Transcript Chapter 17 Notes

Chapter 17
Plate Tectonics
Drifting Continents:
Early Observations
• Cartographers were the first people to
notice matching continents
Antonio Snider-Pelligrini (1858)
Alfred Wegener
• German meteorologist/climatologist
• 1912: proposed the idea of continental drift
– Continents started as “Pangea” 200 million
years ago
– Slowly moving apart to present positions
Evidence for Continental Drift
• Matching coastlines
• Matching rock formations/mineral deposits
separated by oceans
• Climate evidence: fossil ferns
Glossopteris) found in Antarctica, South
America, and India
• Matching fossils on widely separated
continents (Cynognathus, Lystrasaurus,
Mesosaurus)
Fossil Evidence
Flaws of Continental Drift
• Did not explain the immense forces
required to move continents long
distances
• No evidence of continents “plowing
through” the ocean crust
• Continental Drift was rejected until the
early 1960s, when these flaws were
resolved
Seafloor Spreading
• Technology advances in the 1940s and
1950s led to more detailed ocean floor
mapping
• Magnetometer: detects changes in
magnetic fields
• Sonar: found mid-ocean ridges and deep
sea trenches
• Interesting patterns in age of rock samples
Magnetic Patterns
and Seafloor Spreading
Age of Ocean Crust
and Seafloor Spreading
Sediment Depth
and Seafloor Spreading
• Evidence for seafloor
spreading corrected a
flaw of Wegener’s
model of continental
drift
• Continents ride along
while ocean crust
moves away from mid
ocean ridges
Types of Plate Boundaries:
Divergent
• Plates moving apart
• Mid-ocean ridge
• On land: rift valley
Types of Plate Boundaries:
Convergent
• Continent-continent
• Ocean-continent
• Ocean-ocean
Types of Plate Boundaries:
Transform
• Plates slide horizontally past each other
What Causes Plates to Move?