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WORLD GEOGRAPHY 3202 INTRODUCTION The Size of the World The Earth’s Interior • • • • Crust (Lithosphere) Mantle Outer Core Inner Core Inner Core • The deepest part of the earth (1512 miles deep) is a solid that contains both iron and nickel. • It is because of this that the center of the earth is a magnet, a compass. • It generates a magnetic field that protects the earth from flying out of orbit. Outer Core • Outside of the inner core lays the outer core (1419 miles deep). • This is much like the inner core with the exception that it is a liquid that contains sulphur and oxygen (which lowers the melting point). Mantle • Occupying 1789 miles of the earth is the magma (iron and magnesium) that makes up the mantle. • Upper and lower • It is extremely hot!! • goopy; very plastic-like. (upper mantle) • Mostly solid (lower mantle) Crust • Also called lithosphere • This is the top layer of the earth, which is basically hardened mantle (magma). • It contains two segments, the oceanic and continental crusts. • Note: this is the same crust, it just depends how thick it is to determine if it is part of the Oceanic or Continental Crust. Read About Earth’s interior • Our Text p. 4-6 Theory Of Continental Drift • Alfred Wegener • It is this German man to whom we credit with the proposal of the theory of Continental Drift. • While pondering the similarities between the coastlines of South America and Africa, Wegener came up with an idea: • What if the continents were once all connected and just drifted over the years? Wegener’s Proof Wegener’s Proof Wegener’s Proof The Flaw in Wegner’s Theory • He thought that each of the continents were a separate plate--they were just drifting on a neverchanging ocean. • Like styro-foam floating on a pool of water!! Missing Proof • Wegener could not explain what mechanism was powerful enough to move huge continents • Scientist’s never believed him Canadian Correction • J. Tuzo Wilson • the 1960’s Canadian scientist who resurrected Wegner’s theory after years of disbelief by the science community. • Today, we know that that's false, thanks to the discovery of crustal plates. • The plates of the earth are not composed of just land; they're composed of ocean too. Canadian Correction – cont’d • In some cases, the plates are just land, in others they're just ocean, and, in still other cases, they consist of land and ocean. • They each have different boundaries and move in all different directions. Plates of the earth p. 12 Continental Drift Animation Continental Drift • refers to the movement of the more than 20 plates (9 major) due to convergent, divergent, and transform boundaries. • The continents drift at a rate of 2 inches a year. • Started 200 million years ago • Pangea (land) & Panthalasa (sea) Plate Tectonics • Tectonic plates move or float on top of the upper mantle. • However they do not float freely. • The plates are forced in specific directions by the flow of magma beneath. Plate Tectonics – cont’d • Plates move with the flow of magma. • The magma closer to the core heats and then rises towards the surface as its density decreases. • Once the rising magma reaches the lithosphere it moves in opposite directions. • The magma forms convectional currents. Convection Currents Plate Tectonics – Convection Currents Divergent Boundaries • Tensional Forces occur where two tectonic plates are pushed apart. The tension is created as the plates move away from each other. • Ridge Zones sometimes occur where two plates move apart. The magma rises between the plates and forms a ridge. • Again caused by convectional currents in the magma Tensional Forces – Ridge Zones This diagram above shows “Sea Floor Spreading” Where’s the TENSION? Convergent Boundaries • Compressional Forces occur where two tectonic plates come together. They compress against each other. • Subduction Zones sometimes occur where compressional forces result from two plates colliding and one plate slips under the other. • Again caused by convectional currents in the magma Compressional Forces – Subduction Where’s the Subduction / Compression?