 In 1915 Alfred Wegener proposed the Theory of Continental Drift  = continents are not fixed and in the past all continents had been joined

The “Supercontinent”

Better maps showed outline of continents fit together like a puzzle  EX: South America & Africa

Identical fossils were found on different continents EX: Mesosaurus

Similar rocks & mountains were found on different continents EX: Appalachian Mts.

 Climate change  Wegener was a meteorologist and studied climate  He found out that there were glacier deposits that showed that between million years ago ICE once covered the southern hemisphere

 How can you move a continent? (what mechanism did this)  Answer: In 1968 the ocean floor was being extensively mapped & earthquakes were being discovered on the ocean floor = gave scientists a “mechanism”

9.2 & 9.3  PLATE TECTONICS  & Actions at Plate Boundaries

 Earth is divided into 8 major lithospheric plates that move and interact on the Earth’s surface because of unequal heating within Earth’s interior

 hot molten material from outer core slowly rises upward, cooler material descends to take its place = circular pattern of magma

 rigid lithosphere slides on top of molten asthenosphere depending on convection currents

 - Interaction of plates causes earthquakes, mountains, and volcanoes

 Divergent = 2 plates are moving apart, allowing magma to upwell, and form new crust EX: SA & African plates - at the boundary an oceanic ridge (mts on the ocean floor) forms on either side of boundary

- exactly at center of boundary is a rift valley where magma reaches surface - can happen on continents too EX: East African Rift

2. Transform = 2 plates are sliding past each other - many found on ocean floor but some on land = Faults EX: San Andreas Fault

3. Convergent = 2 plates are moving closer together (colliding), very complicated because of oceans vs continents

A. Ocean-Continent Collision = heavier ocean crust is forced below continent creating a Subduction Zone - as ocean crust goes deeper, it melts, new magma rises to create volcanoes on continent EX: Andes Mts of SA - subducting ocean creates deep trenches at plate boundary

B. Ocean-Ocean Collision = one slightly heavier slab of ocean crust is subducted beneath the other one - creates volcanic chains in ocean = Volcanic Island Arc EX: Pacific Plate and Eurasian Plate forming the Japanese Islands

C. Continent-Continent Collision = no subduction, continents collide and fold together to create tall & complex mountains EX: Indian Plate colliding with Eurasian Plate forming ….. The Himalayan Mountains

 1. Continental Drift = continents fit together, fossils, rocks, climates 2. Maps of the sea floor showed that close to plate boundaries there was young crust and the farther away from the boundary, the older the crust - ages matched up on either side of the plate boundary  Theory of Sea-Floor Spreading

3. When magma cools it records the direction of North (like a compass), scientists found that N & S pole flip periodically - The sea floor rocks record this flip of poles and match up on either side of the plate boundary  Paleomagnetism

 4. Earthquakes are much more frequent at plate boundaries than anywhere else  WHY??? Plates are moving

5. Ocean drilling showed that ages of sea-floor rock changed, youngest near plate boundary, oldest near the continent coasts - Oceans are much younger than continents (180 million years compared to 4 billion years)

6. Ocean mapping around Hawaii showed it was part of a large chain of volcanoes extending throughout the Pacific The Big Island (Hawaii) is the only one erupting, farther away from this is progressively older

  BUT in the middle of Pacific Plate ???  There is a large plume (ball) of molten magma near surface, melting the crust, and forming a volcano = Hot Spot 

 Pacific plate is moving over the hot spot and creating a chain of volcanoes = indicates direction of movement 