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Intheearly20thcentury,GermanscientistAlfredWegenerpublishedabookexplaininghistheorythatthe
continentallandmasses,farfrombeingimmovable,weredriftingacrosstheEarth.Hecalledthismovement
continentaldrift.
WegenernoticedthatthecoastsofwesternAfricaandeasternSouthAmericalookedliketheedgesofinterlocking
piecesofajigsawpuzzle.Hewasnotthefirsttonoticethis,buthewasthefirsttoformallypresentevidence
suggestingthatthetwocontinentshadoncebeenconnected.
Wegenerwasconvincedthatthetwocontinentswereoncepartofanenormous,singlelandmassthathadsplit
apart.Heknewthatthetwoareashadmanygeologicalandbiologicalsimilarities.Forexample,fossilsofthe
ancientreptilemesosaurusareonlyfoundinsouthernAfricaandSouthAmerica.Mesosaurus,afreshwaterreptile
onlyonemeter(3.3feet)long,couldnothaveswumtheAtlanticOcean.Thepresenceofmesosaurussuggestsa
singlehabitatwithmanylakesandrivers.
Wegenerbelievedthatallthecontinents—notjustAfricaandSouthAmerica—hadoncebeenjoinedinasingle
supercontinent.ThishugeancientlandmassisknownasPangaea,whichmeans“alllands”inGreek.Pangaea
existedabout240millionyearsago.Byabout200millionyearsago,thissupercontinentbeganbreakingup.Over
millionsofyears,Pangaeaseparatedintopiecesthatmovedawayfromoneanother.Thesepiecesslowly
assumedtheirpresentpositionsasthecontinents.
TectonicActivity
Atfirst,otherscientistsdidnotacceptWegener’stheoryofcontinentaldrift.Butscientistsnowknowthatthe
continentsrestonmassiveslabsofrockcalledtectonicplates.Theplatesarealwaysmovingandinteractingina
processcalledplatetectonics.Overtime,tectonicactivitychangestheEarth’ssurface,rearrangingandreshaping
itslandmasses.
Today,scientistsbelievethatseveralsupercontinentslikePangaeahaveformedandbrokenupoverthecourseof
theEarth’slifespan.TheseincludePannotia,whichformedabout600millionyearsago,andRodinia,whichexisted
morethanabillionyearsago.
Thecontinentsarestillmovingtoday.Underwaterexplorationhasrevealedseafloorspreading.Seafloorspreading
istheprocessofnewcrustformingbetweentwoplatesthataremovingapart.Alonganetworkofmountainranges
intheocean,moltenrockrisesfromwithintheEarthandaddsnewseafloortotheedgesoftheold.Astheseafloor
growswider,thecontinentsonoppositesidesoftheridgesmoveawayfromeachother.
NorthAmericaandEurope,forexample,aremovingawayfromeachotherattherateofabout2.5centimeters(1
inch)peryear.Ifyoucouldvisittheplanetinthefuture,youmightfindpartofCaliforniaseparatedfromNorth
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America,becominganislandinthePacificOcean.AfricawilleventuallysplitintwoalongtheGreatRiftValley.Itis
evenpossiblethatanothersupercontinentmayformsomeday.
VOCABULARY
Term
PartofSpeech
Definition
AlfredWegener
noun
(1880-1930)Germanmeteorologistandgeologist.
ancient
adjective
veryold.
biological
adjective
havingtodowiththestudyoflifeandlivingorganisms.
coast
noun
edgeoflandalongtheseaorotherlargebodyofwater.
continent
noun
oneofthesevenmainlandmassesonEarth.
continentaldrift
noun
themovementofcontinentsresultingfromthemotionoftectonicplates.
crust
noun
rockyoutermostlayerofEarthorotherplanet.
fossil
noun
remnant,impression,ortraceofanancientorganism.
geologic
adjective
havingtodowiththephysicalformationsoftheEarth.
GreatRiftValley
system
noun
seriesoffaultsandothersitesoftectonicactivitystretchingfromsouthwestern
AsiatotheHornofAfrica.
habitat
noun
environmentwhereanorganismlivesthroughouttheyearorforshorterperiods
oftime.
immovable
adjective
unabletochangepositionormove.
island
noun
bodyoflandsurroundedbywater.
jigsawpuzzle
noun
interlockingpiecesthat,whencorrectlyputtogether,displayapictureordesign.
landmass
noun
largeareaofland.
mesosaurus
noun
freshwaterreptilethatlivedduringtheearlyPermianperiod,about300million
yearsago.
molten
adjective
solidmaterialturnedtoliquidbyheat.
mountainrange
noun
seriesorchainofmountainsthatareclosetogether.
Pangaea
noun
supercontinentofalltheEarth'slandmassthatexistedabout250millionyears
ago.
Pannotia
noun
supercontinentthatexistedabout600millionyearsago.
platetectonics
noun
movementandinteractionoftheEarth'splates.
reptile
noun
animalthatbreathesairandusuallyhasscales.
revolutionary
adjective
neworinnovative.
riftvalley
noun
depressioninthegroundcausedbytheEarth'scrustspreadingapart.
Rodinia
noun
supercontinentthatexistedaboutabillionyearsago.
seafloorspreading
noun
riftinunderwatermountainrangewherenewoceaniccrustisformed.
supercontinent
noun
ancient,giantlandmassthatsplitaparttoformallthecontinentsweknowtoday.
tectonicplate
noun
large,moveablesegmentoftheEarth'scrust.
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FORFURTHEREXPLORATION
Audio&Video
UniversityofCalifornia:MuseumofPaleontology—ContinentalDrift
Interactives
NASA:PangaeaInteractiveMapGame
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