Plate Tectonics Theory.docx

Plate Tectonics Theory.docx - Plate Tectonics Theory Late...

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Plate Tectonics Theory - Late 60s - Combining hypotheses of continental drift and seafloor spreading - Idea: earth surface divided into few large thick plates moving and changing over time - Intense geologic activity at boundaries of plates - Explains volcanos, earthquakes, mountains - Alfred Wegner o First proposed in 1915 o Supercontinent Pangaea o Rocks and fossils, glaciation patterns acted as evidence - Hypothesis rejected originally, no driving force o Centrifugal force and moon’s tidal pull insufficient to plow continents through sea floor - Henry Hess in 62 o Seafloor moves away from mid-oceanic ridge due to mantle convection o Convection is circulation driven by rising hot material and/or sinking cooler material - Marine magnetic anomalies – bands of stronger and weaker than average mag. Field strength - Seafloor age – increases with distance from mid-oceanic ridge - Plate motion can be directly measured – using satellites, radar - Plates composed of rigid lithosphere, float upon ductile asthenosphere -
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