Download plate tectonics review

Continental Drift, Seafloor
Spreading & Plate
Tectonics
Standard 3
(pink test review packet)
Continental Drift
• Earth’s continents were once joined as
single landmass; broke apart and
continents drifted to present position
• Pangaea: supercontinent (break up ~ 200
mya)
• Wegner
• Not accepted - lack of mechanism for the
movement of continents (why and how)
Evidence for Continental Drift
1. Jigsaw puzzle fit of continents (S.A. &
Africa)
2. Rock formations on different continents –
same age, similar structure
3. Fossils of land dwelling animals on
different continents
4. Climate – coal beds (form in humid
swamps) found in Antarctica & tropical
plants
Seafloor Spreading
• New oceanic crust forms at mid-ocean
ridges
• Destroyed at subduction zones (deepsea trenches)
• Magma rises, forced upwards, lava
fills in ridge, hardens and new seafloor
moves away from the center of the
ridge.
Evidence for Seafloor Spreading
• Discovery of mid-ocean ridges
• Seafloor youngest at mid-ocean ridges
• Magnetic pattern is the same on both
sides of the ridge (mirror image)
• Hess
• Technology: Sonar (uses sound waves)
Theory of Plate Tectonics
• Earth’s crust and rigid upper mantle are
broken into tectonic plates
• Movement of plates creates most
volcanoes and major mountain ranges
• Movements cause earthquakes
• Plates move because of Convection in
the mantle
Types of crust/plates
• Continental Crust
– Older
– Lighter
– Granite
– 30 miles thick
• Oceanic Crust
– Younger
– Denser
– Basalt
– 5 miles thick
Plate Boundaries
•Divergent
•convergent
•transform
Divergent
– Plates move away from each other
– Most found on seafloor (mid-ocean ridges)
– Found on continental crust – stretches crust
to form a rift valley (African Rift Valley)
– Shallow earthquakes
Convergent
• Plates move towards each other
• Crash or collide
• 3 types based on type of crust
Convergent Boundaries: plates
converge/collide
• Continental – continental
– high mountain ranges
– Himalayas
• Continental – oceanic
– volcanic mountain ranges on land, deep-sea trenches
– Cold more dense plate sinks
– Andes, Cascades
• Oceanic – oceanic
– volcanic islands, deep-sea trenches
– Colder, denser plate sinks
– Mariana Island, Japan
Transform Boundaries
• Two plates slide past each other
• Example – San Andreas fault
Mantle Convection
• Convection: hot less dense material
rises & cold, denser material sinks
• Magma rises because it is less dense than
surrounding rock & it forces itself upwards
• Driving force of plate tectonics
HOT SPOTS
• Some volcanoes form over hot spots
• As tectonic plate moves chain
volcanoes form
• Hawaiian Islands – Kilauea located over
hot spot
• Yellowstone located over hot spot