17.3 & 17.4 NotesContinental Drift
• Main Points: The theory published by Wegner states that the continents were once all connected and they continually drifted apart.
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.
Dinosaur FossilsExplain: 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.
Other Fossil Examples
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
Dino Tracks in Alaska, 2013
Yukon River
9 min video
http://www.youtube.com/watch?v=nNGX2LhK5pI
Glaciers• Explain: Evidence of glaciers was
found in hot, dry Australia.
Tropical Plant FossilsExplain: Fossils of tropical plants were found in non-tropical regions
Arthur Holmes’s Evidence1944
• Describe: Holmes stated that convection within the mantle could move continents.
Technological Evidence
• Describe: Scientists found very young rocks on the ocean floor & evidence of the ocean floor spreading & magnetic striping.
Earths Mechanical LayersLithosphere
Structure: Mostly solid rockLocation: 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.
AsthenosphereStructure: Deformable rockLocation: Found under lithosphere & above mesosphere. Makes up large portion of upper mantle.Average depth = 400-700 km.
Describe Movement: Due to convection.
MesosphereStructure: Nearly solid because of high pressuresLocation: Lower mantleDescribe Movement: Influences convection in the mantle, so it indirectly leads to movement of the plates.
Transform BoundariesDescribe: Where 2 plates slide past each other& creates earthquakes.
Structures Created: Faults (ie.San Andreas fault).
Divergent BoundariesDescribe: The location where 2 plates move apart from each other.
Structures Created: Oceanic ridges. Rifts are formed where ridges split apart.
Convergent Boundaries
Describe: Where 2 plates smash into each other.
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!
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.
Structures cont.
Continental/Continental Boundaries: When 2 continental plates collide; forms mountain ranges.
Convection Currents Model
Describe: The mantle moves due to convection, dragging the lithosphere along.
Slab-PullDescribe: As plates collide, some crust is subducted & pulls the rest of the crust along with it.
Slab-Push
Describe: A movement caused by the force of magma pushing its way up between 2 plates.
Hot Plume
Describe: Columns of magma rise from lower mantle; causes plate divergence & creates hot spots (long-lived volcanoes).
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