Jan23_09_Earth_structure_and_tectonics1

Jan23_09_Earth_structure_and_tectonics1 - Plate Tectonics...

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Plate Tectonics
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Formation of concentric layers (Heavier material sank toward the center of the earth and lighter material floated at surface, which is the reason for the earth’s concentric spherical layers) How do we know? Seismic tomography (similar to CT scan)
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Earth’s Interior Is Layered Inside Density is a key concept for understanding the structure of Earth. Density measures the mass per unit volume of a substance. Density = _Mass_ Volume Density is expressed as grams per cubic centimeter kilograms per cubic meter Water has a density of 1 g/cm 3 1000 kg/m 3
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The Study of Earthquakes Provides Evidence for Layering What evidence supports the idea that Earth has layers? The behavior of seismic waves generated by earthquakes give scientists some of the best evidence about the structure of Earth. Low frequency pulses of energy generated by the forces that cause earthquakes can spread rapidly through Earth in all directions and then return to the surface. (a) Earthquake waves passing through a homogenous planet would not be reflected or refracted (bent). The waves would follow linear paths (arrows). (b) In a planet that becomes gradually denser and more rigid with depth, the waves would bend along evenly curved paths. (c) P Waves (compressional waves) can penetrate the liquid outer core but are bent in transit. A P-wave shadow zone forms between 103 ° and 143 ° from an earthquake’s source. (d) Our earth has a liquid outer core through which the side- to-side S waves (shear waves) cannot penetrate, creating a large “shadow zone” between 103° and 180 ° from an earthquake’s source. Very sensitive seismographs can sometimes detect weak P-wave signals reflecting off the solid inner core.
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(solid) (solid and liquid) As going into the interior of the earth, temperature increases.
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