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Why does Earth have mountains?
Where do they come from? Why are there ocean fossils at the top of the Himalayas? Why does California have Earthquakes? Where do volcanoes come from?
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Plate Tectonics Chapter 8
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Alfred Wegener Continental Drift Evidence
Wegener thought whole sections of the crust moved Evidence Shape of Continents Rock Evidence Same mountains on different continents Fossil Evidence Same fossils on different continents
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Continental Drift Africa and South America look like they fit together
Click on the picture to see the evidence Ancient Mountain Belts Ancient Sand Dunes Fossil Evidence
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Continental Drift Fossil Evidence
- Same fossils found on different continents Mesosaurus Lystrosaurus Glossopteris Cynognathus
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Continental Drift What the hypothesis was missing was the HOW?
Alfred Wegener proposed that the continents were moving on a more fluid layer under the crust that could possibly be moving due to internal heat . . . He had no way to prove it!
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He was right!. . .well mostly
He died before his hypothesis was accepted as a theory. New technology allowed scientists to examine the structure of Earth They found that the lithosphere was moving due to Earth’s internal heat. This developed into the theory of Plate Tectonics
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Who came up with continental drift?
Alfred Wegener Sir Isaac Newton Copernicus Alfred Hitchcock
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What evidence did Alfred Wegener use to support continental drift?
Shape of continents Rock evidence Fossil evidence All of the above
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Why could Alfred Wegener not prove continental drift?
He could not prove the land moved He could not prove how the land moved He did
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Where do most earthquakes and volcanoes occur?
In the middle of plates Along coasts Along mountain ranges Along plate boundaries
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Plate Tectonics Evidence
Continental Drift (continents fit, fossils, rocks) New Evidence Location of Earthquakes and Volcanoes (p173) Magnetism of the ocean floor (p174) Age of the ocean floor (p175)
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Plate Tectonics Evidence
Earthquakes and Volcanoes: Most earthquake and volcano activity happen along plate boundaries. Plates are moving apart, moving together, or sliding past one another. This creates earthquakes Where plates move apart and come together magma is brought to the surface This creates volcanoes
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Plate Tectonics World Earthquakes
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See page 712 to view direction of plate movement
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Plate Tectonics Evidence
Magnetism of the Ocean Floor (see page 174) Mid-ocean Ridges are places where NEW rock is forming. These rocks contain magnetic minerals (minerals with iron) they point to the north pole The north pole can flip with the south pole These minerals flip too. This is called a magnetic reversal.
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Plate Tectonics Seafloor Magnetism Video
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Plate Tectonics Evidence
Age of the Ocean Floor New rock is formed at a mid-ocean ridge or spreading center These are formed in the middle of the ocean The rock gets older as you move away from the ridge The ocean floor is not that old because it subducts under continents The oldest ocean floor is ~180 million years old
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Plate Tectonics Age of the ocean floor
oldest youngest
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Crust + Upper Mantle = Lithosphere (solid)
Earth’s Structure Crust + Upper Mantle = Lithosphere (solid) Asthenosphere “fluid” portion of the mantle Mantle - Solid Outer Core – Liquid Inner Core – Solid Heat comes from radioactive material in the core
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Mantle Convection
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Composition Thick Low Density Thin High Silica High Density Floats
Low Silica Sinks
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3 Types of Plate Boundaries:
Divergent Convergent Transform
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Divergent Boundary Sea floor spreading
Large continents begin to crack and split apart The gaps fill with water Small seas become oceans The mid ocean ridge continues to produce new crust
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Divergent Boundary Characteristics
2 plates are moving apart Shallow Earthquakes Magma comes to the surface and cools Basalt rock forms Dense and dark in color Creates a Mid-Ocean Ridge Rift valleys form in the center Examples: Mid Atlantic Ridge and East Pacific Rise
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Divergent Boundary How?
The plates are pulled apart by convection currents in the mantle below Caused by heat released from natural radioactive processes At mid-ocean ridges molten rock from below rises up to fill the gap with new basaltic rock
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Let’s Draw a Divergent Boundary
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Using the Map on page 712-713 Highlight the Divergent Boundaries
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True or False: The magnetic polarity of Earth changes
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Magnetic stripes of oceanic crust proves…
Earth is rotating One piece of evidence to prove plate movement That the rocks are very old
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Seafloor rock gets older as…
You move away from the mid-ocean ridge As you move toward the mid-ocean ridge As you move into the mid-ocean ridge
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The Lithosphere is… The crust and the upper mantle
Another word for mantle The crust and asthenosphere The inner core
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Which layers of the Earth are solid?
Inner Core Outer Core Mantle Crust All of the above 1, 3, and 4
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Which layers of the Earth are liquid?
Inner core Outer core Mantle Asthenosphere Crust All of the above 2 and 4
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A divergent boundary is where plates…
Move apart Come together Slide past each other
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All divergent boundaries eventually form…
Mountains Oceans Continents The moon
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3 Types of Plate Boundaries:
Divergent Convergent Transform
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Convergent Boundaries
2 plates are moving together Ocean-Ocean Ocean-Continent **Deep Earthquakes Continent-Continent **Earthquakes Subduction Zone Volcanoes Form Creates Mountain Belts NO VOLCANOES
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Convergent Boundaries -Subduction-
Ocean-Ocean or Ocean-Continent The denser plate always subducts Volcano Forms Subducting Plate more dense Plate Melts
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Ocean – Continent Subduction
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Ocean – Continent Subduction
The ocean plate always subducts because it is more dense. Continental volcanic arcs or a mountain chain of volcanoes form on the continental plate. Examples: Cascades of N. America Andes of S. America
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Ocean – Ocean Subduction
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Ocean – Ocean Subduction
The denser ocean plate always subducts because it is more dense. Volcanic island arcs or chains of volcanic islands form on the OTHER OCEAN plate. Examples: Aleutian Islands, Alaska Mt Pinatubo, Philippines Mt Fuji, Japan
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Lets Draw a Subduction Boundary
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Collision Boundary
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Collision Boundary
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Convergence of India
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Collision Boundary There is NO SUBDUCTION because both plates are continental and have low density. They buckle up forming mountains (not volcanoes) Examples: Himalayas, India/Asia
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Highlight and Label the Major Convergent Boundaries
Using the Map on page Highlight the Divergent Boundaries
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What tectonic plate ALWAYS subducts?
Oceanic plate Continental plate Both Neither
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What convergent boundary can form volcanoes?
Ocean – ocean Ocean – continent Continent – continent All of the above 1 and 2 3 and 4
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What is an example of a continental volcanic arc?
Hawaii Cascades Himalayas Andes 2 and 4 All of the above
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What is an example of a volcanic island arc?
Hawaii Mt. Pinatubo Cascades Himalayas Mt. Fuji 2 and 5 All of the above
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What plate subducts in a collision boundary?
The more dense continental plate Both continental plates Neither continental plate
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What is an example of a collision boundary mountain range?
Hawaii Mt. Pinatubo Cascades Himalayas Mt. Fuji 1, 2, and 4 All of the above
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3 Types of Plate Boundaries:
Divergent Convergent Transform
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Transform Boundaries Occur when 2 plates are sliding past one another
Ocean – Ocean Ocean – Continent Continent - Continent No Volcanic Activity Examples San Andreas Fault Along Ocean Floor ** Earthquakes!
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Let’s Draw a Transform Boundary
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Highlight and Label the Major Transform Boundaries
Using the Map on page Highlight the Transform Boundaries
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