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Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first...

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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
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Chapter 17 Plate Tectonics
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Page 1: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

Chapter 17

Plate Tectonics

Page 2: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

Drifting Continents: Early Observations

• Cartographers were the first people to notice matching continents

Antonio Snider-Pelligrini (1858)

Page 3: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

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

Page 4: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

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)

Page 5: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

Fossil Evidence

Page 6: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

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

Page 7: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

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

Page 8: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

Magnetic Patterns and Seafloor Spreading

Page 9: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

Age of Ocean Crust and Seafloor Spreading

Page 10: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

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

Page 11: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

Types of Plate Boundaries: Divergent

• Plates moving apart• Mid-ocean ridge• On land: rift valley

Page 12: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

Types of Plate Boundaries: Convergent

• Continent-continent• Ocean-continent• Ocean-ocean

Page 13: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

Types of Plate Boundaries: Transform

• Plates slide horizontally past each other

Page 14: Chapter 17 Plate Tectonics. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini.

What Causes Plates to Move?


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