世界大地构造学5

Thismapillustratesthe

break-upofthesupercontinent,Rodinia,whichformed1100millionyearsago.

TheLatePrecambrianwas

an"IceHouse"World,muchlikethepresent-day.Animalswithhard-shellsappearedingreatnumbersforthefirsttimeduringtheCambrian.

Thecontinentswerefloodedbyshallowseas.

ThesupercontinentofGondwanahadjustformedandwaslocatedneartheSouthPole.DuringtheOrdovicianancientoceansseparatedthebarrencontinentsofLaurentia,Baltica,SiberiaandGondwana.

TheendoftheOrdovicianwasoneofthecoldesttimesinEarthhistory.

IcecoveredmuchofthesouthernregionofGondwana.LaurentiacollideswithBalticaclosingthenorthenbranchoftheIapetusOceanandformingthe"OldRedSandstone"continent.

Coralreefsexpandandlandplantsbegintocolonizethebarrencontinents.BytheDevoniantheearlyPaleozoicoceanswereclosing,forminga"pre-Pangea".

FreshwaterfishwereabletomigratefromthesouthernhemispherecontinentstoNorthAmericaandEurope.

ForestsgrewforthefirsttimeintheequatorialregionsofArticCanada.DuringtheEarlyCarboniferousthePaleozoicoceansbetweenEuramericaandGondwanabegantoclose,formingtheAppalachianandVariscanmountains.

AnicecapgrewattheSouthPoleasfour-leggedvertebratesevolvedinthecoalswampsneartheEquator.DuringtheEarlyCarboniferousPangeaBeginstoForm.BytheLateCarboniferousthecontinentsthatmakeupmodernNorthAmericaandEuropehadcollidedwiththesoutherncontinentsofGondwanatoform

thewesternhalfofPangea.

Icecoveredmuchofthesouthernhemisphereandvastcoalswampsformedalongtheequator.Vast

desertscoveredwesternPangeaduringthePermianasreptilesspreadacrossthefaceofthesupercontinent.

99%ofalllifeperishedduringtheextinctioneventthatmarkedtheendofthePaleozoicEra.ThesupercontinentofPangea,mostlyassembledbytheTriassic,allowedlandanimalstomigratefromtheSouthPoletotheNorthPole.

LifebegantorediversifyafterthegreatPermo-Triassicextinctionandwarm-waterfaunasspreadacrossTethys.BytheEarlyJurassic,south-centralAsiahadassembled.

AwideTethysoceanseparatedthenortherncontinentsfromGondwana.

ThoughPangeawasintact,thefirstrumblingsofcontinentalbreakupcouldbeheard.ThesupercontinentofPangeabegantobreakapartintheMiddleJurassic.IntheLateJurassictheCentralAtlanticOceanwasanarrowoceanseparatingAfricafromeasternNorthAmerica.EasternGondwanahadbeguntoseparateformWesternGondwana.DuringtheCretaceoustheSouthAtlanticOceanopened.IndiaseparatedfromMadagascarandracednorthwardonacollisioncoursewithEurasia.NoticethatNorthAmericawasconnectedtoEurope,andthatAustraliawasstilljoinedtoAntarctica.Thebull'seyemarksthelocationoftheChicxulubimpactsite.Theimpactofa10milewidecometcausedglobalclimatechangesthatkilledthedinosaursandmanyotherformsoflife.BytheLateCretaceoustheoceanshadwidened,andIndiaapproachedthesouthernmarginofAsia.50-55millionyearsagoIndiabegantocollidewithAsiaformingtheTibetanplateauandHimalayas.Australia,whichwasattachedtoAntarctica,begantomoverapidlynorthward.20millionyearsago,Antarcticawascoverdbyiceandthenortherncontinentswerecoolingrapidly.Theworldhastakenona"modern"look,butnoticethatFloridaandpartsofAsiawerefloodedbythesea.WhentheEarthisinits"IceHouse"climatemode,thereisiceatthepoles.ThepolaricesheetexpandsandcontactsbecauseofvariationsintheEarth'sorbit(Milankovitchcycles).Thelastexpansionofthepolaricesheetstookplaceabout18,000yearsago.WeareenteringanewphaseofcontinentalcollisionthatwillultimatelyresultintheformationofanewPangeasupercontinentinthefuture.GlobalclimateiswarmingbecauseweareleavinganIceAgeandbecauseweareaddinggreenhousegasestotheatmosphere.Ifwecontinuepresent-dayplatemotionstheAtlanticwillwiden,AfricawillcollidewithEuropeclosingtheMediterranean,AustraliawillcollidewithS.E.Asia,andCaliforniawillslidenorthwardupthecoasttoAlaska.NewsubductionzonesalongtheeasterncoastsofNorthAmericaandSouthAmericawillbegintoconsumetheoceanfloorseparatingNorthAmericafromAfrica.About100millionyearsfromnowthepresent-dayMid-AtlanticRidgewillbesubductedandthecontinentswillcomeclos