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. 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 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.