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