The Way the Earth Works:
Plate Tectonics
Prepared by

Ron Parker,
Earlham College Department of Geosciences
Richmond, Indi...
Plate Tectonics


The paradigm of “How the Earth Works.”
Earth’s outer shell is broken into rigid plates that move.
 Mov...
Plate Tectonics
Tectonic theory evolved in the 1960s.
 Previous research provided a strong foundation.


Wegener (1915) ...
Plate Tectonics
Plate tectonic theory is powerful.
 It provides a unified mechanism explaining:


Igneous, sedimentary, ...
Lithosphere


Tectonic plates are fragments of lithosphere.
Lithosphere is made of both crust and the upper mantle.
 The...
Buoyancy
First described by Archimedes more than 2.2 ka.
 Floating solids displace water equal to their mass.
 An iceber...
2 Types of Lithosphere


Continental ~ 150 km thick.


Granitic crust.
35-40 km thick.
Lighter (less dense) .
More bu...
Plate Boundaries


Lithosphere is fragmented into ~ 20 tectonic plates.



Plates move continuously at a rate of 1 to 15...
Plate Boundaries


Locations on Earth where tectonic plates meet.
Identified by concentrations of earthquakes.
 Associat...
Continental Margins


Where land meets the ocean.
Margins near plate boundaries are “active.”
 Margins far from plate bo...
Plate Boundaries: 3 Types


Divergent – Tectonic plates move apart.

Earth: Portrait of a Planet, 3rd edition, by Stephen...
Plate Boundaries: 3 Types


Convergent – Tectonic plates move together.

Earth: Portrait of a Planet, 3rd edition, by Ste...
Plate Boundaries: 3 Types


Transform – Tectonic plates slide sideways.

Earth: Portrait of a Planet, 3rd edition, by Ste...
Divergent Boundaries
Sea-floor spreading causes plates to move apart.
 Magma wells up to fill the gap.
 Magma cools, add...
Divergent Boundaries


Sea-floor spreading progression.


Early stage
Rifting has progressed to mid-ocean ridge formati...
Divergent Boundaries


Sea-floor spreading progression.


Mid-stage
Ocean begins to widen.
New seafloor is added at th...
Divergent Boundaries


Sea-floor spreading progression.


Late stage
Mature, wide ocean basin.
Linear increase in age ...
Mid-Ocean Ridges
Linear mountain ranges in Earth’s ocean basins.
 Example: The Mid-Atlantic Ridge


Snakes N-S through t...
Mid-Ocean Ridges
Sea-floor spreading opens the axial rift valley.
 Rising asthenosphere melts, forming mafic magma.



...
Mid-Ocean Ridges


“Black smokers” are found at some MORs.
Water entering fractured rock is heated by magma.
 Hot water ...
Ocean Crustal Age


Oceanic crust spreads away from the ridge axis.
New crust is closer to the ridge; older crust farther...
Oceanic Lithosphere
The hot asthenosphere is at the base of the MOR.
 Aging ocean crust moves away from this heat…


 C...
Convergent Boundaries
Lithospheric plates move toward one another.
 One plate dives back into the mantle (subduction).
 ...
Subduction
Old oceanic lithosphere is more dense than mantle.
 A flat-lying oceanic plate won’t subduct.
 Bent down, the...
Convergent Boundaries


The subducting plate descends at an average of 45° .


Plate descent is revealed by Wadati-Benio...
Fate of Subducted Plates?
Plate descent continues past the earthquake limit.
 The lower mantle may be a “plate graveyard....
Subduction Features


Subduction is associated with unique features.
Accretionary prisms.
 Volcanic arcs.
 Back-arc bas...
Convergent Boundaries


Accretionary prisms – Deformed sediment wedges.
Sediments scraped off subducting plates are smear...
Convergent Boundaries


Volcanic arc – Volcanic belt on an overriding plate.
The descending plate partially melts at ~ 15...
Convergent Boundaries


Back arc basin – A marginal sea behind an arc.
Forms between an island arc and a continent.
 Off...
Transform Boundaries


Lithosphere slides past; not created or destroyed.
Many transforms offset spreading ridge segments...
Oceanic Transforms


The MOR axis is offset by transform faults.
Offset of linear MOR is geometric necessity on a sphere....
Transform Boundaries


Oceanic transforms – Offsets along the MOR.


Older interpretation – Faulting occurs after MOR fo...
Transform Boundaries


Continental transforms – Chop continental crust.


Example: The San Andreas Fault.

Earth: Portra...
Triple Junctions
Places where 3 plate boundaries coincide.
 Multiple boundary combinations occur.
 Triple junctions migr...
Hot Spots


Volcanic plumes independent of tectonic plates.
Mafic magmas derived from the lower mantle.
 Tattoo overridi...
Hot Spots
Volcanoes perforate overriding plates.
 Make volcanoes that drift off-plume.


