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