Continental Drift and Plate Tectonics The Origins Alfred

Continental Drift and Plate Tectonics

The Origins ¢Alfred Wegener developed a theory that the continents once formed a giant supercontinent

Evidence of Continental Drift ¢ Jigsaw puzzle like

Evidence ¢ Plant and animal fossils found on several different continents were quite similar. ¢ Physically impossible for these organisms to have traveled across the ocean ¢ Compelling evidence that the two continents were once joined.

Evidence ¢ Broad belts of rocks in Africa and South America are the same type ¢ Mountain belts match up

Evidence ¢ Glacial striations on rocks - cuts from when glaciers move match up across the world

So the Continents Move? ¢ Theory lead to Plate Tectonics l Plate Tectonics now is able to explain why, how, and where the plates will move. l Continental Drift only knew that plates moved, but DID NOT KNOW HOW

Projected Future

¢Crust- hard solid ¢Mantle- soft solid ¢Outer Core- liquid ¢Inner Core- solid

Earth’s Structure ¢ Lithosphere – crust and upper mantle l. Crust is broken up into large segments called plates

¢Asthenosphere – lower mantle

Plates and Layers Plates are made out of the Continental Plate Lithosphere Oceanic Plate ¢ “Float” on Asthenosphere ¢ Acts like a liquid and a solid ¢ Lithosphere Asthenosphere Mantle

Inside the Mantle ¢ ¢ Because the earth is very hot inside, a current of heat flows from the core to the crust. This is called convection current (heat rises, cools, then sinks down)

Convection Currents Explains how plates move ¢ Wegner could never explain this!! ¢

Plate Movements Plates are sitting onto of the mantle and “float”. ¢ They either push together, pull apart, or grind against each other. ¢

Divergent Plate Two plates push apart ¢ Creates sea floor spreading, leading to the formation of new crust ¢ SEA FLOOR SPREADING: ¢ l Mid Atlantic Ridge – magma coming up creating new rock in center

Forming a Divergent Boundary

Where is the youngest rock? Where is the oldest rock? Is there is a pattern?

What Do the Volcanoes Show? 40 myo 30 myo km 75 km 50 km 25 km 50 75 km 20 myo

Convergent Boundary ¢ ¢ Plates colliding together Ocean-Ocean : Volcanoes Ocean – Continental : Volcanoes Continental – Continental: Mountains

Convergent Boundary

Convergent Boundary

Transform Boundary Plates slide past each other ¢ Creates large breaks in rock ¢ Earthquakes ¢ Examples: San Andreas Fault ¢