Chapter 10 Plate TectonicSection 1 Continental Drift
I. Evidence of Continental Drift
A. Pangaea
1. Continental drift – a hypothesis that the continents have
moved slowly to their current locations
2. Pangaea –means “all land”
a. All continents were once connected as one large landmass
b. Broke apart 200 million years ago
B. Fossil Clues
1. Puzzlelike fit of continents
2. Fossils of Mesosaurus found in South America and Africa
D. A Widespread Plant - Glossopteris plant fossils
found in Africa, Australia, India, South America, and Antarctica
E. Climate Clues
1. Fossils of warm-weather plants found on islands in Arctic Ocean
2. Evidence of glaciers found in South America, Africa, India, and
Australia
F. Rock Clues – similar rock structures are found on different
continents
Section 2 Seafloor Spreading
I. Mapping the Ocean Floor
A. Scientists used sound waves on moving ships to discover underwater
systems of ridges and valleys in the oceans
B. The Seafloor Moves
1. Harry Hess – suggests theory of seafloor spreading
2. How seafloor spreading works
a. Hot, dense material below Earth’s crust rises upward at the
mid-ocean ridges
b. It flows sideways, carrying seafloor away from the ridge in
both directions
c. Magma moves upward and flows from the cracks
d. Magma cools and forms new seafloor
Section 3 Theory of Plate Tectonics
I. Plate Tectonics
A. Plate Movements
1. Plate tectonics – Earth’s crust and part of the upper mantle are
broken into sections called plates
2. Plates move on plasticlike layer of the mantle
B. Composition of Earth’s Plates
1. Lithosphere – crust and part of the upper mantle
2. Asthenosphere – plasticlike layer below the lithosphere
II. Plate Boundaries
A. Plates Moving Apart – divergent boundaries
B. Plates Moving Together – convergent boundaries
1. Oceanic plate converges with less dense continental plate
2. Subduction zone – where oceanic plate goes down into the
mantle
3. Rock melts around the subducting slab
4. Newly formed magma is forced upward and forms volcanoes
C. Where Plates Collide
1. Two continental plates collide and crumple up forming mountain
ranges
2. Earthquakes are common
3. Volcanoes don’t form – little or no subduction
D. Where Plates Slide Past Each Other
1. Transform boundary
2. Two plates slide past one another
a. Move in opposite directions
b. May move in same direction at different rates
3. Earthquakes occur
4. San Andreas fault in California
III. Causes of Plate Tectonics
A. Convection Inside the Earth
1. The cycle of heating, rising, cooling and sinking of material
in the mantle is thought to be the force behind plate tectonics
2. Differences in density cause hot, plasticlike rock to be forced
upward toward the surface
B. Moving Mantle Material
1. All hypotheses use convection in some way
2. Transfer of heat inside the Earth provides energy to move plates
IV. Features Caused by Plate Tectonics
A. Normal Faults and Rift Valleys
1. Tension forces, forces that pull apart, can stretch Earth’s crust
2. Large blocks of crust break and tilt
3. A fault forms
4. Rock layers are moved out of place
5. Mountain ranges can form – fault-block mountains
6. Rift valleys and mid-ocean ridges form where Earth’s crust
separates
B. Mountains and Volcanoes
1. Where continental plates converge – mountain ranges form
a. Himalayas
b. Appalachians
2. When two oceanic plates converge – denser plate is forced
beneath the other plate
– curved chains of volcanic islands form above sinking plate
3. When an oceanic plate and a continental plate collide – the
oceanic plate slides under the continental plate
a. Crust thickens to form mountain ranges
b. Volcanoes are typically formed
C. Strike-Slip Faults
1. Two plates slide past each other
2. Rocks on opposite sides of the fault move in opposite directions
or in the same direction at different rates
3. Vibrations are generated inside the Earth that are felt as
earthquakes
V. Testing for Plate Tectonics
A. Studied magnetic characteristics of rocks on seafloor
B. Studied volcanoes and earthquakes
C. Now scientists use lasers and satellites – can measure movements
