ESS 7 Lecture notes - ESS 7 January 9th(Lecture 1 Forgot...

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ESS 7 January 9 th (Lecture 1) Forgot iClicker Course Themes: 1. Earth as a system 2. Plate tectonics 3. Geologic time 4. Earth-human interactions -Natural hazards -Environmental problems 5. Scientific method Geologic time scale 1. 1 Ga = 1 billion years ago 2. 1 Ma = 1 million years ago 3. 1 Ka = 1 thousand years ago The Big Bang - All mass and energy in a single point - Exploded ~13.7 Ga and continued its expansion After the Big Band -Rapid cascade of events: o Universe expanded, cooled and decreased in d o Elements bonded o Gravity caused collapse into gaseous nebulae o Condensed nebula formed flattened accretion discs. o Heat and mass from collapse cause nuclear fusion – stars born o Nuclear fusion in stars produced heavier elements (up to Fe) o Heavier elements are produced during supernova (exploding stars) Formation of our solar system - A 3 rd , 4 th , or nth generation nebula formed ~4.57 Ga. o Hydrogen and He left over from big bang o Heavier elements produced by stellar nucleosynthesis and supernova explosions January 11 th (2 nd lecture) Our solar system consists of: sun, planets, moons, and other objects Lies in the Milky Way Galaxy (120k light years) Earth shares solar system with 7 planets (4.57 Gal) The planets o Orbits a star o Spherical o Cleared its neighborhood of objects o Two types of planets: Terrestrial (Earth-like) – Small, dense, rocky Jovian (Jupiter-like) – Large, low density, gas-giant planet Formation of the moon o After formation of earth, Mars sized planetoid collides with Earth
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o Debris forms a ring around the Earth o The debris coalesces and forms the moon o “Giant impact hypothesis” Formation of Earth’s layered structure o Early earth was a molten ball of magma due to gravitational heating and radioactive decay Dense metals (Fe, Ni) sank to core Less dense magma rose and cooled to produce a primitive rocky crust In between, mantle is composed of intermediate density material Earth’s interior layers (Chemical Differences) o Crust Chemical Composition: (Only Silly Asses In College Study Past Midnight / O, Si, Al, Fe, Ca, Na, K, Mg ) Two types of crust: 1. Continental: Granitic, high silica 2. Oceanic: Basaltic, higher Fe and Mg o Mantle Solid rock layer between crust and core More Fe rich and denser than Crust ~3000km thick. 82% of Earth’s volume Below ~100-150 km), rock is hot enough to flow o Core Inner core: solid Outer core: liquid Why’s Earth’s interior hot? o KE and Gravitational energy -> thermal energy Primordial heat from planet formation Early bombardment by asteroids and comets o Radioactivity Decay of radioactive isotopes produces heat Geothermal gradient o Rate of change of temp with depth o In crust, avg gradient is 25C/Km o TauTona Gold Mine, South Africa o World’s deepest mine, 3.9Km deep o How hot is the mine, assuming avg: temperature decrease? ~100C Earth’s layers can also be sub-divided based on their physical properties o Lithosphere: outermost 100-150 km of earth
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