Plate TectonicsPlate Tectonics

Plate TectonicsPlate Tectonics is a is a theory that describes theory that describes

the formation, the formation, movements, and movements, and

interactions of Earth’s interactions of Earth’s plates.plates.

Alfred Wegener, a Alfred Wegener, a German meteorologist, German meteorologist, proposed a hypothesis proposed a hypothesis called called Continental DriftContinental Drift

in 1912.in 1912.

Continental DriftContinental Drift supposed that the supposed that the

continents have moved, continents have moved, or drifted, from one or drifted, from one

location to another over location to another over long periodslong periods of time. of time.

Continental DriftContinental Drift supposed that the supposed that the continents have continents have

moved, or driftedmoved, or drifted, from , from one location to another one location to another

over long periodsover long periods of of time.time.

Wegener based his idea Wegener based his idea on the following on the following observations:observations:

The continents had similar shapes.

The same fossils were found in South America and Africa.

Similar rock formations were found in South America and Africa.

Climate Change: Areas once covered in glaciers are now in warmer climate zones.

Wegener’s idea could not explain how the continents moved.

The Theory of Plate Tectonics suggests that the continents are part of the

lithospheric plates.

Evidence for this:

Volcano, Earthquake, and Mountain Belts are located

along plate boundaries.

The ocean floor gets older away from a mid-ocean

ridge.

The rock record shows that the magnetic field of the

Earth has reversed many times.

Types of Plate Boundaries

Divergent Boundary

Rift Valleys and Mid-Ocean Ridges

Convergent Boundary

Deep Sea Trenches, Subduction Zones, and Mountain Ranges

Convergent (2 Types)

Convergent Subduction

More Dense (Oceanic Crust)

Less Dense (Continental or Oceanic Crust)

Convergent Collision

Equal Density Continental Crust

Transform (Strike-Slip) Boundary

San Andreas FaultDivision between North American

and Pacific Plates

San Andreas FaultDivision between North American

and Pacific Plates

North American Plate

Pacific PlatePac

ific Pla

te

North A

merica

n Plat

e

Types of Plate Boundaries

Causes of Plate Causes of Plate MovementMovement

3 Hypotheses3 HypothesesMantle ConvectionMantle Convection

Ridge PushRidge PushSlab PullSlab Pull

Mantle Convection: The mantle moves Mantle Convection: The mantle moves the plates along as it convects (heats the plates along as it convects (heats

from below). Mantle Convection from below). Mantle Convection Animation #2Animation #2

Ridge PushRidge Push: The : The accumulating magma at a accumulating magma at a mid-ocean ridge “pushes” mid-ocean ridge “pushes”

material away.material away.

Slab PullSlab Pull: When a plate : When a plate subducts, it pulls the rest of subducts, it pulls the rest of

the plate with it.the plate with it.