Question. Question. Question. Question. What are the topics of our last class? is the tendency of some minerals to break along flat surfaces?

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1 Question What are the topics of our last class? Question is the tendency of some minerals to break along flat surfaces? A. Crystal habit; B. Cleavage; C. Fracture; D. Hardness Question Calcite is a mineral. Question rock forms when magma rises to the Earth s surface, cools, and solidifies. A. silicate; B. carbonate; C. either; D. neither A. Metamorphic B. igneous; C. sedimentary; D. None of the above 1

2 Question GEOS 107 Planet Earth Limestone is rock. 4.3 Plate Tectonics A. Metamorphic B. igneous; C. sedimentary; D. None of the above Dr. Yang Deng Dept. of Earth and Environmental Studies Montclair State University Alfred Wegener The Continental Drift Hypothesis Alfred Wegener, a young German scientist The fit of S. America & W. Africa East African rift The African and South American coastlines appear to fit together like adjacent pieces of a jigsaw puzzle on Wegener s reconstruction map. The red areas show locations of distinctive rock types in South America and Africa. The brown regions are the continental shelves, which are the actual edges of the continents. 2

3 Alfred Wegener The Continental Drift Hypothesis Assembled all continents together: Pangea Laurasia (north: North America and Eurosia) Gondwanaland (south: South America, Africa, Antarctia, India and Australia) Geographic distributions of plant and animal fossils on Wegener s map indicate that a single supercontinent, called Pangea, existed from about 300 to 200 million years ago. Alfred Wegener The Continental Drift Hypothesis Continental drift The idea that a single supercontinent broke apart and pieces drifted away No plausible mechanism One thought: the land masses plowed thru ocean crust like a ship on ice Or that continental crust simply slid over ocean crust Neither well received Replaced by the more complete plate tectonics theory Earth is a layered planet. The insert is drawn on an expanded scale to show near-surface layering. note that the average thickness of the lithosphere varies from about 75 kilometers beneath the oceans to about 125 kilometers beneath continents. 3

4 Earth s Layers Crust thinnest layer Oceanic Continental Mantle Uniform composition Varying rock strength w/ depth The Earth s Layers Lithosphere crust + rigid upper mantle Asthenosphere hot, plastic-like mantle Base of mantle strong again Core outer liquid, inner solid, both Ni-Fe Earth s internal temperature increases with depth. At the center of Earth, the temperature is close to 7,000 C, hotter than the Sun s surface. For reference, the temperature of an oven baking a chocolate cake is about 175 C, and a heated steel bar turns cherry red at 746 C 4

5 Sea-Floor Spreading Hypothesis Mid-Oceanic Ridge system Found after WWII The longest mountaindsf chain Earth s internal pressure increases almost linearly with depth Sea Floor: Mid-Oceanic Ridge System Mid-Ocean Ridge system continuous mountain chain connected across the globe, about ~80,000km long Sea Floor: Mid-Oceanic Ridge System Rift valley 1-2km wide split along the ridge s center where new crust forms Normal faults and earthquakes in valley From USGS 5

6 Sea Floor: Mid-Oceanic Ridge System Mid-Atlantic Ridge Transform faults hundreds of fractures crossing perpendicular to the ridge A chart of the sea floor. The Mid-Oceanic ridge system is a submarine mountain chain that encircles the globe like the seam on a baseball. The Mid-Atlantic ridge, shown in red, runs through iceland. Magnetic orientation of sea-floor rocks near the ridge are shown in the lower-left portion of the map. The green stripes represent sea-floor rocks with normal magnetic polarity, and the blue stripes represent rocks with reversed polarity. The stripes form a symmetrical pattern of alternating normal and reversed polarity on each side of the ridge. As new oceanic crust cools at the Mid-Oceanic ridge, it acquires the magnetic orientation of Earth s field. Alternating stripes of normal (green) and reversed (blue) polarity record reversals in Earth s magnetic field that occurred as the crust spread outward from the ridge. (every 500,000 years) 6

7 Plate Tectonics 7