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Transcript
Plate Tectonics What is the Theory of Continental Drift? What is the Theory of Continental Drift? • Alfred Wegner, 1915 • The continents were once a super-continent called Pangea • the continents are plowing through the ocean floors---most people didn’t believe this What evidence supports this theory? • • • • Africa & South America look like they fit together similar fossils, rocks, and glacial striations Rock magnetism Age of bedrock Matching Mountain Ranges What is the Theory of Plate Tectonics? • Earth's crust is made up of plates that ride on top of the asthenosphere (partially melted layer) • The plates move due to convection currents in the mantle What evidence supports this theory? • distribution of earthquakes and volcanoes • sea-floor spreading How do oceanic and continental crust compare with regard to thickness and density? continental Density (ESRTs pg 10) thickness oceanic What are the primary rocks which make up the continental and oceanic crusts? continental crust oceanic crust Low-density, lightcolored, coarsegrained, felsic, igneous rock High density, darkcolored, fine-grained, mafic igneous rock Plate Boundaries • Plate Boundary Animations Subduction Boundaries • How the Earth Was Made • 15min 50s-17min 35sec What are these types of plate boundaries? • Ocean-continental or ocean-ocean convergent boundaries (SUBDUCTION) • Trenches, volcanoes, deep earthquake • Peru Chile Trench • Continental – continental convergent (COLLISION) boundary • Mountain building • Himalayas • • • • Transform fault Sliding past each other Shallow earthquakes Ex: San Andreas Fault – Fault: break in Earth’s crust where movement has occurred • Divergent plate boundaries • New crust made • Alternating magnetic orientation • Ex: Mid-Atlantic Ridge What happens to the age of oceanic crust as distance increases from a ridge?