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.

EvidenceBroad 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 TectonicsPlate 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

Crust- hard solidMantle- soft solidOuter Core- liquidInner Core- solid

Earth’s StructureLithosphere – 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.

Projected Future

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

Where is the youngest rock? Where is the oldest rock?

Is there is a pattern?

25 k

m

25 k

m

What Do the Volcanoes Show?

20 myo

50 k

m

50 k

m

30 myo

75 k

m

75 k

m

40 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