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. Plant/ Animal Evidence

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

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

So the Continents Move? Theory lead to Plate Tectonics Plate Tectonics now is able to explain why, how, and where the plates will move. 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 Crust is broken up into large segments called plates

Asthenosphere – lower mantle

Plates and Layers Plates are made out of the Lithosphere “Float” on Asthenosphere Acts like a liquid and a solid Continental Plate Oceanic Plate 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: Mid Atlantic Ridge – magma coming up creating new rock in center

Forming a Divergent Boundary To view this animation, click “View” and then “Slide Show” on the top navigation bar.

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

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

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