Volcano goes extinct and erodes...
Hot Spots


Hot spot volcanoes create seamounts.
Seamounts age away from originating hot spot.
 Age change marks directi...
Tectonic Boundaries Evolve
Plate boundaries change over geologic time.
 Oceanic plates.


Created at MOR spreading cente...
Continental Rifting


Continental lithosphere can break apart.
Lithosphere stretches and thins.
 Brittle upper crust fau...
Continental Rifting


Example: East Africa.
The Arabian plate is rifting from the African plate.
 Rifting has progressed...
Plate Collision
Subduction consumes ocean basins.
 Ocean closure ends in continental collision.


 Buoyant

continental...
Plate Collision


Plate tectonic collision may involve…
Two continents.
 A continent and an island arc.




Collision ...
Driving Mechanisms


Old: Plates are dragged atop a convecting mantle.
Plate motions are much too complex.
 Convection d...
Driving Mechanisms


Modern: 2 other forces drive plate motions.
Ridge-push – Elevated MOR pushes adjacent lithosphere.
...
Plate Velocities


Absolute plate velocities may be mapped by…
Plotting plate motion relative to a fixed spot in the mant...
Plate Velocities


Plate vectors are determined GPS measurements.
Global Positioning System (GPS) uses satellites.
 Know...
The Dynamic Planet


Plate tectonics: The key to understanding geology.
Mantle is transferred to the surface and back dow...
The Dynamic Planet


Earth’s surface changes continuously.
These changes appear slow to us.
 Geologically, change is rap...
The Dynamic Planet



Plate Tectonics Summary: Ocean floor created at mid-ocean
ridges is consumed at oceanic trenches.

...
The Dynamic Planet



Plate Tectonics Summary: Ocean floor created at mid-ocean
ridges is consumed at oceanic trenches.

...
This concludes the
Chapter 4
The Way the Earth Works: Plate Tectonics

LECTURE OUTLINE

earth

Portrait of a Planet

Third...
Op ch04 lecture_earth3 Subduction
Upcoming SlideShare
Loading in...5
×

Op ch04 lecture_earth3 Subduction

513

Published on

In geology subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge. Regions where this process occurs are known as subduction zones. Rates of subduction are typically centimetres per year, with the average rate of convergence being approximately two to eight centimetres per year

Published in: Education, Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
513
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
57
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Op ch04 lecture_earth3 Subduction

