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summary ch1-7 - Geology 20A Geologic Hazards How Can the...

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Geology 20A- Geologic Hazards How Can the Earth Kill You? Page 1 of 6 Chapter 1- Energy Sources of Disaster Earth Energy Sources: 1) the Earth’s internal heat 2) the Sun 3) gravity 4) impact from extraterrestrial bodies Earth is ~4.57 billion years old. Direct evidence that the Earth is 4 to 4.2 billion years old with .35 to .57 billion years from Moon and meteorites. First 50 to 100 million years, gravitational pull compacted the interior with high-density liquid iron. 1) Primitive crust of low-density rocks at the surface of the Earth. 2) Large oceans 3) Heavier atmosphere. 97.3 Percent of Earth’s water covering 71 percent of Earth’s surface. Moon’s diameter of about 3,500 km. Earth has diameter of ~12,800 km. Return Period- larger and more energetic the event, the longer the return period—bigger is rarer. Twice as many deaths from solar-powered events as from disasters powered by Earth’s internal energy. Chapter 2- Plate Tectonics and Earthquakes Large oceans and small continents created 3.9B years ago. Photosynthetic bacteria was 3.5B years ago. Large continents present- 2.5B years ago Outer layers were 1.5B years ago. The Layered Earth Center of the Earth- dense, iron-rich core with 16 gm/cm cubed, measuring about 7,000 km in diameter Inner Core- 2,450 km diameter solid mass with temperatures up to 4,300 degrees Celsius Outer Core- mostly liquid, viscous movements generating Earth’s magnetic field Mantle- 2,900 km thick, rocky, compositions similar to chrondritic, stony meteorites. 83 percent of Earth’s volume and 67 percent of its mass; 5.7 to 3.3 gm/cm cubed. Uppermost-700 km thickness of mantle is depleted in light elements Lower- 2,200 km (1,365 mi) thick zone Continents- 2.7 gm/cm cubed Oceans- 1.03 gm/cm cubed Isostasy Lithosphere- pressure is dominant over temperature Asthenosphere- temperature is dominant over pressure, PLASTIC nature Isostasy- buoyancy principle to the low-density continents and mountain ranges that literally float on the denser mantle below. Plate Tectonic (takes about 250 million years)s 1) melted asthenosphere flows upward as magma 2) new lithosphere slowly moves laterally away from the zones of oceanic crust formation (searfloor spreading) 3) slabs ollide with another slab, older, colder, denser slab turns downward and is pulled by gravity back into the asthenosphere (subduction) 4) Begins the process of melting and reabsorbing into the mantle Movements of the iron-rich fluid in the outer core, which generate electric currents that in turn create the magnetic field. Fluid iron is an excellent conductor of electricity. Curie point- 550 degrees Celsius, atoms in iron-bearing minerals become magnetized in the direction of the Earth’s magnetic field at
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This note was uploaded on 03/22/2009 for the course GEOL 171 taught by Professor Tsoflias during the Spring '08 term at Kansas.

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summary ch1-7 - Geology 20A Geologic Hazards How Can the...

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