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Lecture 2

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University of Toronto St. George
Earth Sciences
Christine Burton

GLG205 J 2 May 13 Plate tectonics Hypothesis: - Earth is divided into mechanical layers o Outer layer is rigid lithosphere o Floats atop plastic asthenosphere - If we divide the earth by composition: crust J mantle J core - If we divide by -: lithosphere - asthenosphere Theory of plate tectonics - Z[Zo]Z}ZZ]Z]]]L}oZ~o]lZZZoo} l22ZK}o]} one another, and relative to the underlying asthenosphere - As plates move, their interiors remain relatively intact, while their boundaries undergo deformation o Mid-ocean ridges (MOR) J spreadingdiverging E.g. Mid-Atlantic ridge moving north American plate and Eurasian plate apart Atlantic growing wider o Subduction J sinking of the crust o Transform faults J sliding - If you live at the boundaries of the plate, there will be a lot of earthquake activity o E.g. Toronto vs. Vancouver that is at the edge of pacific plate Plate tectonics - Plate tectonic forces give rise to the formation of the crust, affect continental positions, and produce changes in global topography (e.g. valleys, mountains, water bodies) - The slow inexorable wearing down of the land surface of the earth would lead to its demise and reduction in height to sea level in less than 20 million years owing to weathering and erosion, if it were not for the return of the materials to the continents via plate tectonic forces Evidence for plate tectonics - Continents were connected o Matching coastlines E.g. south America matches the coastline of Africa o Similar rocks, glacial Z^ }ZZ_} LZ E.g. rocks on south America found to be same as rocks on African coastline o Same fossils E.g. fossils found in south America and Africa - Plate boundaries marked by: o Earthquakes @ZL[L}Ko]Z]8ZKZ}LJ edges of the plates o Volcanoes E.g. ring of fire around the pacific plate Many volcanoes on the edges of the plates o Mountain belts E.g. alps and Himalayas Located near the edges of plates New mountains are still growing because they are still being pushed Three types of plate boundaries
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