Constructive Force 1 A Plate Tectonics 1)Alfred Wegener hypothesized that all of the continents were once connected to form one large land mass called Pangaea.

Evidence of Continental drift 2 a)As a student, and scholar he saw the globe as a broken jigsaw puzzle.

Evidence for Continental Drift 3 b)as a scholar, he collected samples of fossils from all over the world. What he found was that a fossil found on one continent could also be found on another continent usually near the shore .

Evidence for Continental Drift 4 c) he discovered deep scratches in rock on the shores of South Africa. He identified these as caused by glaciers. This shows Climate change

More evidence 5 d) Alfred also discovered coal deposits at exactly the same depth and type located near the same latitude but across the ocean from each other.

What Wagoner couldn’t 6 answer What force is large enough to split and move continents apart from each other?

Advances in Technology Allow 7 More Accurate Observations Sonar developed in WWII is used in 1950 to continue mapping the ocean floor. An underwater ridge is discovered that that encompasses the Earth. A new question is asked.

What is this underwater ridge? 8 More observations were needed before a hypothesis could be formed.

Drilling begins 9 Scientists begin to drill into the ocean floor near the ridge to study rock samples to see if they could learn anything about the ocean floors and the ridge that ran through them.

What is learned through 10 drilling and rock samples The ocean floor is made of basalt! The farther away from ridge the older the rock! What does this tell you ? What is this underwater ridge? Hypothesize Model

Three types of heat transfer 11 Which of these three types of heat transfer can cause the plates to move? Explain Radiation Conduction Convection However this can’t be the only force. Can you find other forces that would cause the plates to move?

2) Plate movements 12 a)Translation- When two plates slide past each each-other in opposite directions. 1) The place where these plates meet are called a transform boundary IE. The San Andreas Fault in CA.

b) Converging plates 13 Where the two plates are colliding The boundary where the two plates meet is called a convergent boundary IE. The island of Japan and the country of Iceland

c) Subduction 14 When one plate moves underneath another plate. This happens because one plate is denser and therefore heavier than the other. This is most likely to happen when an oceanic plate collides with a continental plate.

d)Spreading- 15 Spreading is when two plates move apart from each-other 1)divergent boundaries is the point at which the two plates are moving away from each -other.

Africa’s Great Rift Valley (on land) Example of spreading 16 Africa’s Great Rift Valley (on land) Mid-Oceanic Ridge (under the ocean)

Plate movements below 17 create landforms above Diverging plates Continental crust away from continental crust = Rift valley Oceanic crust away from oceanic crust = Mid ocean ridge

Plate movements below 18 create landforms above Converging plates Continental crust into continental crust = Fault block mountains, folded mountains Continental crust into oceanic crust = Coastal and Volcanic mountains, ocean trench,

Plate movements below 19 create landforms above Translating plates Folded hills, riverbed offsets. No new crust is created or destroyed.

Final slide http://lg.eage.org/free/00040/index.htm