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 ModelDescribe: 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).