Aurora from the ISSCourse AnnouncementsAssignmentsSurface Features - Plate TectonicsPlate TectonicsPlate Tectonic MotionPlate Tectonic MotionPlate Tectonic MotionPlate Tectonic MotionPlate TectonicsPlate TectonicsPlate Tectonic MotionPangaeaReshaping LandmassesEarth’s Magnetic FieldEarth’s Magnetic FieldEarth’s MagnetosphereEarth’s MagnetosphereEarth’s MagnetosphereAuroraEarth’s TidesEarth’s TidesThe Tidal ForceEarth’s TidesEarth’s TidesEarth’s TidesEarth’s TidesTidal LockingTidal LockingTidal LockingTidal LockingThe Synchronous Orbit of the MoonLunar LibrationThe Synchronous Orbit of the MoonThe Synchronous Orbit of the MoonThe Synchronous Orbit of the MoonThe Synchronous Orbit of the MoonAurora from the ISSImage Credit: Scott Kelly/NASACourse Announcements•Thanksgiving Week planningNo classes Wednesday, 23 Nov.Upcoming Schedule•Quiz 4: Today•Exam 2: Friday, 28 October–Chapters 5, 6, 7, Dr. Lindsay’s Custom Material, parts of Ch. 8. [wherever I get to on Wed.]–Study session next week: Thursday at 6pm in Room 304 of Nielsen Physics and Astronomy–MA study guide, “Must Knows”, and Chapter slides coming as soon as I get them prepared for youAssignmentsReading Assignments•Chapter 8: 8.5 – 8.8[Read by exam on Friday, 28 Oct.]Parallel Lectures•CC Astronomy – Episode 12: The Moon[Watch before exam Friday, 28 Oct.]Mastering Astronomy•Chapter 7 Homework[Due Monday, 21 October at 11:59 PM EDT]Surface Features - Plate Tectonics•The surface features of the Earth are dominated by plate tectonics, in which the oceans and continents are floating on top of a convective mantle in a series of connected plates.–All the plates fit together like a global jigsaw puzzle–These plates are all moving around causing changes in the shape of Earth’s crust [tectonics]–Two types of plates:Oceanic plates Continental plates•Earth appears is unique in that it still has active plate tectonics.Continental DrifPlate TectonicsPlate BoundariesHigh levels of volcanic activity occur at plate boundaries.Comparative Planetology Question: Do other planets show similar patterns?Red dots indicate volcanoesWhite arrows show plate movementBlue lines indicate plate boundariesPlate Tectonic MotionAfloat on a sea of a convective mantle•Plate tectonic motion associated with convection cells in the mantle•Note that this is the second of three parts of the Earth where convection is occurring and driving significant Earth processesPlate Tectonic MotionOne plate slides under another-Subduction ZoneHimalayas with Mt. Everest on the rightIndian plate pushing northward and sliding under (subducting) the Eurasian plate. As one plate slides under the other, mountains are pushed up and formedPlate Tectonic MotionSliding past each other formingfaultsThe San Andreas Fault in California. The Pacific plate is drifting Northwest relative to the North American plate.Lots of energy released when movement along fault occurs generating potentially very powerful earthquakes.Plate Tectonic MotionSpreading platesMid-Atlantic RidgeAs the ocean floor spreads, and new crust is formed, the rocks preserve the orientation of Earth’s magnetic field. These rocks show that the polarity (N – S) orientation flips on average about every ½ million yearsPlate Tectonics•Taken together, the Earth’s plates make up the lithosphere.–Literally means, sphere (realm) of rocks•The lithosphere makes up the Earth’s crust and upper, solid mantle. –It is roughly 100 km thick on average•The plates of the lithosphere slide on top of part of the convective mantle and lower crust. This part of the is called the asthenosphere, which is not molten but it is highly viscous (can flow).–The plates are moving! The features of Earth’s surface are changing (very slowly). So, called continental drif due to plate tectonic motionThe parts that make it workPlate TectonicsThe parts that make it workPlate Tectonic MotionAfloat on a sea of a convective mantle•Plate tectonic motion associated with convection cells in the mantle•Magma will seep to surface at cracks in plate boundaries–Volcanoes are much more prevalent at these boundaries (explains the “Ring of Fire” and the previous figure of volcano locations)•Plates can collide with each other, spread away from each other, or grind/shear/slide past one-another–Each forming its own geologic features, e.g., mountain chains, rift valleys, uplifts (like the Tibetan plateau), etc.–i.e., shaping the the part of the Earth we live on (the crust)Pangaea•Plate tectonic motion moves the continents with drift of about at about 2 cm per year•Can trace the current continental drifts backwards, to find that all the landmasses were gathered into one Supercontinent, called Pangaea, about 200 million years ago–Explains a lot of the geographic disjuncture in the fossil record–Most likely a recurring landmass pattern. There were and will be several more Pangaeas.The Supercontinent of 200 million years agoReshaping LandmassesContinental DrifCredit: Müller et al. (2008)Plate motion reshapes the surface of the Earth.This animation demonstrates how landmasses (and ocean floors) have shifted over the past 140 Million YearsEarth’s Magnetic FieldDoes it fit the dynamo effect requirements?•Rotational Period less than 10s of days? 23 hr 56 minutes - Check•Conductive liquid in interior that is convecting?Molten liquid outer metallic core made of iron and nickel that experiences convection- Check•We expect Earth to have a significant magnetic field!- And it does! CheckEarth’s Magnetic FieldLike a planet-sized bar magnetZoomed in, looks like a bar magnetField lines come out of South (S) and go into North (N)Zoomed out, the Solar Wind compresses the field on the Sunward side, and drags out (like water around a rock in a river) the side away from the Sun creating a tailEarth’s MagnetosphereRegion influenced by Earth’s magnetic fieldEarth’s Magnetosphere: Region around Earth dominated by Earth’s Magnetic FieldEarth’s Magnetosphere•Strength of Magnetic Field at Earth’s surface: 25 – 65 microtelsa (or 0.25 – 0.65 Gauss)•The charged particles of the solar wind are deflected by Earth’s magnetic field–Particles with electric charges feel a force in a magnetic field.–Will spiral around magnetic field lines–Protects our atmosphere from being stripped away by the solar wind•Certain areas of magnetosphere perfect for trapping
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