““OK, so whatOK, so what’’s the speed of dark?s the speed of dark?””““When everything is coming your way,When everything is coming your way,you're obviously in the wrong laneyou're obviously in the wrong lane””““Who laughs last,Who laughs last,thinks slowestthinks slowest””OCNG 251: OceanographyOCNG 251: OceanographyTuesdayTuesday,, Nov. 11 Nov. 11thth, 2008, 2008Defining Boundaries: 2) Plate Tectonics IIDefining Boundaries: 2) Plate Tectonics II1.1.ReviewReview2.2.Plate Tectonics: The dynamic EarthPlate Tectonics: The dynamic EarthDefining BoundariesDefining Boundaries11) Marine Provinces) Marine Provinces2) Intro to Plate Tectonics2) Intro to Plate Tectonics1.1.Marine ProvincesMarine Provinces––Continental Margins (Continental Margins (Shelf, Slope, RiseShelf, Slope, Rise))––Deep-Ocean Basins (Deep-Ocean Basins (Abyssal Plains, AbyssalAbyssal Plains, AbyssalHills, Seamounts, TrenchesHills, Seamounts, Trenches))––Mid-Oceanic RidgesMid-Oceanic Ridges2.2.Intro to Plate TectonicsIntro to Plate Tectonics––Differentiation and formation of distinctDifferentiation and formation of distinctlayerslayers––IsostasyIsostasy (Ocean (Ocean vsvs. Continental Crust). Continental Crust)––Continental Drift and Sea Floor SpreadingContinental Drift and Sea Floor Spreading––EvidenceEvidence……An Introduction to Plate TectonicsAn Introduction to Plate TectonicsOriginallyOriginally, the, theelementselementssegregated duringsegregated duringthe formation ofthe formation ofEarth (densityEarth (density““fractionationfractionation””)) !! Differentiation Differentiationand formation ofand formation ofdistinct layersdistinct layersseemed to haveseemed to havetaken very littletaken very littletime 100Mytime 100MyCrustCrust 0.4% 0.4%(Al, Si, O)(Al, Si, O)CoreCore 31.5% (Ni, 31.5% (Ni,Fe)Fe)MantleMantle 68.1% 68.1%(Mg, Fe, Si, O)(Mg, Fe, Si, O)Physical differentiation?The movements of liquid metalThe movements of liquid metalin the outer core (eddies)in the outer core (eddies)generate a process akin to agenerate a process akin to adynamo that generates adynamo that generates amagnetic field on Earth (andmagnetic field on Earth (andreversalsreversals……))Not all of the core is moltenNot all of the core is moltenAs Pressure As Pressure "", melting point , melting point ""(at higher internal pressures,(at higher internal pressures,Fe melts at >2000Fe melts at >2000°°C)C)So So ““liquidliquid”” iron only occurs iron only occurswhere temperatures are highwhere temperatures are highenough but pressures are lowenough but pressures are lowenoughenoughBut what does it mean to have a liquid core?As the result of the EarthAs the result of the Earth’’ssrotation, the molten iron flowsrotation, the molten iron flowscontinually around the solid innercontinually around the solid innercore core !! forming a forming a magnetic fieldmagnetic fieldAnd how does that change our lives?-- First of First of all, all, it protects us from solar windsit protects us from solar winds……-- But then it provides evidence for differentiation andBut then it provides evidence for differentiation andmolten coremolten core-- Also provides evidence for Also provides evidence for Plate TectonicsPlate TectonicsWhat does it mean to have a plastic Mantle?Principle of IsostasyItIt’’s a matter of balances a matter of balanceOcean Crust vs. Continental Crust….Continental DriftContinental Drift##Alfred WegenerAlfred Wegener (1880-1930), German meteorologist,(1880-1930), German meteorologist,advocated the theory of continental drift in the earlyadvocated the theory of continental drift in the earlyXXXXthth Century. Century.##Drawing on several lines of evidence, he rejuvenated theDrawing on several lines of evidence, he rejuvenated theidea that all the continents were once joined as oneidea that all the continents were once joined as onelandmass, which he named landmass, which he named PangaeaPangaea..Continental DriftContinental Drift##He further proposed that this ancestral supercontinent hadHe further proposed that this ancestral supercontinent hadbegun breaking up approximately 200 million years earlier intobegun breaking up approximately 200 million years earlier intoa northern portion and a southern portion.a northern portion and a southern portion.##He noted that land fossils >150 Ma from different continentsHe noted that land fossils >150 Ma from different continentswere similar, whereas fossils <150 Ma were different and hadwere similar, whereas fossils <150 Ma were different and hadevolved separatelyevolved separatelyContinental DriftContinental Drift##However, the mechanisms he proposed (rotation ofHowever, the mechanisms he proposed (rotation ofthe Earth and tidal forces) did not stand the test ofthe Earth and tidal forces) did not stand the test ofscience and his science and his ““theorytheory”” was disregarded! was disregarded!Evidence for Sea-Floor SpreadingEvidence for Sea-Floor Spreading##In the 1950s, as people began creating detailed maps ofIn the 1950s, as people began creating detailed maps ofthe world's ocean floor, they discovered a mid-ocean ridgethe world's ocean floor, they discovered a mid-ocean ridgesystem of mountains nearly 60,000 km (nearly 40,000 mi)system of mountains nearly 60,000 km (nearly 40,000 mi)long. This ridge goes all the way around the globe.long. This ridge goes all the way around the globe.Sea-floor spreading andSea-floor spreading andPlate TectonicsPlate Tectonics##New material is brought to the surface in the centerNew material is brought to the surface in the centerof Mid-Oceanic ridges (of Mid-Oceanic ridges (Divergent boundariesDivergent boundaries))However, Global Plate TectonicsHowever, Global Plate TectonicsA matter of balance!A matter of balance!How?How?!!Old material sinks below the surface at subductionOld material sinks below the surface at subductionzones (zones (Convergent boundariesConvergent boundaries))Evidence for Sea-Floor SpreadingEvidence for Sea-Floor Spreading##American geologist Harry H. Hess proposed that this mountainAmerican geologist Harry H. Hess proposed that this mountainchain was the place where new ocean floor was created and thatchain was the place where new ocean floor was created and thatthe continents moved as a result of the expansion of the oceanthe continents moved as a result of the expansion of the oceanfloors.floors.##Also during the 1950s, physicists in