世界大地构造学五

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.50-55million

yearsagoIndiabegantocollidewithAsiaformingtheTibetanplateauandHimalayas.

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-AtlanticRidgewillbesubductedandthecontinentswillcomeclosertogether.Th三e三ne三xt三P三an三ge三a,三"三Pa三ng三ea三U三lt三im三a"三w三il三l三fo三rm三a三s三a三re三su三lt三o三f三th三e三su三bd三uc三ti三on三o三f三th三e三oc三ea三n三fl三oo三r三of三t三he三N三or三th三a三nd三S三ou三th三A三tl三an三ti三c三be三ne三at三h三ea三