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NEW “PLANETOID” - SEDNA (Inuit Goddess of the Sea) Current Distance ~100 AU Perihelion Distance ~75 AU Mass ~1/2 Pluto Eccentricity 0.85 Semi Major Axis ~500 AU Period 11,000 years Aphelion Distance ~925 AU Inclination to Ecliptic 12 Degrees EARTH AS A PLANET Chapter 7 SOME PROPERTIES of EARTH Semi major Axis 1.00 AU Period 1.00 year Mass 5.98 x 1024 kg Diameter 12,756 km Escape Velocity 11.2 km/s Rotation Period 23h 56m 4s Surface Area 5.1 x 108 km2 Atmospheric Pressure 1.00 bar EARTH as a PLANET Only planet with water in liquid form. Composition: iron, silicates, oxygen. Density: highest in Solar System. Interior: 4 major layers – inner core, outer core, mantle, crust. EARTH as a PLANET Only planet with water in liquid form. Composition: iron, silicates, oxygen. Density: highest in Solar System. Interior: 4 major layers – inner core, outer core, mantle, crust. Magnetic Field and Magnetosphere: Earth behaves as if it had a bar magnet inside it. MAGNETOSPHERE and VAN ALLEN BELTS The MAGNETOSPHERE SHAPE EARTH’S STRUCTURE – HOW DO WE KNOW IT? SEISMIC WAVES Earthquakes produce two kinds of waves that travel through our planet. P (pressure) waves are longitudinal waves analogous to those produced by pushing a spring in and out. S (shear) waves are transverse waves analogous to waves produced by shaking a rope up and down. SEISMIC WAVES Earthquakes produce two kinds of waves that travel through our planet. P (pressure) waves are longitudinal waves analogous to those produced by pushing a spring in and out. S (shear) waves are transverse waves analogous to waves produced by shaking a rope up and down. P waves travel through solids and liquids (5-6 km/s). S waves cannot travel through liquids (3-4 km/s). Velocity of waves depends on density of material in which they travel. Velocity is faster in higher density materials. S and P WAVE PATHS FLASHCARD P WAVES MOVE AT ABOUT 5 KM/S. HOW LONG WILL IT TAKE A P-WAVE TO REACH THE OPPOSITE SIDE OF EARTH AFTER AN EARTHQUAKE? (RADIUS OF EARTH IS 6500 KM) A) ABOUT 4 SECONDS B) ABOUT 4 MINUTES C) ABOUT 40 MINUTES D) ABOUT 400 MINUTES EARTH’S STRUCTURE Under Oceans Crust 6 km thick. Basalts (volcanic rock, Si, O, Fe, Al, Mg). Under Continents Crust 20 to 70 km thick. Granite (volcanic silicates). EARTH’S STRUCTURE Mantle Down to 2900 km. Solid with some melting. Ejected volcanoes allows study. Core 3500 km radius. Outer core is liquid. Inner core dense and solid. Inner core rich in heavy elements - Fe, Ni, S. Crust Mantle Outer Core Inner Core EARTH’S STRUCTURE Structure indicates that Earth is differentiated which suggests Earth was once molten so heavier elements could sink to core. Crust Mantle Outer Core Inner Core PLATE TECTONICS Earth’s crust consists of about 12 plates. PLATE TECTONICS Energy escaping from the interior drives the plates (few cm/year). 50 million years from now PLATE TECTONICS Where plates interact, dramatic changes occur in Earth’s crust. Rift Zones: Plates pulling apart. Material rises from mantle to fill spaces (volcanoes). E.g. Mid Atlantic Ridge. PLATE TECTONICS Where plates interact, dramatic changes occur in Earth’s crust. Subduction Zone: Two plates come together, one forced down and melts. Earthquakes and volcanoes common along subduction zones. PLATE TECTONICS Coastal BC is on the upper part of a subduction zone. SAN ANDREAS FAULT ACTIVE SITES on EARTH’S SURFACE ACTIVE SITES on EARTH’S SURFACE CONTINENTAL DRIFT FLASHCARD AT 2 CM/YEAR, HOW LONG WOULD IT TAKE A TYPICAL PLATE TO TRAVERSE THE PRESENT WIDTH OF THE ATLANTIC OCEAN, ABOUT 6000 KM? A) 3 X 106 YR B) 1.2 X 107 YR C) 3 X 108 YR D) 1.2 X 109 YR > 100 km Ozone Layer Atmosphere very thin, constant leakage of H and He 50 - 80 km, O3, absorbs UV radiation 10 - 80 km, cold (-50ºC), Stratosphere cloudless < 10 km, most atmosphere Troposphere here. (N2 78%, O2 21%, Ar 1%, traces H2O, CO2) GREENHOUSE EFFECT CO2 content of atmosphere is critical for its role in retaining heat from Sun. Greenhouse Effect: Earth absorbs sunlight and re-emits it as infrared (IR) radiation (Earth acts like a blackbody). CO2 transparent to sunlight but absorbs IR acting like a blanket. The more CO2, the hotter Earth is. GREENHOUSE EFFECT and GLOBAL WARMING Greenhouse effect has raised Earth’s average temperature