  1. 1. Chapter 4 The Way the Earth Works: Plate Tectonics LECTURE OUTLINE earth Portrait of a Planet Third Edition ©2008 W. W. Norton & Company, Inc. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  2. 2. The Way the Earth Works: Plate Tectonics Prepared by Ron Parker, Earlham College Department of Geosciences Richmond, Indiana
  3. 3. Plate Tectonics  The paradigm of “How the Earth Works.” Earth’s outer shell is broken into rigid plates that move.  Moving plates change the face of planet Earth.   A case study of a scientific revolution.  A powerful idea based on multiple lines of evidence. It allows scientists to predict geologic events, and... Reconstruct the geologic past. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  4. 4. Plate Tectonics Tectonic theory evolved in the 1960s.  Previous research provided a strong foundation.  Wegener (1915) – Evidence supporting continental drift.  Hess / Dietz (1960) – The sea-floor spreading hypothesis.  By 1968, evidence for tectonics was overwhelming.  This evidence changed the view of most geologists.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  5. 5. Plate Tectonics Plate tectonic theory is powerful.  It provides a unified mechanism explaining:  Igneous, sedimentary, and metamorphic rocks.  The distribution of earthquakes and volcanoes.  The origin of continents and ocean basins.  The distribution of fossil plants and animals.  The genesis and destruction of mountain chains.  Continental drift.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  6. 6. Lithosphere  Tectonic plates are fragments of lithosphere. Lithosphere is made of both crust and the upper mantle.  The lithosphere is in motion over the asthenosphere.  Lithosphere bends elastically when loaded.  Asthenosphere flows plastically when loaded.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  7. 7. Buoyancy First described by Archimedes more than 2.2 ka.  Floating solids displace water equal to their mass.  An iceberg “sinks” until the mass of water it displaces is equal to the total mass of the iceberg.  This concept applies to lithospheric plates.  Continental – Floats higher.  Oceanic – Sinks lower.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  8. 8. 2 Types of Lithosphere  Continental ~ 150 km thick.  Granitic crust. 35-40 km thick. Lighter (less dense) . More buoyant – Floats higher.  Oceanic ~ 7 to 100 km thick.  Basaltic crust. 7-10 km thick. Heavier (more dense). Less buoyant – Sinks lower. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  9. 9. Plate Boundaries  Lithosphere is fragmented into ~ 20 tectonic plates.  Plates move continuously at a rate of 1 to 15 cm/yr. This motion appears to be slow on a human time scale.  Yet it is extremely rapid on a geologic time scale.   Plates interact along their boundaries. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  10. 10. Plate Boundaries  Locations on Earth where tectonic plates meet. Identified by concentrations of earthquakes.  Associated with many other dynamic phenomena.   Plate interiors are almost earthquake-free. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  11. 11. Continental Margins  Where land meets the ocean. Margins near plate boundaries are “active.”  Margins far from plate boundaries are “passive.”   Passive margin continental crust thins seaward. Transitions into oceanic crust.  Traps eroded sediment.  Develops into the continental shelf.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  12. 12. Plate Boundaries: 3 Types  Divergent – Tectonic plates move apart. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  13. 13. Plate Boundaries: 3 Types  Convergent – Tectonic plates move together. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  14. 14. Plate Boundaries: 3 Types  Transform – Tectonic plates slide sideways. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  15. 15. Divergent Boundaries Sea-floor spreading causes plates to move apart.  Magma wells up to fill the gap.  Magma cools, adding material to each plate.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  16. 16. Divergent Boundaries  Sea-floor spreading progression.  Early stage Rifting has progressed to mid-ocean ridge formation. Before substantial widening of the ocean. Forms a long, thin ocean basin with young oceanic crust.  Example: The Red Sea Note: This diagram only depicts the crust, not the entire lithosphere. Time 1 Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  17. 17. Divergent Boundaries  Sea-floor spreading progression.  Mid-stage Ocean begins to widen. New seafloor is added at the mid-ocean ridge. Continents move farther apart.  Example: Greenland and the North Atlantic Note: This diagram only depicts the crust, not the entire lithosphere. Time 2 Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  18. 18. Divergent Boundaries  Sea-floor spreading progression.  Late stage Mature, wide ocean basin. Linear increase in age with distance from central ridge. Edge of ocean basin - oldest; ridge proximal - youngest.  Example: The Atlantic Ocean Note: This diagram only depicts the crust, not the entire lithosphere. Time 3 Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  19. 19. Mid-Ocean Ridges Linear mountain ranges in Earth’s ocean basins.  Example: The Mid-Atlantic Ridge  Snakes N-S through the entire Atlantic Ocean.  Elevated ridge (1,500 km wide) 2 km above abyssal plains.  Axial rift valley.  500 m deep. 10 km wide. Symmetric. Site of eruptions. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  20. 20. Mid-Ocean Ridges Sea-floor spreading opens the axial rift valley.  Rising asthenosphere melts, forming mafic magma.   Pooled magma solidifies into oceanic crustal rock.  Pillow basalt – Magma quenched at the sea floor.  Dikes – Preserved magma conduits.  Gabbro – Deeper magma. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  21. 21. Mid-Ocean Ridges  “Black smokers” are found at some MORs. Water entering fractured rock is heated by magma.  Hot water dissolves minerals and cycles back out of rock.  When water reaches the sea, minerals precipitate quickly.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  22. 22. Ocean Crustal Age  Oceanic crust spreads away from the ridge axis. New crust is closer to the ridge; older crust farther away.  Oldest oceanic crust is found at the far edge of the basin.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  23. 23. Oceanic Lithosphere The hot asthenosphere is at the base of the MOR.  Aging ocean crust moves away from this heat…   Cooling, increasing in density, and sinking.  Accumulating increasing thicknesses of sediment. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  24. 24. Convergent Boundaries Lithospheric plates move toward one another.  One plate dives back into the mantle (subduction).  Subduction recycles oceanic lithosphere.  Subduction is balanced by sea-floor spreading.  Earth maintains a constant circumference.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  25. 25. Subduction Old oceanic lithosphere is more dense than mantle.  A flat-lying oceanic plate won’t subduct.  Bent down, the leading edge sinks like an anchor.