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Planet Earth APOD Our Home Intro to Solar System Earth, Our Home 1 Earth a highly evolved planet = altered dramatically since formation, due to flow of energy from interior to surface Intro to Solar System Earth, Our Home 2 Planet Earth Facts diameter (equator) radius (equator) diameter (poles) mass 12,756 km 6,378 km 12,714 km 6 x 1024 kg How do we know the mass of the Earth? Intro to Solar System Earth, Our Home 3 Measuring the Mass • Kepler’s Third Law (as revised by Newton • something orbiting the Earth (moon or satellite (must be small mass) • period of the orbiting body • average distance of the orbiting body Intro to Solar System Earth, Our Home 4 Planet Earth Facts average density = 5500 kg/m3 5.5 times the density of water density: how well-packed matter is into some volume of space density = mass volume Intro to Solar System Earth, Our Home 5 Starting with what we know: rocks: iron: density = 2000 - 4000 kg/m3 density -= 7800 kg/m3 rocks near the surface density = 2400 kg/m3 center must be ~ 12,000 kg/m3 core must be very dense, i.e. iron compressed by weight of many layers Intro to Solar System Earth, Our Home 6 Model of the Interior • core • mantle • crust Intro to Solar System Earth, Our Home 7 CORE: radius of 3500 km nickel & iron alloy solid inner core, molten outer core temperature > 6000 K Intro to Solar System Earth, Our Home 8 MANTLE: 2400 km thick rock - iron, magnesium, silicon, oxygen (olivine) - silicates (compounds of silicon and oxygen) temperature 3800 K (base) 1300 K (top) steady pressure causes mantle to flow (like a plastic) Intro to Solar System Earth, Our Home 9 CRUST: 8 km thick under the oceans 70 km thick under the continents solid surface layer - rocks solidified from molten lava = igneous rocks basalt: granite: Intro to Solar System silicates of aluminum, magnesium, iron - ocean basins and subcontinents silicates of aluminum, sodium, potassium - continents Earth, Our Home 10 granite lower density than basalt continents float on the basalt crust lower density than mantle crusts float on the mantle Intro to Solar System Earth, Our Home 11 differentiated: layers of least dense material on top, most dense on bottom How did the Earth get this way? APOD Intro to Solar System Earth, Our Home 12 Model for Early Earth well-mixed at time of formation then heated, dense material sank to the core Heat: • stored energy from formation • radioactive decay - energy is transferred to the rocks and heats them Intro to Solar System Earth, Our Home 13 Age: 4.6 billion years old billion = 1000 million • radioactive dating - decay of radioactive isotopes oldest rocks 4 billion years old Greenland, Canada allow 1/2 billion yeas for crust to melt, then cool Intro to Solar System Earth, Our Home 14 • coincides with age of meteorites - 4.55 billion years old • coincides with age of lunar rocks - 4.6 billion years old Solar System formed along with the Sun 4.6 billion years ago. Intro to Solar System Earth, Our Home 15 Magnetic Field Earth is like a giant bar magnet - field from south magnetic pole to north magnetic pole - axis of this magnet is 12o off from the rotation axis Intro to Solar System Earth, Our Home magnetic axis 16 Magnetic Field Variations: changes intensity and direction (polarity reversal) - 9 times in 3.5 million years Dynamo model: • metallic core, partly liquid = good electrical conductor • acts like a large electromagnet and a giant generator • Earth’s rotation keeps this in motion Intro to Solar System Earth, Our Home 17 Planetary magnetic field should: fluid interior rapid rotation But this model does not always work out well! Intro to Solar System Earth, Our Home 18 Atmosphere • oxygen for breathing • shields us from cancer-causing UV radiation • warmth for the surface • distributes heat evenly around the Earth APOD Intro to Solar System Earth, Our Home 19 Atmosphere 78 % Nitrogen (N2) 21 % Oxygen (O2) 1 % Argon 0.03 % CO2 traces Intro to Solar System Earth, Our Home 20 Atmosphere & Light • some of the light is absorbed - blocked out by the atmosphere atmospheric extinction •sunlight is scattered by air molecules - blue light scatters easily => sky is blue - along the line of sight looks redder => sunset looks red atmospheric reddening Intro to Solar System Earth, Our Home 21 Greenhouse Effect 1/2 of the unreflected sunlight is absorbed by the ground - ground heats up - air near the ground becomes warmer This, in itself, would not give us the temperature we currently enjoy; it would be -18o C Somewhere there’s additional heat! Intro to Solar System Earth, Our Home 22 Greenhouse Effect Earth emits IR radiation - does not escape to space. 1/2 is absorbed by the atmospheric H2O and CO2 atmosphere heats up, heat radiates back to ground Intro to Solar System Earth, Our Home 23 Greenhouse Effect Earth’s surface is warmed by: direct sunlight IR radiation from the atmosphere Water and carbon dioxide are the chief greenhouse gases. Intro to Solar System Earth, Our Home 24 Ozone Layer UV is blocked by the atmosphere at about 30 km above the surface UV is absorbed => 3 Oxygen atoms to bind into O3 (ozone) human activity => sharp drop in ozone 1950 - 1980 decreased by 1/2 Intro to Solar System Earth, Our Home 25 Ozone Layer CFC’s contribute to the depletion of the ozone layer aerosol propellants solvents refrigerants volcanic eruptions One chlorine atom destroys 100,000 O3 molecules and there are about 1 million TONS of CFC’s emitted per year. These remain for 100 years. Intro to Solar System Earth, Our Home 26 Atmospheric Circulation convection: warm air rises, cool air sinks • sunlight heats ground and air • heated air expands, becomes