Continental Drift
Continental Drift Theory Proposed by Alfred Wegener in 1912 250 million years ago, all of the continents were combined into one super-continent called “Pangaea” The continents gradually drifted apart to where they are today.
Plate Tectonics
Earth’s Major Plates Australian-Indian South American Pacific African Eurasian Caribbean Australian-Indian South American Pacific African Juan de Fuca Antarctic North American
Earth’s Major Plates
2 TYPES OF CRUST 2) CONTINENTAL - less dense 1) OCEANIC - very dense - under ocean - thin - very dense 2) CONTINENTAL - less dense
Theory of Plate Tectonics Movement leads to the formation of volcanoes, earthquakes, ocean trenches, mountain formations, etc. Plates move 1-10 cm per year
New Technology Supports Continental Drift Theory Earthquakes and volcanoes occur in concentrated areas. This suggests that the crust is divided into pieces.
In about the late 1940’s, Sonar was invented.
Bats use it!
Sonar brought Wegner’s theory back to life!
Sonar made it possible for us to observe the ocean floor.
Soon, scientists observed a large mountain chain running down the center of the Atlantic ocean.
They quickly found that the ridge ran around the world!
Sea- floor Spreading The longest chain of mountains in the world is the Mid-Ocean Ridge. The mid-ocean ridge extends into all of Earth’s oceans.
Sea- floor Spreading At this ridge, the molten material rises from the mantle and erupts (much like a volcano). Molten material spreads out, pushing older rock to both sides of the ridge.
Sea Floor Spreading- Makes the mid ocean ridge. Animation http://www.wwnorton.com/college/geo/egeo2/content/animations/2_1.htm
Evidence - Drilling Samples The Glomar Challenger did a drilling sample and found rocks that are farther away from the ridge are the older of the rocks. The younger ones were in the center of the ridge.
The further from the Mid Ocean Ridge the rocks are, the older they are; newer rocks in center of ridge
What causes the plates to move? Convection currents in the mantle. Scientists generally agree that convection occurring in the mantle is the basic driving force for plate movement. Utube
Animation
DIVERGENT PLATE BOUNDRY 2 plates move AWAY from each other Forms volcanoes (mid-ocean ridge), cause of seafloor spreading and rift valleys.
DIVERGENT PLATE BOUNDRY 2 plates move AWAY from each other Forms volcanoes (mid-ocean ridge), cause of seafloor spreading and rift valleys. Sea floor spreading Rift valley
If new crust is being added to Earth’s surface, is Earth getting bigger?
CONVERGENT PLATE BOUNDRYS 2 plates move toward each other (COLLIDING) Three things can happen depending on what type of crust is colliding. Oceanic to Continental (Subduction) Continental to Continental (Mountains Form) 3. Oceanic to Oceanic (Subduction)
Continental-Continental Crust on continents have the same density, so they push against each other forming mountains. EX: Himalayan mountain range http://www2.nature.nps.gov/GEOLOGY/usgsnps/pltec/contvscont289x153.gif
Continental/Continental Convergence Found- India (Mt. Everest)
Continental-Ocean More dense crust of ocean is pulled beneath (subducted) the less dense continental crust. Forms trench in ocean Forms volcanoes on land Subduction zone animation http://www2.nature.nps.gov/GEOLOGY/usgsnps/pltec/contvsocn288x157.gif
What is subduction? Subduction is the process by which the ocean floor sinks beneath the continental crust and back into the mantle. Seen in the US on the Pacific Coast.
The Ring of Fire has over 400 volcanoes , both active and dormant. Most of the world’s earthquakes also occur around this ‘Ring of Fire’.
Oceanic/Oceanic Convergence Found- Alaska (Aleutian Islands)
TRANSFORM 2 plates SLIDING HORIZONTALLY past each other Forms earthquakes
Transform – plates sliding horizontally past each other. Found- California (San Andreas Fault) Produces earthquakes!! All plates
Hawaiian Islands How they are formed In action
Tsunami How they are formed Japan 2011