Chapter 3

Chapter 3 - Atlantic seafloor (Heezen and Plate Tectonics...

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Atlantic seafloor (Heezen and Tharp) Plate Tectonics How did the plates form? When – how old is the seafloor? What do the structures on the bottom tell us?
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Plate Tectonics Earth’s crust is a mosaic of slab-like plates that move with respect to each other
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Revolutions in Science 16 th Century Copernicus Planets revolve and the sun 17 th Century Newton Laws of gravity 18 th Century 19 th Century Darwin Evolution 20 th Century Einstein Relativity Plate tectonics
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The idea of moveable continents is not new Map by Antonio Snyder in 1858 (Pinet, 2000)
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As world maps developed semi-realistic outlines of the continents the symmetry of coastlines on opposite sides of the Atlantic was noted: Leonardo da Vinci Francis Bacon, 1620 Snyder map shown here, and others Edward Suess suggested a single large land mass explains similarity of fossils on either side of the Atlantic (ferns)
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Plate Tectonics Tectonic < tektōn, Gr., builder > of or having to do with building. The theory of plate tectonics represents a convergence of two ideas: 1. Continental drift (Wegener 1912) 2. Seafloor spreading (1960’s)
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Continental Drift •Proposed by Alfred Wegener, a German meteorologist, in 1912 •Suggested that continents were once all connected as a large landmass – Pangaea •Continents surrounded by a single ocean – Panthalassa •About 200 mya, Pangaea began to split apart to form modern continents •Originally rejected because Wegener had no viable mechanism to move continents (suggested it was a combination of gravitational force from equatorial bulge and tidal forces of the sun and moon)
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(1) Matching mountain chains on opposite sides of the Atlantic Wegener’s Evidence
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Wegener’s Evidence (2) Climates of the past present 300 mya •Glacial deposits found in rocks along the equator •Must once have been located closer to the poles, where glaciers have existed in the Earth’s past
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Wegener’s Evidence (3) Distribution of fossils •Identical fossils of extinct organisms incapable of swimming across an ocean found on both coasts of the Atlantic •Organisms must have occupied a united land-mass •E.g. Mesosaurus – aquatic reptile not strong enough to swim across the ocean
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Wegener perished in 1930 while on an expedition to Greenland, searching for
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This note was uploaded on 03/22/2009 for the course GEOL 103 taught by Professor Dr.ries during the Fall '08 term at UNC.

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Chapter 3 - Atlantic seafloor (Heezen and Plate Tectonics...

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