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  26. 26. Convergent Boundaries  The subducting plate descends at an average of 45° .  Plate descent is revealed by Wadati-Benioff earthquakes. Mark frictional contact and mineral transformations. Earthquakes deepen away from trench.  Quakes cease below 660 km. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  27. 27. Fate of Subducted Plates? Plate descent continues past the earthquake limit.  The lower mantle may be a “plate graveyard.”  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  28. 28. Subduction Features  Subduction is associated with unique features. Accretionary prisms.  Volcanic arcs.  Back-arc basins.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  29. 29. Convergent Boundaries  Accretionary prisms – Deformed sediment wedges. Sediments scraped off subducting plates are smeared and welded onto the overriding plates.  These contorted sediments can be pushed above sea.  Washington’s Olympic Peninsula. Taiwan. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  30. 30. Convergent Boundaries  Volcanic arc – Volcanic belt on an overriding plate. The descending plate partially melts at ~ 150 km depth.  Magmas burn upward, fueling volcanic eruptions.  A curved Earth dictates that volcanic belts are curved.   Arc type depends on overriding plate. Continental crust – Continental arc.  Oceanic – Island arc.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  31. 31. Convergent Boundaries  Back arc basin – A marginal sea behind an arc. Forms between an island arc and a continent.  Offshore subduction traps a piece of oceanic crust, or…  Stretching creates a new spreading ridge.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  32. 32. Transform Boundaries  Lithosphere slides past; not created or destroyed. Many transforms offset spreading ridge segments.  Some transforms cut through continental crust.   Characterized by… Earthquakes.  Absence of volcanism.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  33. 33. Oceanic Transforms  The MOR axis is offset by transform faults. Offset of linear MOR is geometric necessity on a sphere.  Transforms bear strong evidence of sea-floor spreading.  Abundant earthquakes common between ridge segments. Earthquakes vanish past ridge segment overlaps. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  34. 34. Transform Boundaries  Oceanic transforms – Offsets along the MOR.  Older interpretation – Faulting occurs after MOR forms.  Modern interpretation – Faulting occurs with the MOR. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  35. 35. Transform Boundaries  Continental transforms – Chop continental crust.  Example: The San Andreas Fault. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  36. 36. Triple Junctions Places where 3 plate boundaries coincide.  Multiple boundary combinations occur.  Triple junctions migrate and change across time.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  37. 37. Hot Spots  Volcanic plumes independent of tectonic plates. Mafic magmas derived from the lower mantle.  Tattoo overriding plates with volcanoes.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  38. 38. Hot Spots Volcanoes perforate overriding plates.  Make volcanoes that drift off-plume.  Volcano goes extinct and erodes.  Subsidence creates a guyot.  Supports sea-floor spreading.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  39. 39. Hot Spots  Hot spot volcanoes create seamounts. Seamounts age away from originating hot spot.  Age change marks direction of overriding plate motion.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  40. 40. Tectonic Boundaries Evolve Plate boundaries change over geologic time.  Oceanic plates.  Created at MOR spreading centers.  Destroyed at subduction zones.   Continental plates. Torn apart at rifts.  Joined during collision.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  41. 41. Continental Rifting  Continental lithosphere can break apart. Lithosphere stretches and thins.  Brittle upper crust faults.  Ductile lower crust flows.  Asthenosphere melts.  Melts erupt, leading to…   Sea-floor spreading. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  42. 42. Continental Rifting  Example: East Africa. The Arabian plate is rifting from the African plate.  Rifting has progressed to sea-floor spreading in…  The Red Sea The Gulf of Aden  East African Rift – On-going rift. Thinned crust. Elongate trough (channel). Volcanoes. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  43. 43. Plate Collision Subduction consumes ocean basins.  Ocean closure ends in continental collision.   Buoyant continental crust will not subduct.  Subduction ends; mountains are smashed upward. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  44. 44. Plate Collision  Plate tectonic collision may involve… Two continents.  A continent and an island arc.   Collision “sutures” the convergent plate boundary. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  45. 45. Driving Mechanisms  Old: Plates are dragged atop a convecting mantle. Plate motions are much too complex.  Convection does occur.  It is not the prime driving mechanism. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  46. 46. Driving Mechanisms  Modern: 2 other forces drive plate motions. Ridge-push – Elevated MOR pushes adjacent lithosphere.  Slab-pull – Gravity pulls a subducting plate downward.  Convection in the asthenosphere adds or subtracts.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  47. 47. Plate Velocities  Absolute plate velocities may be mapped by… Plotting plate motion relative to a fixed spot in the mantle.  Measuring volcano ages / distance along a hot spot track.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  48. 48. Plate Velocities  Plate vectors are determined GPS measurements. Global Positioning System (GPS) uses satellites.  Knowledge of plate motion is now accurate and precise.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  49. 49. The Dynamic Planet  Plate tectonics: The key to understanding geology. Mantle is transferred to the surface and back down again.  The interior and surface of Earth are in constant motion.  Explains earthquakes, volcanoes, and continental drift.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  50. 50. The Dynamic Planet  Earth’s surface changes continuously. These changes appear slow to us.  Geologically, change is rapid.  Earth looked different in the past.  Earth will look different in the future.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  51. 51. The Dynamic Planet  Plate Tectonics Summary: Ocean floor created at mid-ocean ridges is consumed at oceanic trenches. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  52. 52. The Dynamic Planet  Plate Tectonics Summary: Ocean floor created at mid-ocean ridges is consumed at oceanic trenches. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics
  53. 53. This concludes the Chapter 4 The Way the Earth Works: Plate Tectonics LECTURE OUTLINE earth Portrait of a Planet Third Edition ©2008 W. W. Norton & Company, Inc. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 4: The Way the Earth Works: Plate Tectonics

×