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University of Guelph
Environmental Sciences
ENVS 2250
Steve Sadura

Natural Disasters Unit 1 January 19, 2013 Layers of the Earth Structure of the Earth  The Core – an iron nickel mix and is though tot be solid at the center and liquid around the outside o 6960 km in diameter o 16.4% of earth’s volume but about 1/3 of its mass o Solid inner core, 2450 km in diameter, 13 g/cm3 in density  Spins separately from the rest of the planet  Rotates in the same direction but 1 degree per year faster  The differential movement of material may be part of what generates a magnetic field o Liquid outer core, 6972 km in diameter, 9.7 – 12.2 g/cm3  Heat is generates by the decay of radioactive isotopes such as potassium 40 (40K) which has a half life of 1.25 billion years – long enough to have generated heat throughout the earths history  The Mantle – mostly rocky and less dense (than the core) o 2900 km thick shell of silicate rock o 80% of the earth’s volume o 5.7 g/cm3 at the base to 3.3 g/cm3 near the crust in density o Seismic waves travel faster in more dense materials (both P and S waves travel through the mantle so we know it’s a solid) o Upper mantle, basaltic magma o Rock revealed is commonly peridotite – a black rock containing mostly olivine, pyroxene and plagioclase feldspar o Also exhibits slow convective movements  Solid when energy inputs are fast  Liquid when energy inputs are slow o Drives movements of earths surface  The Crust – the brittle surface layer of the planet o Thin and rocky o Oceanic crust – thinner and relatively young  Between 5 – 10 km thick  Nowhere is it older than 200 millions years  Constantly being produced at mid-ocean ridges and recycled at continental margins  Denser than continental crust – 3.0 g/cm3  Subduction – when oceanic crust slides underneath continental crust  Basaltic composition  Gabbro – a coarse-grained rock formed when this magma cools a great depths Natural Disasters Unit 1 January 19, 2013  Pillow Lavas – occurs where magma makes it to the surface – typical of underwater basaltic eruptions  MOHO Discontinuity – the boundary between the crust and the mantle o Continental crust – thicker and much older  2.7 g/cm3 in density  The continents are made up of predominately granite  On average 35-40 km thick but can be 70km or more under high range mountains  Older rock is found towards the center of the continents are get younger as you move outwards  The center of the continents are more geologically stable (few earthquakes or volcanic eruptions)  Great Rift Valley – The Magnetic Field  Deflects away harmful solar radiation  The sun is constantly producing this solar wind – a mixture of x-rays, radio emissions, ionized gases, hydrogen atoms, protons and electrons that blow outward at about 400-700km/second o Some of these charged particles become trapped in our magnetic field and create the auroras  Thought to have been produc
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