by 23ºC. Without the greenhouse effect, Earth’s average temperature would be below freezing and Earth would be in a constant global ice age. GREENHOUSE EFFECT and GLOBAL WARMING CO2 levels are increasing. Prediction: rising CO2 levels will lead to global warming with uncertain consequences. Vegetation map Rainforests extract CO2 Destruction rainforests This plus increasing fossil fuel burning causes increasing CO2 by 0.5%/yr Exacerbates Global Warming Cf Venus – 700K LIFE on EARTH Earth is the only planet known to be harbouring life. Life arose early on. Fossils date back 3.5 billion years. Origin of life is unsure. Miller experiment: produced amino acids and other pre-biological molecules from primitive Earth atmosphere - mainly methane, water, ammonia, CO2, no O2. LIFE on EARTH Development Use Free of plants: up CO2 and produce O2 - photosynthesis. O2 in atmosphere 2 billion years ago. Formation Protects of the ozone (O3) layer Earth from UV. This allowed life to leave protective oceans and colonize the land. Not possible earlier. COSMIC INFLUENCES on EARTH’S EVOLUTION Moon is heavily cratered Where are Earth’s craters? Most lost by erosion and geological activity. - caused by impacts. COSMIC INFLUENCES on EARTH’S EVOLUTION More than 150 impact craters are still recognized on Earth’s surface. METEOR CRATER 0.1 km meteor Crater size = 10 x size of impacting object 1.2 km COSMIC INFLUENCES on EARTH’S EVOLUTION More than 150 impact craters are still recognized on Earth’s surface. COSMIC INFLUENCES on EARTH’S EVOLUTION Concern is that a large object, ≥10 km, will collide with Earth releasing a few billion times as much energy as Hiroshima bomb. COSMIC INFLUENCES on EARTH’S EVOLUTION Concern is that a large object, 10 km, will collide with Earth releasing a few billion times as much energy as Hiroshima bomb. One such object crosses Earth’s orbit every 100 million years. ORBITS of the 100 LARGEST KNOWN NEAR-EARTH ASTEROIDS Mean Time to Impact Earth (Years) IMPACT FREQUENCY 1.00E-12 Impactors on the surface of the space shuttle 1m, 30sec 1.00E-09 Shooting stars 1 mm, 30 sec 1.00E-06 1.00E-03 Meteorites 1m, 1yr 1.00E+00 1.00E+03 Arizona Crater 100 m, 104 yr 1.00E+06 1.00E+09 1.00E-08 Sudbury, Ontario 10 km, 108 yr 1.00E-04 1.00E+00 Diameter (Metres) 1.00E+04 1.00E+08 COSMIC INFLUENCES on EARTH’S EVOLUTION More than 150 impact craters are still recognized on Earth’s surface. METEOR CRATER 0.1 km meteor Crater size = 10 x size of impacting object 1.2 km TUNGUSKA EVENT Siberia June 30, 1908 Projectile exploded before impacting Earth Projectile’s mass estimated to be 100,000 tons Caused widespread damage. TUNGUSKA EVENT THE SOLAR SYSTEM Comets can be captured by Jupiter. Actually orbit Jupiter – orbits unstable. Comet Shoemaker-Levy9 discovered 1992 Broke into fragments near “Peri-Jupiter” Fragments predicted to crash into Jupiter 1994 SHOEMAKER-LEVY9 COMET IMPACT Earth’s View Voyager’s View SHOEMAKER-LEVY IMPACT DEVELOPMENT of DUST CLOUD Impact IMPACT DUST CLOUDS IR IMAGE of IMPACTS Io COSMIC INFLUENCES on EARTH’S EVOLUTION con’t EFFECTS of a MASSIVE IMPACT EFFECTS of a MASSIVE IMPACT Global earthquakes. Huge tidal waves. Dust high up in the atmosphere. Block out Sun for about one year, kills photosynthesis. World-wide fires, forests and grasslands destroyed. Highly acidic rains. Animals depending on plants die (dinosaurs?), rise of mammals. EXTINCTIONS, the SOLAR SYSTEM and our GALAXY Past 100 million years many large scale extinctions (~ 10) identified on Earth. In these, a significant fraction of existing species were extinguished. Best known is extinction of the dinosaurs 65 million years ago after flourishing for 100 million years. EXTINCTIONS, the SOLAR SYSTEM and our GALAXY What caused the extinctions? Impact of ~ 20 km asteroid. Evidence: crater in Gulf of Mexico and Iridium layer. EXTINCTIONS, the SOLAR SYSTEM and our GALAXY What caused the extinctions? Impact of ~ 20 km asteroid. Evidence: crater in Gulf of Mexico and Iridium layer. Nearby supernova (depletes O3, forming NO2). Crab Nebula EXTINCTION of the DINOSAURS ALTERNATE DINOSAUR EXTINCTION THEORY SPIRAL GALAXY EXTINCTIONS, the SOLAR SYSTEM and our GALAXY Supernovae and impacts more likely when Sun passes through spiral arm in our Galaxy Oort cloud comets get perturbed. OORT CLOUD GETS PERTURBED