The Living EarthIntroduction To Modern Astronomy IGuiding QuestionsAn Active EarthAn Active EarthThe Greenhouse EffectThe Greenhouse EffectEarth’s interior structure Earth’s interior structure Earth’s interior structure Earth’s interior structure Earth’s MagnetosphereEarth’s MagnetosphereEarth’s MagnetosphereEarth’s Atmosphere: CompositionEarth’s Atmosphere: CompositionEarth’s Atmosphere: TemperatureEarth’s Atmosphere: Temperature Earth’s BiosphereThe Distribution of Plant Life Earth’s Biosphere Final Notes on Chap. 9The Living EarthChapter NineIntroducing Astronomy (chap. 1-6)Introduction To Modern Astronomy IPlanets and Moons (chap. 7-17)ASTR 111 – 003 Fall 2006Lecture 09 Oct. 30, 2006Ch7: Comparative Planetology ICh8: Comparative Planetology IICh9: The Living EarthCh10: Our Barren MoonCh11: Sun-Scorched MercuryCh12: Cloud-covered VenusCh13: Red Planet MarsCh14: Jupiter and SaturnCh15: Satellites of Jup. & SaturnCh16: Outer WorldCh17: Vagabonds of Solar SystemGuiding Questions1. What is the greenhouse effect? How does it affect the average temperature of the Earth?2. Is the Earth completely solid inside? How can scientists tell?3. How is it possible for entire continents to move across the face of the Earth?4. How does our planet’s magnetic field protect life on Earth?5. Why is Earth the only planet with an oxygen-rich atmosphere?6. Why are prevailing winds generally from the west over most of North America but generally from the east in Hawaii?7. What are global warming and the “ozone hole”? Why should they concern us?Earth DataAn Active Earth•Active Atmosphere•Active Ocean •Active LandAn Active Earth• All activity in the Earth is powered by three sources of energy1. Solar energy2. Tidal forces (from Sun and Moon’s gravity)3. Earth’s internal heat (left over from the creation)•Atmosphere is powered by solar energy•Ocean is powered by solar energy and tidal forces•Land is powered by the internal heatThe Greenhouse Effect• Greenhouse effect: greenhouse gases in the atmosphere trap the infrared radiation emitted from the Earth’s surface, and raise the temperature of the atmosphereThe Greenhouse Effect• The Earth’s surface is directly heated by the radiation from the Sun, because the atmosphere is almost transparent to the visible light• The Earth’s surface emits infrared radation•The CO2gas and H2O water vapor, so called greenhouse gases in the atmosphere, strongly absorb the infrared radiation, thus trap the solar energy• The greenhouse effect raises the Earth’s surface temperature by 41°C– The average actual surface temperature is 14°C– If no greenhouse effect, the calculated surface temperature would be about -27°CEarth’s interior structure• Earth has a layered internal structure, due to chemical differentiation process in the early time– When Earth was newly formed, it was molten throughout its volume due to the heat from impact– Dense materials such as iron sank toward the center– Low-density materials rose toward the surfaceEarth’s interior structure• Present-day Earth has three layers: crust, mantle and core• Crust: 5 km to 35 km deep, solid, made of relatively light silicon-rich minerals• Mantle: 2900 km deep, solid, made of relatively heavy iron-rich minerals• Core: 2900 km – 6400 km deep, made of pure iron– Outer core: 2900 km – 5100 km deep, liquid– Inner core: 5100 km – 6400 km deep, solidEarth’s interior structure• Earth’s internal structure is deduced by studying how the seismic waves produced by Earthquakes travel through the Earth’s interior• Seismic waves refract or change the path as they pass through different part of the Earth’s interiorEarth’s interior structure•From surface to center, temperature (as well as pressure) rises steadily from 14°C to 5000°C •The state depends on the actual temperature relative to the melting temperature– Melting temperature is determined by chemical composition and pressure– The mantle is primarily solid because the temperature there is lower than the melting point– The outer core is liquid, because the temperature there is higher than the melting pointPlate Tectonics•The world map indicates that the continents would fit rather snugly against each other. •Alfred Wegener, in 1915, suggested the idea of “continental drift”. •All continents have originally been a single gigantic supercontinent, called Pangaea (meaning “all lands”)Plate Tectonics• About 200 million year ago, almost all continents were merged into a single supercontinent, called PangaeaPlate Tectonics• Pangaea first split into two smaller continents, Laurasia in the north, and Gondwana in the southPlate Tectonics• The continental drifting speed is several cm per year– For example, at a rate of 3 cm/year over 200 million years, the drifting distance is 6000 km• Plate tectonics is caused by the internal heat of the Earth• Asthenosphere is the upper levels of the mantle that are hot and soft enough to permit a plastic flow.• Internal heat causes convection flows in asthenosphere• Molten material from asthenosphere wells up at oceanic rifts, producing seafloor spreading, and is returned to the asthenosphere in subduction zones• As one end of a plate is subducted back into the asthenosphere, it helps to pull the rest of the plate along Plate Tectonics• The Earth’s crust and a small part of its upper mantle form a rigid layer called the lithosphere.• The lithosphere is divided into plates that move over the plastic layer called the asthenosphere in the upper mantle• Most earthquakes occur where plates separate, collide, or rub together; plate boundaries are identified by plotting earthquake epicentersPlate TectonicsPlate Tectonics•The Mid-Atlantic Ridge– Lava seeps up from the Earth’s interior along a rift extends from Iceland to Antarctica– The upwelling motion of lave forces the existing crusts apart, causing seafloor spreading– As a result, South America and Africa are moving apart at a speed of 3 cm per yearPlate Tectonics•The Himalayas Mountain– The plates that carry India and China are colliding– Both plates are pushed upward, forming the highest mountains on the Earth• The motion of the liquid iron core of the Earth, which carries electric currents, generates magnetic fields• This magnetic field produces a magnetosphere that surrounds the Earth•