Download Section 17.3 Theory of Plate Tectonics

Name _______________________Period____
NOTE OUTLINE: Chap 17 Plate Tectonics
Objectives
1. Describe early evidence that led people to suggest that Earth’s continents may have once been
joined.
2. Discuss evidence of continental drift.
3. Explain why continental drift was not accepted when it was first proposed.
4. Summarize the evidence that led to the discovery of seafloor spreading.
5. Describe the uses of magnometers and sonar.
6. Explain the significance of magnetic patterns on the seafloor.
7. Explain the process, cause, features and evidence of seafloor spreading.
8. Explain the theory of plate tectonics.
9. Compare & contrast the 3 types of plate boundaries and the features, location, & direction of
movement of each. (Features include: subduction, trenches, ridges, mountains, islands)
10. Explain the process of convection.
11. Summarize how convection in the mantle is related to the movements of tectonic plates.
12. Compare & contrast the processes of ridge push & slab pull.
13. Miscellaneous vocabulary: Pangea, early mapmakers, Wegener
Sec 17.1 Drifting Continents – Earliest Evidence
1. Early mapmakers noted that the ___________________of continents appeared to ______________
like a ________________________, especially the southern continents; South America and Africa.
Alfred Wegener:
1. Alfred Wegener proposed hypothesis of _________________________________
2. Continental Drift theory: ______ continents were originally joined as a single landmass
called _________________ and began to break up 200 million years ago, and the process is
STILL occurring.
3. Wegener’s evidence for continental drift went beyond the “puzzle fit” the map-makers had seen.
Wegener collected evidence to support his ideas from:
A. Rocks
B. Fossils
C. Climatic Data
4. Evidence from Rocks: Similar rock types between:
A. _____________________mountains in _______ & rocks in _________________
B. __________________________ & _________________________
747142162
-1-
6/18/2017
5. Evidence from Fossils: Similar fossils and plants have been found on widely separated continents:
A. Kannemeyerid & Labyrinthodonts were ___________________ animals that could
NOT have ________________________
B. Mesosaurus: ____________________ reptile that could not have crossed the ocean
C. Glossopteris: ________ found on many continents that have now have _____ climates
 Continents must have been joined & had a ______________________ climate to grow
the fern
 Antarctica must have been closer to the _______________ to have a ____ enough
climate to grow the fern
6. Ancient Climatic Evidence
A. _________deposits have been found in Antarctica

It forms from dead swamp plants. Swamps only occur in an area that is _________
 This indicates that Antarctica was once ______________________ and closer to the
______________________
B. ________________deposits in Africa, India, South America, and Australia

This suggests that these areas were closer to the __________________ at one time
7. Problems With Wegener’s Continental Drift Theory caused it to be rejected in the early 1900’s
because of these 2 “flaws”:
A. Wegener couldn’t explain what caused the continents to ____________
B. Wegener couldn’t explain how the continents could move without ____________________
C. Ideas about the ocean floor were wrong until the mid-1900’s. Scientists thought the seafloor was flat,
older than continents, and unchanging-ALL WRONG
New Discoveries and Ideas about the Seafloor (Sec 17.2 Seafloor Spreading)
1. Sonar – new technology. Big advancement.
A. Calculated the distance to the seafloor using the _________ it took for reflected
____________________ to return
2. Magnetometer: Measures small changes in ___________________ fields
A. Used to make maps of the _____________________ fields in ____________on the seafloor
3. Ocean floor topography
A. Ocean______________contain the ______________mountain range on Earth
_______________________________ occur along the ridges
B. Deep-sea _______________ are narrow & elongated depressions w/very steep sides
Deepest trench: Marianna trench is over 11km deep
747142162
-2-
6/18/2017
4. Ocean rocks & sediments
A. Rocks near the ridges are the ___________________________, age increases with distance
from the ridge
B. Oceanic rocks are much ____________________ than continental rocks
C. Oceanic sediments are _____________________ than continental sediments
D. Thickness of sediments __________________with distance from the mid-ocean ridges
5. Paleomagnetism: magnetic record of rocks containing __________________
A. Basalt contains iron minerals which get “stuck” pointing towards Earth’s
_______________________ as it cools and hardens
B. The iron minerals show a pattern of ____________________________which indicate a
change in Earth’s magnetic field
6. Seafloor spreading theory SUMMARY: New ocean crust is formed at ocean ridges & is destroyed
at deep-sea trenches
A. Proposed by Harry Hess
B. Magma is ___________ & ________ dense at the midocean ridge, so it fills the gap in the
ridge
C. Magma in the gap cools, forming new ocean floor
D. More & more magma rises & hardens, forcing the previous rock to move away from the ridge
E. Therefore, _______________ rock is near the ridge and age ______________ farther from
the ridge
F. Theory provided answers to the 2 flaws of Wegener’s continental drift hypothesis
Seafloor spreading caused the landmasses to move
Landmasses didn’t shatter because they weren’t plowing through the ocean
crust. Rather, the ocean floor & continents moved together.