as little as 1 cm per year
I. Evidence of Continental Drift
A. Pangaea
1. Continental drift – a hypothesis that the continents have
moved slowly to their current locations
2. Pangaea –means “all land”
a. All continents were once connected as one large landmass
b. Broke apart 200 million years ago
B. Fossil Clues
1. Puzzlelike fit of continents
2. Fossils of Mesosaurus found in South America and Africa
D. A Widespread Plant - Glossopteris plant fossils
found in Africa, Australia, India, South America, and Antarctica
E. Climate Clues
1. Fossils of warm-weather plants found on islands in Arctic Ocean
2. Evidence of glaciers found in South America, Africa, India, and
Australia
F. Rock Clues – similar rock structures are found on different
continents
Section 2 Seafloor Spreading
I. Mapping the Ocean Floor
A. Scientists used sound waves on moving ships to discover underwater
systems of ridges and valleys in the oceans
B. The Seafloor Moves
1. Harry Hess – suggests theory of seafloor spreading
2. How seafloor spreading works
a. Hot, dense material below Earth’s crust rises upward at the
mid-ocean ridges
b. It flows sideways, carrying seafloor away from the ridge in
both directions
c. Magma moves upward and flows from the cracks
d. Magma cools and forms new seafloor
Section 3 Theory of Plate Tectonics
I. Plate Tectonics
A. Plate Movements
1. Plate tectonics – Earth’s crust and part of the upper mantle are
broken into sections called plates
2. Plates move on plasticlike layer of the mantle
B. Composition of Earth’s Plates
1. Lithosphere – crust and part of the upper mantle
2. Asthenosphere – plasticlike layer below the lithosphere
II. Plate Boundaries
A. Plates Moving Apart – divergent boundaries
B. Plates Moving Together – convergent boundaries
1. Oceanic plate converges with less dense continental plate
2. Subduction zone – where oceanic plate goes down into the
mantle
3. Rock melts around the subducting slab
4. Newly formed magma is forced upward and forms volcanoes
C. Where Plates Collide
1. Two continental plates collide and crumple up forming mountain
ranges
2. Earthquakes are common
3. Volcanoes don’t form – little or no subduction
D. Where Plates Slide Past Each Other
1. Transform boundary
2. Two plates slide past one another
a. Move in opposite directions
b. May move in same direction at different rates
3. Earthquakes occur
4. San Andreas fault in California
III. Causes of Plate Tectonics
A. Convection Inside the Earth
1. The cycle of heating, rising, cooling and sinking of material
in the mantle is thought to be the force behind plate tectonics
2. Differences in density cause hot, plasticlike rock to be forced
upward toward the surface
B. Moving Mantle Material
1. All hypotheses use convection in some way
2. Transfer of heat inside the Earth provides energy to move plates
IV. Features Caused by Plate Tectonics
A. Normal Faults and Rift Valleys
1. Tension forces, forces that pull apart, can stretch Earth’s crust
2. Large blocks of crust break and tilt
3. A fault forms
4. Rock layers are moved out of place
5. Mountain ranges can form – fault-block mountains
6. Rift valleys and mid-ocean ridges form where Earth’s crust
separates
B. Mountains and Volcanoes
1. Where continental plates converge – mountain ranges form
a. Himalayas
b. Appalachians
2. When two oceanic plates converge – denser plate is forced
beneath the other plate
– curved chains of volcanic islands form above sinking plate
3. When an oceanic plate and a continental plate collide – the
oceanic plate slides under the continental plate
a. Crust thickens to form mountain ranges
b. Volcanoes are typically formed
C. Strike-Slip Faults
1. Two plates slide past each other
2. Rocks on opposite sides of the fault move in opposite directions
or in the same direction at different rates
3. Vibrations are generated inside the Earth that are felt as
earthquakes
V. Testing for Plate Tectonics
A. Studied magnetic characteristics of rocks on seafloor
B. Studied volcanoes and earthquakes
C. Now scientists use lasers and satellites – can measure movements
as little as 1 cm per year