3 Continental DriftWegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent.Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.
4 Continental Drift Evidence: Jig-Saw FitContinents fit together like Puzzle piecesFossil Evidencefossils of same age and species were found in connecting bands on different continentsRock Types and StructureSimilar bands of rocks types and mountain belts connectAncient ClimatesPANGAEA!
7 Rejecting the Hypothesis Most scientists rejected Wegener’s ground breaking hypothesis because he could not provide an explanating of how the plates movedA NEW THEORY EMERGES!
8 Seafloor SpreadingIn Wegener’s theory, continents “plowed” through the sea like bull-dozers.Not the case. Continents are actually connected to plates, which moveContinents actually move with lithospheric plates that are pushed by Mid-Ocean ridges
9 Harry Hess Discovered “Mid-Ocean Ridges Spreading centers for tectonic platesNoticed magnetic stripes on the ocean floor which proved that new crust was being created at these ocean ridgesProvided the mechanism for how the plates moved.
12 Plate TectonicsThe theory explaining how the movements of earth’s “TECTONIC PLATES” or “moving plates” create the geologic events like earthquakes, volcanoes and tsunamis.Lithospheric Plates- giant puzzle pieces connecting on the surface of earth.These sit on top of mantle so they can move around
14 Divergent Boundary Plate moving apart Examples: Mid Atlantic Ocean RidgeEast Pacific RisePlates are being pushed apart… as they are pushed apart, magma rises from the mantle and fills the void.Mechanism for plate movement
15 Ocean RidgesOceanic ridges are continuous elevated zones on the floor of all major ocean basins. The rifts at the crest of ridges represent divergent plate boundaries.
16 Rift ValleysTears in the earthAlso caused by Divergent Boundaries
17 Convergent Boundaries Two plates crashing togetherColllidingThree types:Continental to ContinentalOcean to OceanOcean to Continental
18 Continent to Continent collision When two continents collide, you will get mountain rangesExample: Himalayans (India crashing into Asia)
20 Ocean to Ocean Convergance Two oceanic slab converge together. One is pulled under the otherOften forms volcanoes on seafloorVolcanic Island ArcsAleutian IslandsAlaska
21 Ocean to Ocean Convergent Aleutian Island, Alaska, US
22 Ocean to Continental Convergance ALSO KNOWN AS SUBDUCTION ZONEOceanic plate is forced down into the mantle beneath a second continental plateCreates volcanoes and deep ocean trenchesExamples Andes and Marianna TrenchMarianna Trench is deepest place in the WORLD! 35,000 feet deep!!!!!
25 Subduction Zone process Denser ocean slab pulled underneith continentAs it is pulled under, the oceanic crust begins to melt.When crust begins to melt, magma risesMagma rises to surface and creates volcanoes
26 Transform BoundariesPlates grind past each other without destroying or creating new lithosphereLike cars passing each other on a highwayCreates tremendous earthquakesExample: San Andreas Fault
28 How do Plates Move? The crust lies on top of the mantle. It is believed that convection currents cause movement in the asthenosphere. Heat rises from interior.Areas where the asthenosphere is raising causes plates to move apart (diverge) and areas where the asthenosphere is sinking causes plates to move together (converge).
29 Why do plates move? Clear answer is yet unknown There are theories for “Ridge Push”, “Trench Suction”, and just plain old “Gravity”