history of the world (the short version) chap 7 intro

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