Chapter 6Why is the Earth round?Shape and Size of the EarthComposition of the EarthDensity of the EarthWhat shape is the Earth?The Earth’s InteriorUsing Earthquakes to See Inside the EarthUsing Earthquakes to See Inside the EarthThe Earth’s InteriorHow did the Earth get layers?Slide 12What is needed for differentiation to occur in a mixture?The Earth’s CoreSpeaking of Radioactive Decay…What we’ve learning from radiometric datingSlide 17Motions of the Earth’s InteriorTwo Main Types of Crustal MotionPlate TectonicsPlate TectonicsThe Discovery of Plate TectonicsPlate TectonicsWhat is the driving force behind plate tectonics?The Earth’s Magnetic FieldThe Earth’s Magnetic PolesThe Earth’s Magnetic PolesThe MagnetosphereThe AurorasWhich of the following are true of the Earth’s magnetic field?The AtmosphereThe AtmosphereComposition of the AtmosphereThe Greenhouse EffectThe Greenhouse EffectThe “Hole” in the Ozone LayerThe Ozone LayerSo where did the atmosphere come from?Which of the following is true about global warming?The Coriolis EffectCoriolis EffectPrecessionSlide 43Chapter 6The EarthWhy is the Earth round?•The Earth is round and (mostly) smooth because of gravity.•The more mass (i.e. the more gravity) a celestial body has, the more it can pull itself into a smooth round shape.Shape and Size of the Earth•Ancient astronomers knew the Earth was round, but assumed it was a perfect sphere with radius 6400 km (about 4000 miles).•The Earth is an “oblate spheroid,” not a perfect sphere.•The rotation of the Earth causes the equator to bulge.•This can be understood using Newton’s 1st Law.Composition of the Earth•The Earth is (to first order) a ball of rock flying through space at 30 kilometers per second.•The rock on the surface (the crust) is made up of many different kinds of minerals.•Oxygen and silicon usually appear together as silicates.•Sand (a silicate) is almost entirely pure SiO2.Density of the Earth•Density = mass / volume = how much “stuff” is packed into a given amount of space•Mass of the Earth = 6.0*1027 grams•Volume of the Earth = (4/3)πR3 = (4/3)*π*(6.4*108 cm3)3•Density of the Earth = 5.5 grams / cubic centimeter•Water = 1.0 g/cc •This is the average density over the whole planet. The rocks on the surface have densities lower than the average, so the interior must have densities higher than the average.What shape is the Earth?A. CircleB. EllipseC. SphereD. OvalE. Oblate spheroidF. Minty altoidThe Earth’s Interior•Deepest hole drilled is 12 km, less than 0.2% of the way to the center.•One way to “see” inside the Earth is to use the waves from earthquakes.•This is not too different from how doctors “see” the inside of your body with a sonogram.Using Earthquakes to See Inside the Earth•Two main types of seismic waves: S waves (transverse) P waves (longitudinal)•P (longitudinal) waves travel easily through both solids and liquids•S (transverse) waves only travel through solids, not liquids.Using Earthquakes to See Inside the Earth?The Earth’s Interior•Crust: Solid rock (mostly silicates), low-density, 20-70 km thick•Mantle: Hot “solid” rock (mostly silicates), extends roughly halfway to the Earth’s center•Liquid (outer) core: Most likely a mixture of iron, nickel, and maybe sulfur•Solid (inner) core: Most likely iron and nickel, 1/3 the radius of the inner coreHow did the Earth get layers?•Differentiation occurs a mixture of high-density and low-density materials melts•High-density material sinks, low-density material risesIf P waves travel through a substance, but not S waves, what do we know about the substance?A. The substance is liquidB. The substance is solidC. The substance is both liquid and solidD. The substance is worth a lot of moneyWhat is needed for differentiation to occur in a mixture?A. A range of densities in the mixtureB. The mixture to become liquidC. Both A and BD. Neither A nor BThe Earth’s Core•The Earth’s core is 6500 K, hotter than the surface of the Sun.•The temperature increases more rapidly near the surface and the temperature is more stable near the core.•Where does this heat come from?1) The Earth was born hot (the original source)2) Radioactive decay in the core (slowing the loss)Speaking of Radioactive Decay…•During radioactive decay, radioactive atoms decay into “daughter atoms,” and this happens in a predictable way.•Every half-life, half of the original radioactive material decays. (100 —> 50 —> 25, and so on)•This predictable rate means we can look at the ratio of radioactive atoms to daughter atoms in rocks to figure out how old those rocks are.What we’ve learning from radiometric dating•The oldest rocks on Earth are over 4 billion years old.•Yes, billion with a B. (4,000,000,000 = 4*109)•Rock samples from the moon and pieces of asteroids (meteorites) are as old as 4.55 billion years.•Individual crystals within old rocks on Earth date to about 4.4 billion years old.•All this points to an age of the solar system (and the Earth) of around 4.5 billion years.If there are 240 radioactive molecules of half-life 15 minutes, how many are left after 1 hour?A. 180B. 240C. 120D. 60E. 30F. 15G. 7 or 8H. ZeroMotions of the Earth’s Interior•Convection is the circulating movement of a heated gas or liquid.•The core supplies the heat, and the mantle (slowly) circulates.•The motion of the mantle against the crust causes the crust to move.Two Main Types of Crustal Motion•Rifting: Rising material in the mantle pulls sections of crust apart. •Subduction: Sinking material in the mantle causes two sections of crust to collide, and one is pulled under the other.Plate TectonicsPlate TectonicsThe Discovery of Plate Tectonics•1596: Abraham Ortelius notes that the coastlines of South America and Africa seem to fit together•1858: Antonio Snider-Pellegrini notes very similar fossils at matching sites across the ocean, conjectures the continents broke apart. •1912: Alfred Wegener publishes “The Origin of the Continents,” amassing evidence from fossil and geological records to support his claim.Plate TectonicsPangeaSupercontinentfrom 250 millionyears agoWhat is the driving force behind plate tectonics?A. Gravity between the crust and the coreB. Convection in the mantleC. Convection in the coreD. America’s strong desire to be further from EuropeE. MagnetsThe Earth’s Magnetic