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1.andesite:anintermediatetypeofvolcanicrockbetweenbasaltandrhyolite.2.back-arcbasic:aseafloorspreadingsystemofvolcanoescausedextensionbehindanislandarcthatisaboveasubductionzone.3.barrierisland:alow,elongatedcoastalislandthatparallelstheshorelineandprotectsthebeachfromstorms.4.basalt:adark,volcanicrockrichinironandmagnesiumandusuallyquitefluidinthemoltenstate.5.carbonate:amineralcontainingcalciumcarbonatesuchaslimestoneanddolostone.6.Cenozoic:aneraofgeologictimecomprisingthelast65millionyears.7.Circum-Pacificbelt:activeseismicregionsaroundtherimofthebeltPacificplatecoincidingwiththeRingofFire.8.continentaldrift:theconceptthatthecontinentsdriftacrossthesurfaceofEarth.9.continentalshelf:theoffshoreareaofacontinentinshallowsea.10.continentalslope:thetransitionfromthecontinentalshelftothedeep-seabasin.11.ConvergentPlatemargin:theboundarybetweencrustalplateswheretheplatescometogether;generallycorrespondstothedeep-seatrencheswhereoldcrustisdestroyedinsubductionzones.12.delta:thewedge-shapedpileofsedimentsdepositedatthemouthofariver.13.divergentplatemargin:theboundarybetweenlithosphericplateswheretheyseparate;itgenerallycorrespondstomidoceanridgeswherenewcrustisformedbythesolidificationofliquidrockrisingfrombelow.14.erosion:thewearingawayofsurfacematerialsbynaturalagentssuchaswindandwater.15.fossil:anyremains,impressions,ortracesinrockofaplantoranimalofapreviousgeologicage.16.geologiccolumn:thetotalthicknessofgeologicunitsinaregion.17.granite:acoarse-grain,silica-richrockconsistingprimarilyofquartzandfeldspars.18.guyot:underseavolcanothatonceexistedabovesealevelandwhosetopwasflattenedbyerosion;later,subsidencecausedthevolcanotosinkbelowtheoceansurface,preservingitsflat-topappearance.19.hydrocarbon:amoleculeconsistingofcarbonchainswithattachedhydrogenatoms.20.igneousrocks:allrockssolidifiedfromamoltenstate.21.islandarc:volcanoeslandwardofasubductionzone,paralleltoatrenchofasubductingplateandabovetheplate’smeltingzone.22.lava:moltenmagmathatflowsoutontothesurface.23.limestone:asedimentaryrockcomposedofcalciumcarbonatethatissecretedfromseawaterbyinvertebratesandwhoseskeletonscomposethebulkofdeposits.24.lithosphericplate:asegmentofthelithosphere,theupper-layerplateofthemantle,involvedintheinteractionofotherplatesintectonicactivity.25.magma:amoltenrockmaterialgeneratedwithnEarthandthatistheconstituentofigneousrocks.26.midoceanridge:asubmarineridgealongadivergentplateboundarywhereanewoceanflooriscreatedbytheupwellingofmantlematerial.27.RingofFire:abeltofsubductionzonesaroundthePacificplaterelatedtovolcanicactivity.28.seafloorspreading:atheorythattheoceanflooriscreatedbytheseparationoflithosphericplatesalongmidoceanridges,withnewoceaniccrust-formedfrommantlematerialthatrisesfromthemantletofilltherift.29.seamount:asubmarinevolcanothatneverreachesthesurfaceofthesea.30.sedimentation:thedepositionofsediments.31.subductionzone:aregionwhereanoceanicplatedivesbelowacontinentalplateintothemantle;oceantrenchesarethesurfaceexpressionofasubductionzone.32.tectonicactivity:theformationofEarth’scrustbylarge-scalemovementsthroughoutgeologictime.33.transformfault:afractureinEarth’scrustalongwhichlateralmovementoccurs;acommonfeatureofthemidoceanridgescreatedinthelineofseafloorspreading.34.trench:adepressionontheoceanfloorcausedbyplatesubduction.35.turbidite:aslurryofmudthatperiodicallyslidesdownoftengentleslopestowardthedeep-seafloor.1.Theplatetectonicsmodel.Newoceaniccrustisgeneratedatspreadingridges,andoldoceaniccrustisdestroyedinsubductionzones,whichmovesthecontinentsaroundEarth.Thediscoveryofmanymysteriesontheseabed,includingspreadingridgesanddeep-seatrenches,ledgeologiststodevelopanentirelynewwayoflookingatEarth,calledthetheoryofplatetectonics(fig1).TectonicsisthegeologicprocessresponsibleforfeaturesonEarth’ssurface.Thetheoryincorporatedtheprocessofsea-floorspreadingandcontinentaldriftintoacomprehensivemodel.TheAtlanticOceanisbisectedbytheMid-AtlanticRidge,whichmanufacturesnewoceaniccrustasthecontinentssurroundingtheAtlanticbasinspreadapart.TheMid-AtlanticRidgeisthecenterofintenseseismicandvolcanicactivity.ItisthefocusofhighheatflowfromEarth’sinterior.Moltenmagmaoriginatingfromthemantlerisesthroughthelithosphereanderuptsontotheoceanfloor,addingnewoceaniccrusttobothsidesoftheridgecrest.2.(Theoceaniccrustcomprisesatoplayerofpillowbasalts,asecondlayerofsheeteddikes,athirdlayerofgabbros,andanunderlyinglayeroflayeredperidititiesabovethemantle)Oceaniccrustdoesnotfromasasinglehomogeneousmass.Instead,itcompriseslong,narrowribbonslaidsidebysidewithfracturezonesinbetween.Theoceaniccrustiscomparabletoalayercakewithfourdistinctstrata.Theupperlayerispillowbasalts,formedwhenlavaextrudedunderseaatgreatdepths.Thesecondlayerisofasheeted-dikecomplex,consistingofatangledmassoffeedersthatbroughtmagmatothesurface.Thethirdlayerisofgabbros,whicharecoarse-grainedrocksthatcrystallizedslowlyunderhighpressureinadeepmagmachamber.Thefourthlayerisofperidotitessegregatedfromthemantlebelow.Gabbroscontaininghigheramountsofsilicasolidifyoutofthebasalticmeltandaccumu