.Thesefossilbedsprovideevidenceofabout32modernanimalgroups,plusabout20otheranimalbodyformsthataresodifferentfromanymodernanimalsthattheycannotbeassignedtoanyoneofthemoderngroups.TheseunassignableanimalsincludealargeswimmingpredatorcalledAnomalocarisandasoft-bodiedanimalcalledWiwaxia,whichatedetritusoralgae.TheBurgessShaleformationalsohasfossilsofmanyextinctrepresentativesofmodernanimalgroups.Forexample,awell-knownBurgessShaleanimalcalledSidneyiaisarepresentativeofapreviouslyunknowngroupofarthropods(acategoryofanimalsthatincludesinsects,spiders,mites,andcrabs).FossilformationsliketheBurgessShaleshowthatevolutioncannotalwaysbethoughtofasaslowprogression.TheCambrianexplosioninvolvedrapidevolutionarydiversification,followedbytheextinctionofmanyuniqueanimals.Whywasthisevolutionsorapid?Noonereallyknows.Manyzoologistsbelievethatitwasbecausesomanyecologicalnicheswereavailablewithvirtuallynocompetitionfromexistingspecies.WillzoologistseverknowtheevolutionarysequencesintheCambrianexplosion?Perhapsanotherancientfossilbedofsoft-bodiedanimalsfrom600-million-year-oldseasisawaitingdiscovery.Paragraph1:Thegeologictimescaleismarkedbysignificantgeologicandbiologicalevents,includingtheoriginofEarthabout4.6billionyearsago,theoriginoflifeabout3.5billionyearsago,theoriginofeukaryoticlife-forms(livingthingsthathavecellswithtruenuclei)about1.5billionyearsago,andtheoriginofanimalsabout0.6billionyearsago.ThelasteventmarksthebeginningoftheCambrianperiod.AnimalsoriginatedrelativelylateinthehistoryofEarth—inonlythelast10percentofEarth’shistory.Duringageologicallybrief100-million-yearperiod,allmodernanimalgroups(alongwithotheranimalsthatarenowextinct)evolved.Thisrapidoriginanddiversificationofanimalsisoftenreferredtoas“theCambrianexplosion.”Theword“significant”inthepassageisclosestinmeaningTheword“relatively”inthepassageisclosestinmeaningTheword“diversification”inthepassageisclosestinmeaningemergenceofmanysteadydeclineingradualincreaseinbodysuddenParagraph2:Scientistshaveaskedimportantquestionsaboutthisexplosionformorethanacentury.WhydiditoccursolateinthehistoryofEarth?Theoriginofmulticellularformsoflifeseemsarelativelysimplestepcomparedtotheoriginoflifeitself.Whydoesthefossilrecordnottheseriesofevolutionarychangesduringtheevolutionofanimals?Whydidanimallifeevolvesoquickly?Paleontologistscontinuetosearchthefossilrecordforanswerstothesequestions.Theperioddiscussedinthepassageisreferredtoasan“explosion”becauseoccurred0.6billionyearsago,lateinEarth’swascharacterizedbytheunusuallyfastevolutionofmanynewlife-wascharacterizedbywidespreadanimalwascharacterizedbyviolentvolcanicAccordingtoParagraph2,whichofthefollowingisNOTaquestionthatpaleontologistsaskedabouttheCambrianexplosion?WhywastheoriginoflifeasimplestepinEarth’sWhydidittakesolongformulticellularorganismstoWhydidanimallifeevolvesoWhydoesthefossilrecordlackevidenceofanimalevolutionduringthatWhichofthefollowingbestdescribestherelationshipbetweenparagraph2andparagraph3?Paragraph2putsforwardseveralscientificclaims,oneofwhichisrejectedinparagraph3.Paragraph2posesseveralquestions,andparagraph3offersapossibleanswertooneofthem.Paragraph2presentsoutdatedtraditionalviews,whileparagraph3presentsthecurrentscientificconclusions.Paragraph2introducesageneralizationthatisillustratedbyspecificexamplesinparagraph3.Paragraph3:Oneinterpretationregardingtheabsenceoffossilsduringthisimportant100-million-yearperiodisthatearlyanimalsweresoftbodiedandsimplydidnotfossilize.Fossilizationofsoft-bodiedanimalsislesslikelythanfossilizationofhard-bodiedanimals,butitdoesoccur.Conditionsthatpromotefossilizationofsoft-bodiedanimalsincludeveryrapidcoveringbysedimentsthatcreateanenvironmentthatdiscourages Infact,fossilbedscontainingsoft-bodiedanimalshavebeenknownformanyyears.Theword“promote”inthepassageisclosestinmeaningParagraph4:TheEdiacarafossilformation,whichcontainstheoldestknownanimalfossils,consistsexclusivelyofsoft-bodiedforms.AlthoughnamedafterasiteinAustralia,theEdiacaraformationisworldwideindistributionanddatestoPrecambriantimes.This700-million-year-oldformationgivesfewcluestotheoriginsofmodernanimals,however,becausepaleontologistsbelieveitrepresentsanevolutionaryexperimentthatfailed.Itcontainsnoancestorsofmodernanimalgroups.WhichofthefollowingisNOTmentionedinparagraph4asbeingtrueoftheEdiacaraformation?ItcontainsfossilsthatdatebacktothePrecambrianItcontainsonlysoft-bodiedanimalItislocatedonasinglesiteinItdoesnotcontainanyfossilsoftheancestorsofmodernParagraph5:AslightlyyoungerfossilformationcontaininganimalremainsistheTommotianformation,namedafteralocaleinRussia.ItdatestotheveryearlyCambrianperiod,anditalsocontainsonlysoft-bodiedforms.Atonetime,theanimalspresentinthesefossilbedswereassignedtovariousmodernanimalgroups,butmostpaleontologistsnowagreethatallTommotianfossilsrepresentuniquebodyformsthataroseintheearlyCambrianperiodanddisappearedbeforetheendoftheperiod,leavingnodescendantsinmodernanimalgroups.Whichofthesentencesbelowbestexpressestheessentialinformationinthehighlightedsentenceinthepassage?Incorrectchoiceschangethemeaninginimportantwaysorleaveoutessentialinformation.TheanimalsfoundintheTommotianfossilbedwereoncethoughttobelongtoavarietyofmodernanimalgroups,butnowtheyarethoughttohavedescendedfromasinglegroup.AnimalsintheTommotianfossilbedswereinitiallyassignedtomodernanimalgroupsbutarenowthoughttobelongtogroupsthatemergedanddiedoutduringtheCambrianperiod.Thoughatfirsttheythoughtotherwise,paleontologistsnowagreethattheanimalsintheTommotianhavebodyformsfromwhichmodernanimalshavedescended.ItisunclearwhethertheTommotianfossilsfromtheearlyCambrianperiodrepresentuniquebodyformsorwhethertheyshouldbeassignedtovariousmodernanimalgroups.Paragraph6:Athirdfossilformationcontainingbothsoft-bodiedandhard-animalsprovidesevidenceoftheresultoftheCambrianexplosion.Thisfossilformation,calledtheBurgessShale,isinYohoNationalParkintheCanadianRockyMountainsofBritishColumbia.ShortlyaftertheCambrianexplosion,mudslidesrapidlyburiedthousandsofmarineanimalsunderconditionsthatfavoredfossilization.Thesefossilbedsprovideevidenceofabout32modernanimalgroups,plusabout20otheranimalbodyformsthataresodifferentfromanymodernanimalsthattheycannotbeassignedtoanyoneofthemoderngroups.TheseunassignableanimalsincludealargeswimmingpredatorcalledAnomalocarisandasoft-bodiedanimalcalledWiwaxia,whichatedetritusoralgae.TheBurgessShaleformationalsohasfossilsofmanyextinctrepresentativesofmodernanimalgroups.Forexample,awell-knownBurgessShaleanimalcalledSidneyiaisarepresentativeofapreviouslyunknowngroupofarthropods(acategoryofanimalsthatincludesinsects,spiders,mites,andcrabs).Whydoestheauthormention“Anomalocans”andTocontrastpredatorswithanimalsthateatntssuchasToquestiontheeffectsofrapidmudslidesonTosuggestthatmuchisstillunknownaboutanimalsfoundintheBurgessToprovideexamplesoffossilsthatcannotbeassignedtoamodernanimal“Sidneyia”isanexamplearelativeofAnomalocarisandapreviouslyunknownBurgessShaleanextinctmemberofacurrentlyexistingcategoryofananimalthatcannotbeassignedtoanymodernanimalParagraph7:FossilformationsliketheBurgessShaleshowthatevolutioncannotalwaysbethoughtofasaslowprogression.TheCambrianexplosioninvolvedrapidevolutionarydiversification,followedbytheextinctionofmanyuniqueanimals.Whywasthisevolutionsorapid?Noonereallyknows.Manyzoologistsbelievethatitwasbecausesomanyecologicalnicheswereavailablewithvirtuallynocompetitionfromexistingspecies.WillzoologistseverknowtheevolutionarysequencesintheCambrianexplosion?Perhapsanotherancientfossilbedofsoft-bodiedanimalsfrom600-million-year-oldseasisawaitingdiscovery.Whatcanbeinferredfromparagraph7aboutwhytheCambrianexplosionissoItwasaperiodofrapidevolution,andevolutionisoftenthoughtofasaslowItisaperiodwhoseevolutionarysequencesareclearlyItgeneratedaverylargenumberofancientfossilbedscontainingsoft-bodied100-million-yearperiodisthatearlyanimalsweresoftbodiedandsimplydidnotFossilizationofsoft-bodiedanimalsislesslikelythanfossilizationofhard-bodiedanimals,butitdoesoccur.■Conditionsthatpromotefossilizationofsoft-bodiedanimalsincludeveryrapidcoveringbysedimentsthatcreateanenvironmentthatdiscouragesposition.■Infact,fossilbedscontainingsoft-bodiedanimalshavebeenknownformanyyears.Lookatthefoursquares[■]thatindicatewherethefollowingsentencecouldbeaddedtothepassage.Itisrelativelyrarebecausethefossilizationofsoft-bodiedanimalsrequiresaspecialenvironment.WherecouldthesentencebestDirections:Anintroductorysentenceforabriefsummaryofthepassageisprovidedbelow.CompletethesummarybyselectingtheTHREEanswerchoicesthatexpressthemostimportantideasinthepassage.Someanswerchoicesdonotbelonginthesummarybecausetheyexpressideasthatarenotpresentedinthepassageorareminorideasinthepassage.Thisquestionisworth2points.Theterm“Cambrianexplosion”referstothegeologicallybriefperiodduringwhichmodernanimalgroups●●●AnswerLittleisknownaboutthestagesofevolutionduringtheCambrianper