1Class 17The Planet Earth Structure of the Earth’s interior The Earth’s crust and plate tectonics Structure and changes in Earth’satmosphere The MagnetosphereI : Structure of the interior Basic structure… Solid iron inner core (radius 1300km) Liquid iron outer core (radius 3500km) Solid/plastic mantle (radius 6343km) Solid Crust (just outer 5-35km) Why is this? Earth was build by collisions… started hot and molten While molten, differentiation occurred wherebydense materials (iron) sunk to the center In addition to retaining some of the original heat,radioactivity helps keep interior hot Structure determined by the radial variations intemperature and melting point (which depends onpressure)23 How do we know this? Study seismic waves generated byEarthquakes P-waves Longitudinal (pressure) waves Can travel through solid and liquids S-waves Transverse (shear) waves Can only travel through solid Existence of a shadow region in seismicwave pattern implies liquid outer core Existence of faint p-waves in shadow regionimplies solid inner corehttp://www.geo.mtu.edu/UPSeis/waves.html45II : Plate tectonics Heat flow from Earth’s interior drivesconvection in the Earth’s mantle… thisexerts forces on the Earth’s crust Plate tectonics… Earth’s crust is fragmented into 8 major“plates” and a number of minor “plates” Plates can… Slip past each other Come together (one slides under the other) Pull apart Volcanoes and Earthquakes tend to focusaround plate boundaries678Iceland ; Alfagja rift valleyBoundary of Eurasian and North American Plates9III : Structure of the Earth’satmosphere Composition (by number of molecules): 78% nitrogen 21% oxygen 1% water vapor 0.035% carbon dioxide Traces of other gases Atmosphere is very active Basic energy source for activity in Sun Complicated activity (weather) then driven viainteraction of solar heating, evaporation/condensationof water, rotation of Earth, interaction with surfacefeatures Longer term trends driven by life, geological events(volcanoes), subtle changes in solar output1011 Temperature of the Earth’s surface/atmosphere… Naïve treatment assuming black body radiation predictstemperature 246K (-27oC) Average temperature actually 287K (14oC) Why? The greenhouse effect Incoming solar radiation is in visible and near IR part ofspectrum… atmosphere transparent Heats surface and is re-radiated as mid-IR radiation…atmosphere much less transparent and can prevent energyfrom escaping Principal gases responsible (greenhouse gases) are carbondioxide (CO2) and methane (CH4) The vast majority of scientists agree that current globalwarming trend is due to man-made CO2Saw-tooth pattern due to seasonal variation in global vegetation1213Larsen B ice shelf (2002)14Another atmospheric problem on route to being solved… The Ozone HoleIV : The magnetosphere Sun produces a “wind” of charged particles(protons and electrons) Earth’s magnetic field deflects this wind…produces Shock wave in solar wind Magnetopause Van Allen Belts (tori of particles that have leakedthrough magnetopause) Aurorae (particles that manage to get through to theupper atmosphere) Magnetic activity is very important to thesurvival of life on