less dense • expanded air rises • denser, cooler air sinks to fill in behind Local convection cells Intro to Solar System Earth, Our Home cumulus clouds 27 Atmospheric Circulation Global convection cells • warm air over equator is less dense than cooler air over the poles • warm air rises to the poles • cool air from poles sinks down to fill in Intro to Solar System Earth, Our Home 28 Atmospheric Circulation And, if that wasn’t enough! Earth rotates under all of this - forms spiral air flows cyclones ! APOD Faster rotating planet, stronger cyclonic effects Intro to Solar System Earth, Our Home 29 Atmospheric Circulation Local up and down convection cells Global north-south convection cells Rapid rotation of the planet Intro to Solar System Earth, Our Home 30 The Crust surface of the Earth is not smooth and flat why? why isn’t it eroded flat? somehow it’s being replenished heat flow: from Earth’s center drives the evolution of our planet heat: thermal energy transferred from one place to another Intro to Solar System Earth, Our Home 31 Earth: interior crust atmosphere oceans all of these are at different temperatures heat in the interior eventually flows to the surface heat on the surface eventually flows to space 1013 J/sec is lost Intro to Solar System Earth, Our Home 32 Continental Drift present continents were at one time one large land mass evidence: • reversals of Earth’s polarity are preserved in rock • same patterns on both sides of Mid-Atlantic Ridge • record of past changes recorded in the seafloor Intro to Solar System Earth, Our Home 33 rift: separation of crustal masses new material oozes out of the rift • seafloor expands 3 cm/year - this would be enough to push apart over a few million years Intro to Solar System Earth, Our Home 34 Volcanism & Plate Tectonics volcanism: molten material comes up through the mantle and crust ocean floor is being renewed with new material continents: Intro to Solar System large plates floating on basalt mantle Earth, Our Home 35 Volcanism & Plate Tectonics mountains: sea floor trenches: built from the collision of two plates plates get folded over and driven back through the mantle surface of the Earth is constantly recycled! Intro to Solar System Earth, Our Home 36 Volcanism & Plate Tectonics earthquakes and volcanoes predominate where plates are being created or destroyed ocean basins are the youngest surfaces center of continents are the oldest rifts: stretching, thinning, splitting of Earth’s crust HEAT FLOW drives plate tectonics Intro to Solar System Earth, Our Home 37 Evolution of Oceans volcanoes - bring up trapped gases CO2, H2O - outgassing • initially, no oceans - too hot • Earth cooled, water vapor outgassed • condensed as it cooled evidence: measure current rate of outgassing - can account for all of the oceans Intro to Solar System Earth, Our Home 38 Evolution of the Atmosphere model: first atmosphere hydrogen and helium low mass particles escaped into space Intro to Solar System Earth, Our Home 39 Evolution of Atmosphere second atmosphere: CO2 (carbon dioxide) SO2 ( sulfur dioxide) H (hydrogen) all N (nitrogen) outgassed H2O (water) from CH4 (methane) volcanoes NH3 (ammonia) Intro to Solar System Earth, Our Home 40 Evolution of Atmosphere • large amounts of CO2 ended up in oceans and rocks • 3 billion years ago: mostly methane and hydrogen very little free oxygen, no ozone • UV radiation interacted with methane, ammonia and water • atoms separated Intro to Solar System Earth, Our Home 41 Evolution of Atmosphere • hydrogen escaped • oxygen formed the ozone layer • nitrogen from the ammonia formed our atmosphere biological (plant life!) activity produced the high abundance of oxygen and now maintains it 600 million years ago - attained present level Intro to Solar System Earth, Our Home 42 Evolution of Surface Temperature temperature: depends on how much energy from Sun depends on how effectively the greenhouse effect is increase in CO2, 5% in last 30 years could mean 2o C rise by 2020 Intro to Solar System Earth, Our Home 43 Earth, Evolved Planet • most evolved planet • active world, powered by internal heat planetary formation: • collection of debris in space • gravity draws together • gravitational potential energy kinetic energy (heat) Intro to Solar System Earth, Our Home 44 Earth, Evolved Planet • collide, stick together (accretion) • mass gains energy, temperature increases • later arriving debris makes impact craters Copyright by Calvin J. Hamilton Intro to Solar System Earth, Our Home 45 Mass Extinction NASA Chicxulub impact crater Intro to Solar System Earth, Our Home 46 Formation Process 4.6 billion years ago accretion from smaller bodies bombardment by large objects planet of uniform materials atmosphere - H and inert gases Intro to Solar System Earth, Our Home 47 Formation Process 4.5 billion years ago radioactive heating melted interior Earth differentiated original atmosphere was lost second atmosphere outgassed by volcanoes surface cooled, rain began to fall Intro to Solar System Earth, Our Home 48 Formation Process 3.7 billion years ago continents appeared plate tectonics began mountains grew atmosphere evolved 2.2 billion years ago crust cooled plate activity began Intro to Solar System Earth, Our Home 49 Formation Process 600 million years ago formation and break up of continents Earth looked much as it does now Intro to Solar System Earth, Our Home 50 Earth, Our Home changed greatly since formation evolution driven by internal heat stored and from radioactive decay heat differentiated the interior heat drove tectonics and volcanism crust shaped by impacts wind and water has eroded the crust Intro to Solar System Earth, Our Home 51