Plate Tectonics

  • Created by: Jelena
  • Created on: 14-05-13 21:55

Alfred Wegener's New Theory

  • Alfred Wegener proposed theory of Continental Drift in 1915
  • Proposed that Earth's continents were once joined in a single landmass = Pangaea
  • Pangaea began to break up 200 million years ago --> continents continued to slowly drift
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Proof for this Theory?

  • What proof was there?
  • 1. Similar fossils of plants and animals on different continents
  • 2. Some continents fit together like a jigsaw puzzle
  • 3. Mountains of similar age and structure found on different continents
  • 4. Vast climate changes on different continents --> Coal deposits found in Antarctica --> It must have been close to the equator a long time ago to be temperature and have a swamp
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Wegener's Theory Rejected

  • Theory had 2 big flaws
  • 1. What caused the continents to move?
  • 2. How are the continents moving?
  • He proposed they plowed through the stationary ocean floor
  • Peers argued that crusta rock too brittle to do so w/o fracturing
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Theory of Plate Tectonics

  • Says Earth's crust and rigid upper mantle (together make up the lithosphere) are broken into slabs called PLATES
  • 12 major plates --> several smaller ones
  • Plate move in different directions and at different rates (a few inch a year) on top of the asthenosphere 
  • Asthenosphere = partially molten, plastic-like, flowing layer located below solid part of the Earth's mantle
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What Causes the Plates to Move?

  • Convection currents
  • Earth's internal heat escapes through the circulation of Earth's mantle
  • Process known as convection
  • Hotter material rises and cooler material sinks
  • Convection causes volcanoes, eruptions, earthquakes, and the movement of plates
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Seafloor Spreading

  • New ocean crust is formed at ocean ridges and destroyed at deep-sea trenches
  • Magma, because it is hotter and less dense than surrounding mantle material, is forced toward the crust along an ocean ridge and fills the gap that is created
  • When the magma hardens, a small amount of new ocean floor is added to Earth's surface
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Plate Boundaries

  • 1965
  • Canadian geologist J. Tuzo Wilson first characterized the three basic types of plate boundaries: divergent, convergent, and transform
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