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Chapter 12 Section 1 The Evolution of Earth’s Crust.

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1 Chapter 12 Section 1 The Evolution of Earth’s Crust

2 Chapter 12 Section 1 – What You’ll Learn - page 354 Before you read - write the reading’s objectives in this space: 1 – _____________________________________________________________________________________________ 2 – _____________________________________________________________________________________________

3 In 1915, Alfred Wegener (VEG nur) proposed a hypothesis that suggested what? _____________________________ _____________________________ __________________________________________ __________________________________________ __________________________________________ 1

4 What did Wegener discover about the coastlines? 1- _______________________ 2- _______________________________________________ 3- _______________________ ________________________ ________________________ 2

5 Wegener’s hypothesis was not accepted by his contemporaries because ______________________________________ ____________________________________________ 3

6 What did Dr. Harry Hess a captain in the U.S. Navy during WWII, use to make accurate maps of the sea floor? ___________ Hess proposed a hypothesis of _______________, or ________. What is seafloor spreading? ________________________ ________________________ ________________________ ________________________ ________________________ ________________________ 4

7 When scientists obtained core samples of rock from the ocean floor they found it was thin and about _________ years old. As compared to core samples of continental crust, that were much thicker and are _____________ of years old. 5

8 The Theory of Plate Tectonics evolved in the 1960’s This system consists of about a dozen major plates and many minor ones. These plates “float” like rafts on Earth’s mantle. Just like rafts they may have direct collisions or rub side to side. Plate boundaries are shown in the image on the right. 6

9 What are the three types of plate boundaries? Type: _____________ Type: ______________ Type: _______________ Define -____________________________ _________________ _________________ 7

10 Divergent Plate Boundaries At a mid-ocean ridge (MOR), magma rises along a faulted rift valley, spreads, and cools to form new oceanic crust. This spreading apart is what happens at divergent boundaries. A MOR represents divergence that is well-developed. Divergent boundaries exist as rift valleys, where no mature ocean basins exist yet. 8

11 3 types of Convergent Plate Boundaries Ocean-Continent Convergent Plate Boundaries Less dense thick continental crust overrides more dense thin ocean crust. Ocean crust subducts below continental crust creating a trench and dragging "scum" down that melts and explodes back up in explosive volcanoes. Result: trench and volcanic mountain chains Example: Philippine Trench and Sierra Nevada Mountain Range Ocean-Ocean Convergent Plate Boundaries: One plate with oceanic crust at the front collides with another plate with oceanic crust at the front. The colder more dense of the two crusts subducts beneath the other, creating a trench and dragging "scum" down that melts and explodes back up in explosive volcanic islands, creating island arc. Result: trench and volcanic island arcs Example: Aleutian Trench and Aleutian Islands 9

12 3 types of Convergent Plate Boundaries Ctd… Continent-Continent Convergent Plate Boundaries: one plate with continental crust at the front collides with another plate with continental crust at the front. Rather than subducting, both crusts buckle, folding mountains upward. Result: upfolded mountains Example: Himalayas and Appalachian Mts. 10

13 The main result of transform boundaries is horizontal motion of lithosphere. Example: San Andreas Fault No new lithosphere is forming Transform Plate Boundaries Old lithosphere is not being recycled 11 One of the truly amazing and simultaneously terrifying sites is to see an aerial view of Elkhorn Scarp, a visual scar on the landscape of central California that shows the San Andreas Fault's mark on the land. And according to newly discovered “mud pots”, the San Andreas fault may be longer than previously thought.

14 What drives the plates? ___________________ ____________________________________ ____________________________________ ____________________________________ 12

15 Question 1 __________ is the hypothesis that continents have slowly moved to their current locations. A. Continental drift B. Mid-ocean shifting C. Pangaea D. Seafloor spreading ________________________________________ 13

16 Question 2 Who proposed the hypothesis of continental drift? A. Esker B. Gagarin C. Hess D. Wegener ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ 14


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