Section 17.3 Theory of Plate Tectonics
 Theory states that the Earth’s crust & ridged upper mantle are broken into enormous slabs called
plates.
 Plates move in different directions and at different rates.
 Plate Boundaries = Where tectonic plates interact
Plate boundaries: 3 main types
1. Divergent
2. Convergent
3. Transform
747142162
-3-
6/18/2017
1.
Divergent Boundaries: Plates move ____________________
 There are 2 subtypes of divergent boundaries, depending on their location:
A. Mid-Ocean Ridge forms if the divergent boundary is underwater
 Mid-Ocean Ridge is a long mountain chain with volcanoes
 Causes the ocean basin to widen.
http://geology.com/nsta/divergent-plate-boundaries.shtml
B. Rift Valley forms if the divergent boundary is on land
 As the continent is torn farther and farther apart, the rift valley gets deeper and
deeper.
 It may eventually fill with water and become an ocean
 Example Rift Valley Locations: Iceland & East Africa
C. BOTH types of divergent boundaries add (create) new crust
D. Divergent boundaries widen ocean basins and lengthen/widen earth’s surface
 The Atlantic Ocean is widening an average of 2-3cm / year.
E. Volcanoes and earthquakes are common along both rift valleys and mid-ocean ridges
F. Explains why young rock is in the middle of the ocean and older rock near the continents.
2.
Convergent Boundaries: Plates _________________ & move ______________________
A. Subduction MAY occur: One plate ________________________________ the other
 _______________________________ crust material
 Due to differences in density
 May create deep-sea trenches, volcanoes & volcanic islands – depending on where
they form
747142162
-4-
6/18/2017
3 subtypes of Convergent Boundaries
1. 1st subtype of Convergent: Oceanic meets Oceanic
http://geology.com/nsta/convergent-plate-boundaries.shtml
A. Subduction________________
 The _____________ & _______________ oceanic plate descends below the
_________________ oceanic plate
B. Forms deep-sea ____________, island ________, ______________ & ___________
earthquakes
C. Example locations:
 Mariana Trench & Islands
 Aleutian Islands near Alaska
 Japan & Philipines
A. 2nd Subtype of Convergent: Oceanic meets Continental
http://geology.com/nsta/convergent-plate-boundaries.shtml
i.
Subduction___________________
 __________ocean plate descends below the ________________ continental plate
 Ocean plates are dense because they are made of ___________________
 Continental plates are less dense because they are made primarily of __________
747142162
ii.
Forms ________________________ along the edge of continents
iii.
Mountain ranges, volcanoes, deep focus earthquakes may occur along the continental
iv.
edge ______________________________________
Example locations: Peru-Chile trench & Andes Mountains along western
edge of ____________________________
-5-
6/18/2017
B. 3rd subtype of Convergent: Continental meets Continental
http://geology.com/nsta/convergent-plate-boundaries.shtml
i.
Subduction ____________________________
 Both continental plates are too ___________________ due to
__________________
 Therefore, there is ____________________________________________
3.
ii.
______________ mountain ranges, extremely folded
iii.
Earthquakes present
iv.
Example location: ____________________________
Transform Boundaries: 2 plates __________________________________ past each other
A. Crust is NEITHER consumed or created, only deformed or fractured
B. Creates long __________________ & ____________________ earthquakes
i.
