history of the world (the short version) chap 7 intro
TRANSCRIPT
History of the World(the short version)
Chap 7 Intro
Age of Earth
• 4.54 billion years (+/- 1%)
Continental Drift
• Proposed by Alfred Wegener 1915
• Continents formed one landmass in the past—Pangea
• Began breaking apart 200 mill years ago
• Have been moving slowly ever since, now in present position
What evidence did Wegener have?
• Rock Formations– Similar rock types in areas that had been close
together
• Fossils– Similar animal & plant fossils where plates had been
together
• Climate Evidence– Coal deposits in Antarctica– Glacial deposits in Africa, India, Australia & So.
America
or Pangea Ultimata (250 Ma)
When Plates Meet
• Divergent Boundary: plates move apart; cause sea floor spreading at rift valleys. Mid-Atlantic Ridge
• Convergent Boundary (Subduction): one plate slides beneath another; forms small mountains, volcanoes. Mt. St. Helens, Andes
• Collision Boundary: Plates slide together, forced upward. Forms large mountain chains. Alps, Himalayans, Appalachia
• Transform Boundary: faults slide along side one another. San Andreas Fault
• You Try It Plate Tectonics
• Plate Boundary Animation
The untold tragedies of Continental Drift