Looking at the world map, Looking at the world map, what do you notice about the what do you notice about the

shape of the continents?shape of the continents?

Jot down your ideas on your paper…

The thing is…the world didn’t The thing is…the world didn’t always look like this! It used to always look like this! It used to

look like this:look like this:

How is this possible?!?!?How is this possible?!?!?

The continents have shifted their position over geologic time

Continental Drift TheoryContinental Drift Theory

At one time all land masses were connected into one piece called Pangaea

o Pangaea began to split apart 200 million years ago

o DiagramNorth America

Laurasia GreenlandEurasia

PangaeaAfricaWest G. S.America

GondwanalandAntarctica

East G. AustraliaIndia

o The continents are like packages on the seafloor conveyor belt

ContinentsContinents

o High probability that the continents fit together

EvidenceEvidence

o Minerals, fossils, and mountains on now different continents match if the continents were together

EvidenceEvidence

o Glaciation patterns indicate a common ice cap at the South Pole

EvidenceEvidence

o PaleomagnetismPaleomagnetism (magnetism of old rocks) indicate a common pole if the continents were all connected

EvidenceEvidence

Seafloor Spreading Theory:

• Ocean floors are moving like broad conveyor belts

• New ocean floor crust is being created at the mid-ocean ridges

Convection currents within the mantle

The up-welling leg of the current creates a divergent boundary which produces mid-ocean ridges

What causes this?What causes this?

The down-welling leg of the current creates one type of convergent boundary that results in trenches and a subduction zone

o Mid-ocean ridges are warmer than surrounding ocean floors

o Active volcanoes on ridges, earthquakes on ridges

o Mid-ocean ridge rocks are younger than surrounding ocean floor rocks

o Mid-ocean ridge volcanoes are younger than volcanoes further away

What evidence do we have to What evidence do we have to support this idea?support this idea?

o Ocean floor sediments are thin on the ridges and get thicker as the distance from the ridges increase

o Polar reversal magnetism proves that the ocean floor is moving away from the ridges

What evidence do we have to What evidence do we have to support this idea?support this idea?

Atlantic Ocean – 2-3 2-3 cm/year

South Pacific Ocean – 15-1815-18 cm/year

Speed of SpreadingSpeed of Spreading

The lithosphere is divided into a number of large and small plates and the plates are floating on the mantle

Plate Tectonics TheoryPlate Tectonics Theory

Lithosphere = the Earth’s crustcrust plus the upper portion of the mantlemantle layer

Boundaries between Boundaries between Tectonic PlatesTectonic Plates

Get Out the Following Things:Get Out the Following Things:

• Plate Tectonic Notes

• Plate Tectonic Directed Reading

• MAKE SURE YOU HAVE YOUR TEXTBOOK!!!

Plate BoundariesPlate Boundaries

Divergent boundary: Divergent boundary: o Plates are moving away

from each othero Mid-ocean ridges are

created and new ocean floor plates are created

Plate BoundariesPlate Boundaries

Divergent boundary: Divergent boundary:

Leif the Lucky Bridge Bridge between continents in Reykjanes peninsula, southwest Iceland across the Alfagja rift valley, the boundary of the Eurasian and North American continental tectonic plates.

Convergent BoundaryConvergent Boundary: plates are moving toward each other and are colliding (3 types)

• Create subduction zones, trenches

• Create near coast volcanoes

When Ocean Plates Collide When Ocean Plates Collide with Continental Plateswith Continental Plates

When ocean plates collide with When ocean plates collide with other ocean platesother ocean plates

Island arcs are created (a pattern of volcanic islands

created from a subduction zone that is located off the coast)

• MountainMountain rangesranges are created

• (example: Himalayan Mountains)

When a continental plate collides When a continental plate collides with another continental platewith another continental plate

Himalayan MountainsHimalayan Mountains

Mountain Formation Video Clip

Transform BoundaryTransform Boundary

Plates are neither moving toward nor away from each other, they are moving past one another.

Transform BoundaryTransform Boundary

The plates may move in opposite directions or in the same directions but at different rates and frequent earthquakes are created (example: San Andreas Fault)

San Andreas FaultSan Andreas Fault

o Noo Plates are destroyed as fast as

they are created (2 ways)o Plates may be subducted and

melted or may push be pushed upward to form mountains

So is the Earth getting bigger?So is the Earth getting bigger?

Plate Tectonic ReviewPlate Tectonic Review