Planet Earth Our Home APOD 1
Earth a highly evolved planet = altered dramatically since formation, due to flow of energy from interior to surface 2
Planet Earth Facts diameter (equator) 12,756 km radius (equator) 6,378 km diameter (poles) 12,714 km mass 6 x 10 24 kg How do we know the mass of the Earth? 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 4
Planet Earth Facts average density = 5500 kg/m 3 5.5 times the density of water density: how well-packed matter is into some volume of space density = mass volume 5
Starting with what we know: rocks: density = 2000-4000 kg/m 3 iron: density -= 7800 kg/m 3 rocks near the surface density = 2400 kg/m 3 center must be ~ 12,000 kg/m 3 core must be very dense, i.e. iron compressed by weight of many layers 6
core mantle crust Model of the Interior 7
CORE: radius of 3500 km nickel & iron alloy solid inner core, molten outer core temperature > 6000 K 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) 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: silicates of aluminum, magnesium, iron - ocean basins and subcontinents silicates of aluminum, sodium, potassium - continents 10
granite lower density than basalt continents float on the basalt crust lower density than mantle crusts float on the mantle 11
differentiated: layers of least dense material on top, most dense on bottom How did the Earth get this way? APOD 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 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 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. 15
Magnetic Field Earth is like a giant bar magnet - field from south magnetic pole to north magnetic pole - axis of this magnet is 12 o off from the rotation axis 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 17
Planetary magnetic field should: fluid interior rapid rotation But this model does not always work out well! 18
Atmosphere oxygen for breathing shields us from cancer-causing UV radiation warmth for the surface distributes heat evenly around the Earth APOD 19
Atmosphere 78 % Nitrogen (N 2 ) 21 % Oxygen (O 2 ) 1 % Argon 0.03 % CO 2 traces 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 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 -18 o C Somewhere there s additional heat! 22
Greenhouse Effect Earth emits IR radiation - does not escape to space. 1/2 is absorbed by the atmospheric H 2 O and CO 2 atmosphere heats up, heat radiates back to ground 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. 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 O 3 (ozone) human activity => sharp drop in ozone 1950-1980 decreased by 1/2 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 O 3 molecules and there are about 1 million TONS of CFC s emitted per year. These remain for 100 years. 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 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 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 29
Atmospheric Circulation Local up and down convection cells Global north-south convection cells Rapid rotation of the planet 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 31
Earth: interior crust atmosphere oceans heat in the interior eventually flows to the surface heat on the surface eventually flows to space 10 13 J/sec is lost all of these are at different temperatures 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 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 34
Volcanism & Plate Tectonics volcanism: molten material comes up through the mantle and crust ocean floor is being renewed with new material continents: large plates floating on basalt mantle 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! 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 37
Evolution of Oceans volcanoes - bring up trapped gases CO 2, H 2 O - 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 38
Evolution of the Atmosphere model: first atmosphere hydrogen and helium low mass particles escaped into space 39
Evolution of Atmosphere second atmosphere: CO 2 (carbon dioxide) SO 2 ( sulfur dioxide) H (hydrogen) N (nitrogen) H 2 O (water) CH 4 (methane) NH 3 (ammonia) all outgassed from volcanoes 40
Evolution of Atmosphere large amounts of CO 2 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 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 42
Evolution of Surface Temperature temperature: depends on how much energy from Sun depends on how effectively the greenhouse effect is increase in CO 2, 5% in last 30 years could mean 2 o C rise by 2020 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) 44
Earth, Evolved Planet collide, stick together (accretion) mass gains energy, temperature increases later arriving debris makes impact craters Copyright by Calvin J. Hamilton 45
Mass Extinction Chicxulub impact crater NASA 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 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 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 49
Formation Process 600 million years ago formation and break up of continents Earth looked much as it does now 50
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 51