Slide 1EarthSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42PYTS/ASTR 206 – Earth1AnnouncementsLate HW3s due now 50% late creditThursday office hours?No one was concernedWe’ll drop this slot – email me for a time to meet insteadDrop day is todayCalculate your expected grade…Add HW1 and HW2 percentages together, multiply by 0.15Add the two in-class activity marks (out of 5) together, multiply by 2Take your mid-term score (out of 45), multiply by 1.111Add these three things together…. And compare to grade tableThis is a REALLY rough guess, you can easily move up/down a gradePYTS/ASTR 206 – Earth2PTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected]/ASTR 206 – Earth3In this lecture…In this lecture…Introduction to the EarthRecap on InteriorTwo types of crustOceanic crustContinental crustPlate TectonicsCurrent platesEvidence for plate tectonicsPlate motionSpreading centers and subductionHistory of plate motionsEarly EarthBuilding continentsEarly atmosphereForming the oceansLifeWhen it formedRise of OxygenPYTS/ASTR 206 – Earth4What’s unique about the Earth?Impact craters? – NoVolcanoes? – NoPYTS/ASTR 206 – Earth5What’s unique about the Earth?Fluvial erosion? – NoRivers? – NoPYTS/ASTR 206 – Earth6What’s unique about the Earth?Glaciers? – NoTectonics? – NoPYTS/ASTR 206 – Earth7What’s unique about the Earth?Wind action? – NoSo what is unique about the Earth?PYTS/ASTR 206 – Earth8What’s unique about the Earth?Two main things to talk about in this lecture…Plate Tectonics LifePYTS/ASTR 206 – Earth9Rocky planets have several partsCore – Iron/NickelMantle – RockyCrust – Rocky (different composition)Strong rocks near surfaceColder rocks = stronger rocksLithosphereRocks are brittleWeak rocks deeperHotter rocks = weaker rocksAsthenosphereRocks flowCoreSolid in center – inner coreSurrounded by liquid iron – outer core Recap interior…Recap interior…PYTS/ASTR 206 – Earth10Compositional vs mechanical termsCrust, mantle, core are compositionally differentLithosphere, Asthenosphere, Mesosphere, Outer Core and Inner Core are mechanically different Lithosphere is divided into plates…PYTS/ASTR 206 – Earth11Hotter interior temperatures cause convection in the mantleShijie Zhong, U. ColoradoPYTS/ASTR 206 – Earth12Convection causes meltingMelting point depends on pressureMaterial rises to lower pressure zonePreviously solid, but can now partly meltPartly molten zoneCalled ‘asthenosphere’Able to flowPYTS/ASTR 206 – Earth13LithosphereBrittle upper layerCan move around on plastic asthenosphereDivided into many plates1000-10000 km acrossMost plates contain both continental and oceanic crustPYTS/ASTR 206 – Earth14Crust is a compositional distinctionMost rock is in the mantleMixture of two main minerals Olivine and PyroxeneEarth has two types of crustOceanic crust – low-lying Continental crust – high-standing Oceans cover oceanic crust and some of the continental crustHow do we manufacture this crust?Through volcanic activityTwo types of crustTwo types of crustPYTS/ASTR 206 – Earth15Oceans cover oceanic crust and some of the continental crustNot always the caseMore continental crust exposed during the last ice age when sea levels droppedOceaniccrustContinental crustPYTS/ASTR 206 – Earth16Oceanic and continental crust comparedOceanic ContinentalDensity 3000 kg m-32700 kg m-3Thickness 5km 20-100kmComposition Basalt GraniteAge <0.1 billion years > 1 billion yearsOceanMantleOceanic crustContinen-tal crustPYTS/ASTR 206 – Earth17These large plates are constantly movingMost plate move at centimeters/year – like growing fingernails…Measured with GPS and Very Long Baseline InterferometeryPlate TectonicsPlate TectonicsPYTS/ASTR 206 – Earth18Plates move around from…Convection currentsPull of sinking slabsStill not totally understoodShijie Zhong, U. ColoradoPYTS/ASTR 206 – Earth19Old evidence for plate tectonics…Similar fossils in locations that are widely separated todayContinental shapes fit together like a jigsawMatching rock typesPlate tectonics was already a theory before modern instruments confirmed itPYTS/ASTR 206 – Earth20More-recent evidence for plate tectonics…Seafloor surveys revealed mid-ocean spreading ridges Magnetic reversals across ridgesLocations of earthquakes and volcanoesPacific ring of firePYTS/ASTR 206 – Earth21When plates separate…New oceanic crustPartial melting of mantle materialCharacteristic stratigraphic sequence:Gabbro(large grained basalt)Sheeted dikesEach sheet was the wall of the inner ridgePillow basaltsBlobs of basalt that are quickly quenchedOcean sedimentsFine-grained mudsPillow BasaltPYTS/ASTR 206 – Earth22Magnetic reversals match across spreading ridgesEarth’s magnetic field switches north and south pole every so oftenNew rock gets magnetized before it coolsMagnetic record is preservedSame pattern on each side of the spreading ridgePress & Siever, 2nd editionPYTS/ASTR 206 – Earth23Crust moves away from spreading centersCrust near the spreading centers is still youngPYTS/ASTR 206 – Earth24What happens when plates collide?All depends on densityOceanic crust has a higher density than the continentsThree possible collisionsOcean-continent South America and the Nazca plateOcean-oceanWest pacific regionContinent-continentIndia collides with EurasiaOceanMantleOceanic crustContinen-tal crustPress & Siever, 2nd editionPYTS/ASTR 206 – Earth25A continent-ocean plate collisionWest of South-AmericaOcean plate is denser Continent ends up on topOcean plate ‘subducts’Ocean-plate drags down water which lowers the melting point of rocks Lots of volcanoes…but these volcanoes spew out reprocessed oceanic crust (not mantle
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