chapt03gh - Chapter 3 Earth Structure Geologic Structure of...

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1 1 Geologic Structure of Earth Geologic Structure of Earth - The interior of The interior of the Earth is layered. the Earth is layered. Concentric layers: crust, mantle, liquid outer core and solid inner core. Evidence (indirect) for this structure comes Evidence (indirect) for this structure comes from studies of Earth ’s dimensions, density, s dimensions, density, rotation, gravity, magnetic field, behavior of seismic waves and meteorites. Chapter 3 – Earth Structure 2 3 Density is a key concept for understanding the structure of Earth – differences in density lead to stratification (layers). Density measures the mass per unit volume of a substance. Density = _Mass_ Volume Density is expressed as grams per cubic centimeter. Water has a density of 1 g/cm 3 Granite Rock is about 2.7 times more dense 4 S waves – Secondary, Secondary, ‘side side -to to -side side ’ or shear waves, or shear waves, arrive second, arrive second, cannot pass through liquid , pass through , pass through solid, oscillate in the direction transverse to solid, oscillate in the direction transverse to propagation P waves – Primary, Primary, compressional compressional , arrive first, pass through solid, liquid and gas, oscillate in the direction through solid, liquid and gas, oscillate in the direction of propagation Waves associated with earthquakes: Seismograph Minutes P 01 0 3 04 0 5 0 Surface waves Mantle P S Focus Core 20 S 5 6 Evidence that supports the idea that Earth has layers comes from the way seismic waves behave as they encounter different material inside Earth and as the material is either liquid or solid
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2 7 Earth Earth ’s layers s layers – chemical composition and chemical composition and physical properties ¾ Core : ~ 3500 km thick, average density 13 g/cm 3 , 30% of Earth Earth ’s mass and 16% of its volume s mass and 16% of its volume • Inner core Inner core : radius of 1200 km, primarily Fe & Ni : radius of 1200 km, primarily Fe & Ni @Temp of 4000 -5500 5500 °C, solid, av. den. 16 g/cm3 C, solid, av. den. 16 g/cm3 • Outer core Outer core : 2260 km thick, Temp of 3200 : 2260 km thick, Temp of 3200 °C, C, liquid (partially melted), viscous, less dense ¾ Mantl Mantl e: 70% Earth e: 70% Earth ’s mass & 80% of its volume, 2866 km s mass & 80% of its volume, 2866 km thick, @ Temp of 100 -3200 3200 °C, Mg C, Mg -Fe silicates, solid but Fe silicates, solid but can flow , average density 4.5 g/cm 3 Note: inner core may be rotating faster than mantle – can be hotter than the Sun can be hotter than the Sun ’s surface (more than 6, 500 deg C! ) s surface (more than 6, 500 deg C! ) ¾ Earth Earth ’s outer layer is the Crust: cool, rigid, thin surface s outer layer is the Crust: cool, rigid, thin surface layer – rocks on crust side are chemically different than rocks on crust side are chemically different than rocks on mantle side – separation is called separation is called Mohorovi č i ć discontinuity 8 Earth s Crust: cold, brittle thin layer, 0.4% of Earth s mass and 1% of its volume ¾ Continental Crust: Primarily granitic type rock (Na, K, Al, SiO 2 ) 40 km thick on average Relatively light, 2.7 g/cm 3 ¾ Oceanic Crust
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chapt03gh - Chapter 3 Earth Structure Geologic Structure of...

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