Aurora from the ISS Image Credit Scott Kelly NASA Course Announcements Thanksgiving Week planning No 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 you Assignments Reading 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 Continental Drif 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 Plate Tectonics Plate Boundaries Red dots indicate volcanoes White arrows show plate movement Blue lines indicate plate boundaries High levels of volcanic activity occur at plate boundaries Comparative Planetology Question Do other planets show similar patterns Plate Tectonic Motion Afloat 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 processes Plate Tectonic Motion One plate slides under anotherSubduction Zone Indian plate pushing northward and sliding under subducting the Eurasian plate As one plate slides under the other mountains are pushed up and formed Himalayas with Mt Everest on the right Plate Tectonic Motion Sliding past each other forming faults The 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 Motion Spreading plates Mid Atlantic Ridge As 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 million years Plate Tectonics The parts that make it work 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 motion Plate Tectonics The parts that make it work Plate Tectonic Motion Afloat 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 The Supercontinent of 200 million years ago 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 Reshaping Landmasses Continental Drif Plate motion reshapes the surface of the Earth This animation demonstrates how landmasses and ocean floors have shifted over the past 140 Million Years Credit M ller et al 2008 Earth s Magnetic Field Does 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 Check Earth s Magnetic Field Like a planet sized bar magnet Zoomed in looks like a bar magnet Field 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 tail Earth s Magnetosphere Region influenced by Earth s magnetic field Earth s Magnetosphere Region around Earth dominated by Earth s Magnetic Field Earth s Magnetosphere Region influenced by Earth s magnetic field 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 these charged particles They are called the Van Allen belts Earth s Magnetosphere Van Allen Radiation Belts Van Allen belts trap charged particles into two donut shaped rings around the Earth above the ionosphere Inner and Outer Van Allen belts The charged particles mostly electrons and protons will spiral around magnetic field lines and enter the atmosphere near the magnetic poles of Earth Charged particles ionized atmospheric molecules creating the aurorae or lights Northern Aurora Borealis Southern Aurora Australis Van Allen Belts Aurora Aurora Borealis The Northern Lights Credit Bj rn J rgensen Credit David Necchi Earth s Tides The Tidal Force is a differential force Earth s tides are caused by the tidal force which is a differential force due to the gravitational force being weaker at a distance inverse square law Moon s pull on Earth is stronger on the near side than on the farside
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