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17.3 & 17.4 Notes Continental Drift Main Points: The theory published by Wegner states that the continents were once all connected and they continually drifted apart.
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Pangaea Explain: A super-continent believed to exist about 200 million yrs ago. Look at a world map & the continents seem to fit together like a jigsaw puzzle.
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Dinosaur Fossils Explain: Fossils from the same dinosaur (Mesosaurus) exist in both S. America & S.W. Africa. Evidence Against Wegner’s Pangaea Theory: Another popular theory said that land bridges formed between continents, explaining how Mesosaurus got back & forth.
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Other Fossil Examples
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http://www.ibtimes.com/full-dinosaur-skeleton-found-alaska- plus-photos-rare-dinosaur-fossils-835539 Full Dinosaur Skeleton Found in Alaska, Plus Photos of Rare Dinosaur Fossils July 2011 Tongass National Forest
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Dino Tracks in Alaska, 2013 Yukon River 9 min video http://www.youtube.com/watch?v=nNGX2LhK5pI
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Glaciers Explain: Evidence of glaciers was found in hot, dry Australia.
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Tropical Plant Fossils Explain: Fossils of tropical plants were found in non-tropical regions
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Arthur Holmes’s Evidence 1944 Describe: Holmes stated that convection within the mantle could move continents.
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Technological Evidence Describe: Scientists found very young rocks on the ocean floor & evidence of the ocean floor spreading & magnetic striping.
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Earths Mechanical Layers Lithosphere Structure: Mostly solid rock Location: Top layer, includes continents & ocean floor. Thickness=few km-250 km under mountains. Describe Movement: Lithosphere is broken into 7 major plates that move atop the asthenosphere.
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Asthenosphere Structure: Deformable rock Location: Found under lithosphere & above mesosphere. Makes up large portion of upper mantle. Average depth = 400-700 km. Describe Movement: Due to convection.
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Mesosphere Structure: Nearly solid because of high pressures Location: Lower mantle Describe Movement: Influences convection in the mantle, so it indirectly leads to movement of the plates.
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Transform Boundaries Describe: Where 2 plates slide past each other & creates earthquakes. Structures Created: Faults (ie.San Andreas fault).
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Divergent Boundaries Describe: The location where 2 plates move apart from each other. Structures Created: Oceanic ridges. Rifts are formed where ridges split apart.
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Convergent Boundaries Describe: Where 2 plates smash into each other.
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Structures Created by Convergent Boundaries Oceanic/Continental Boundaries: Denser oceanic crust goes beneath continental crust & gets destroyed at the “subduction zone”. As oceanic crust melts, it bulges the continental crust & creates volcanic mountains!
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Structures cont. Oceanic/Oceanic Boundaries: When 2 oceanic plates collide; forms volcanic island arcs as the denser, older crust sinks below lighter, younger crust. Each island arc also has a trench.
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Structures cont. Continental/Continental Boundaries: When 2 continental plates collide; forms mountain ranges.
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Convection Currents Model Describe: The mantle moves due to convection, dragging the lithosphere along. Slab-Pull Describe: As plates collide, some crust is subducted & pulls the rest of the crust along with it.
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Slab-Push Describe: A movement caused by the force of magma pushing its way up between 2 plates.
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Hot Plume Describe: Columns of magma rise from lower mantle; causes plate divergence & creates hot spots (long-lived volcanoes).
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