 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.  Searching for evidence to further develop his theory of continental drift, Wegener came across a paleontological paper suggesting that a land bridge had once connected South America and Africa. This proposed land bridge was an attempt to explain that the same fossilized plants and animals from the same time period were found in South America and Africa.

Continental Drift Animation

 Eurasian  Australian-Indian  Pacific  Juan de Fuca  Caribbean  South American  African  Antarctic  North American

 Explains the movement of Earth’s plates  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 the late 1940’s, Sonar was invented.

Bats use it!

Soon, scientists observed a large mountain chain running down the center of the Atlantic ocean.

 The longest chain of mountains in the world is the Mid-Ocean Ridge.  The mid-ocean ridge extends into all of Earth’s oceans.

 At this ridge, the molten material rises from the asthenosphere and erupts (much like a volcano).  Molten material spreads out, pushing older rock to both sides of the ridge.

Makes the mid ocean ridge.  Sea Floor Spreading with Bill Nye (4 mins)  Divergent Boundary Animation

 The Glomar Challenger took a drilling sample and found that the farther away the rocks were from the ridge, the older they were. The younger ones were in the center of the ridge.

The farther away the rocks are from the Mid- Ocean Ridge, the older the rocks are. The younger rocks are in the center of the ridge.

What causes the plates to move? Convection currents in the asthenosphere. Scientists generally agree that convection occurring in the asthenosphere is the basic driving force for plate movement. Plate Tectonics (7 mins) Plate Tectonics (1 min)

1) OCEANIC  under ocean  thin  very dense  made of basalt 2) CONTINENTAL  under land  thick  less dense  made of granite

Outside of Foldable Convergent Divergent Convergent Transform (slide) (divide) (come together/collide)

 When plates pull apart  Forms volcanoes (mid-ocean ridge), cause of sea floor spreading and rift valleys  Continental-Continental crust diverging causes rift valleys  Oceanic-Oceanic crust diverging causes sea floor spreading

 When plates pull apart  Forms volcanoes (mid-ocean ridge), cause of seafloor spreading and rift valleys Rift Valley Animation Divergent Boundary Animation

Divergent Plate Boundary

 2 plates move toward each other (coming together/colliding)

 Crust on continents have the same density, so they push against each other forming folded mountains.  EX: Himalayan mountain range

CONVERGENT (Continental-Continental) Animation of The Himalayan Mountain Range (1:01 mins)

Convergent Plate Boundary

CONVERGENT (Oceanic-Oceanic) Oceanic-Oceanic convergent zones are mostly hidden under the sea. Only arcs of volcanic islands mark them, made of dark and heavy basaltic lavas. The western Pacific Ocean is full of these—from north to south they include the Aleutian, Kuril, Japanese, Ryukyu, Izu-Bonin, Philippine, Mariana, Solomon and Tonga-Kermadec island arcs. In the Atlantic are the Caribbean and South Sandwich island arcs. In the Indian Ocean is the tangle of arcs that makes up the Indonesian archipelago.

 The more dense oceanic crust is pulled beneath (subducted) the less dense continental crust.  Forms trenches in ocean  Forms volcanoes on land Subduction zone animation

Convergent Plate Boundary

 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). Subduction Zone (1:32 mins)

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’. Ring of Fire Ring of Fire (2:11 mins)

 2 plates SLIDING HORIZONTALLY past each other  Forms earthquakes

San Andreas Fault (3 mins)

Transform Plate Boundary

Animations of processes that occur along plate boundaries. Video on plate boundaries