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Transcript
The theory of plate Tectonics The Restless Earth Plate Tectonics Topic objectives • Understand continental drift and how the theory was discovered. • Be able to site evidence for continental drift from the works of Alfred Wegner. • Identify the super-continent Pangaea and the large sea Panthalassa. • Understand the importance and Mid-Atlantic Ocean ridge, its location and how the global seafloor is renewed. • Compare and contrast convergent & divergent boundaries. What is plate Tectonics? A crash course. • Tectonics- Greek (tektonikos)– construction. • For eons, man has wondered about the inner workings of the planet in which he inhabits. Serve it up on a plate. Tectonic plates • Blocks of Lithosphere (crust) that consists of the crust and the outermost layer of the mantle. • Not all plates are the same size. • All plates fit together like a puzzle. The players of the game. Types of crust found on Earth. • Oceanic Crust-found on the seafloor . • Continental Crust-less dense crust than Oceanic crust. Forms the continents. • Both ride on the Asthenosphere. Bound by one another… 3 Types of plate boundaries • Divergent- 2 plates move away from one another. • Magma rises to the surface and creates new crust. • Found on the ocean floor • Mid-Atlantic Ocean Ridge. Bound by one another… 3 Types of plate boundaries • 3 types of collisions can occur. • Convergent- when one plate collides into another. Going under… Subduction Plates • Subducting plates Oceanic dense crust is sunducted or pushed under the lighter Continental crust. • An ocean trench forms and coastal volcanoes are created. Head on Collision!!! Converging plates • Two Continental plates collide into one another. • The edges push upward and create mountain ranges. • Ex. Applachians, Himalayas, Rocky mountains. Oceanic Collision An Island is born. • Convergent boundaries occur between two oceanic crust. • A deep ocean trench is created and lava is pushed to the surface to form islands. • Known as “Hot Spots”. Ex. Hawaiian Islands. On shaky ground. • Plate boundaries known known as Transform fault occur when two plates grind away at one another. • The San Andreas fault line is an example of a transform fault. Continental Drift The theory of… • 1912 German Alfred Wegener proposed the hypothesis called continental drift. • Said that all the continents formed a single land mass called Pangaea • According Wegener, 200 million years ago Pangaea began to break up. What proof is there… Putting the pieces together. • Wegener based his theory on fossil remains that were found two different continents. 270 m.y.a. • Age and type of rocks in the coastal regions of S. America & Africa were identical. • Coal deposits in N.America, Europe and Siberia are very similar. Sea-Floor Spreading • 1947- Map of the Mid0Atlantic Ocean ridge, a mountain chain underwater that wraps around the world. • The age of the ocean floor is very young compared to the continental crust. Sea-floor Spreading What proof is there? • PALEOMAGNETISM OF THE OCEAN FLOOR. • When magma cools the metallic materials in the magma points to the magnetic north. • Sections of the ocean floor on both sides of the ridge orient in the opposite directions that suggest that there are paleo-shifts. What fuels this process? The Earth’s engine. • Plate tectonics is driven by convection currents that are found within the earth’s athenosphere. • The athenosphere is the layer under the crust that consist of liquid like magma that allows the crust to float on top like ice on a lake. What fuels this process? The Earth’s engine cont. • Other possibilities to plate tectonics are; • Ridge push- At the mid-atlantic ocean ridge the lithosphere is higher than where it sinks into the asthenosphere. It actually pushes the plates downhill. • Slab pull- Because oceanic lithosphere is denser than continental lithosphere the edges of the oceanic plates sink into the asthenosphere pulling the rest of the tectonic plates. Reviewing the “plate theory” • Boundaries between tectonic plates include; convergent, divergent and transform. • Wegener hypothesized that continents drifted apart from one another and did so in the past. • As tectonic plates separate, the sea-floor spreads apart and magma fills in the new gap. • Magnetic reversals is one way to measure the age and movement of the tectonic plates.