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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