Fault = ________________ in Earth’s crust along which movement occurs
C. Can move __________________directions, OR the same direction at different ___________
D. Example locations: _____________________________ fault. Most are along ocean ridges
747142162
-6-
6/18/2017
Section 17.4 Causes of Plate Motions
Convection: The transfer of thermal energy by the movement of heated matter
1. Warms, _________________, and becomes _____________________ & ____________
2. __________________________ material sinks due to gravity
3. Forms a cycle, or _____________________________
Mantle Convection Currents in the Asthenosphere:
1. ________________in the aesthenosphere is thought to cause the plate movements
A. Aesthenosphere is a ____________________________ of the mantle that ________ &
allows the plates to move
B. Hot mantle material is less dense & rises, as it cools it sinks again
2. Rising part of current occurs at _________________________boundaries
A. Causes upward & lateral forces that __________________________________
B. As plates separate, rising ________________ cools & forms new ___________________
3. Sinking part of the current occurs at _____________________ boundaries, pulling the plate material
down
A. Sometimes forms ________________________
747142162
-7-
6/18/2017
Bellringer #1:Review of Section 17.1 & Video
1. What theory suggests that South America and Africa were once part of a larger continent that
broke and moved apart?
2. Who was the German scientist who proposed the most famous version of this theory?
3. List 3 lines of evidence he used to support his theory.
Bellringer #2
Thinking Critically: Oil deposits approximately 200 million years old have been discovered in
Brazil. Where might geologists find oil deposits of a similar age? Explain.
Bellringer #3
1. Magnetic minerals in undisturbed rocks on the ocean floor will do which of the following?
a. Indicate where magnetic pole was at the time of formation
b. Align with “north” as we know it to be now, no matter what
c. Change in their direction of alignment slowly over time
2. How do glacial deposits in Africa, India, Australia, and South America support the idea of
continental drift?
3. THINKING CRITICALLY: Why are the magnetic bands in the eastern Pacific Ocean so far apart
compared to the magnetic bands along the Mid-Atlantic Ridge?
Bellringer #4
1. What do we know about the distribution of earthquakes & volcanoes on Earth?
o They occur randomly across the world
o Quakes tend to happen along plate boundaries but volcanoes are random
o Both quakes & volcanoes tend to occur at plate boundaries
2. If sea floor spreading centers create new crust constantly, does that mean the earth is getting
bigger? Explain.
3. Describe the age of rocks at a mid-ocean ridge.
Bell Ringer # 5
Plate Boundary Review
1. Look at the circled boundary:
A. What type of boundary is it?
B. What are 3 landforms or movements that
are likely to be present?
2. Explain, or draw and label, a convection current.
747142162
-8-
6/18/2017
Bellringer #6 Evidence & Features at Boundaries
Are the following features typical for an oceanic to oceanic convergent boundary?
A = Usually present
1.
2.
3.
4.
5.
B = Not usually present
Volcanoes
Ocean ridge
Folded mountains
Subduction
Rift valley
6. What evidence suggests that Africa & India were once closer to the South Pole?
Bellringer #7
1. How will lithospheric plates that are directly above a rising current move?
 Together or apart?
2. How will a plate above a sinking current move?
 Together or apart?
3. Use ONE word to describe the
A. Lithosphere:
B. Aesthenosphere
4. Which contains the plates? Lithosphere or Aesthenosphere
5. Which has convection currents? Lithosphere or Aesthenosphere
6. Which has oceanic crust? Lithosphere or Aesthenosphere
7. Which is hotter? Lithosphere or Aesthenosphere
Bellringer #8
What type of plate boundary is it IF???
1. Plates are pulling apart
2. Plates are sliding past each other
3. Boundary where you will see mountains
4. Boundary that creates mid ocean ridges
5. San Andreas Fault
6. Mid-Atlantic Ridge
7. Where we see lots of quakes and volcanic activity
747142162
-9-
6/18/2017
Bellringer #9
1. What type of boundary produced the San Andreas Fault?
2. What is a famous example of a divergent boundary?
3. What type of boundary produced the Himalayas? Where are they located?
4. Give a famous example of a subduction boundary. List the continental and oceanic crusts involved.
Bellringer #10
1. Label the tectonic plates
1.
8.
4.
5.
7.
9.
2.
3.
6.
747142162
- 10 -
6/18/2017
Convergent Boundary-3 subtypes
Characteristic
Divergent Boundary
Oceanic to oceanic
Rift valley
Earthquakes
Volcanoes
Island arcs
Mountains-normal
height
Mountains-very high
Subduction zone &
deep sea trench
Example locations
Additional comments
747142162
- 11 -
6/18/2017
Oceanic to
continental
Continental to
continental
Transform
Boundary