Lesson 1 Reading Guide - KC

1. Plate Tectonics • What is the theory of plate tectonics? • What evidence do scientists use to support the theory of plate tectonics? • How do the forces created by plate motion change Earth’s surface? Lesson 1 Reading Guide - KC

2. Plate Tectonics • transform boundary • subduction zone • compression • tension • shear • plate tectonics • continental drift • convergent boundary • divergent boundary Lesson 1 Reading Guide - Vocab

3. Plate Motion • The theory of plate tectonics states that Earth’s crust is broken into rigid plates that move slowly over Earth’s surface. • The rigid plates are called tectonic plates. • North America is part of the North American Plate. Lesson 1-1

4. Plate Motion(cont.) • The movement of one plate is described as either moving away from or toward another plate, or sliding past another plate. • Plates move at speeds of only a few centimeters per year. • At this rate, it takes moving plates millions of years to make new continents, new mountain ranges, or other landforms. Lesson 1-1

5. Plate Motion(cont.) Long before geologists proposed the theory of plate tectonics, they discovered evidence of continental movement. Photo by G.K. Gilbert, U.S. Geological Survey Lesson 1-1

6. Plate Motion(cont.) • In 1912, Alfred Wegener developed the hypothesis that continents move, called continental drift. Lesson 1-1

7. Plate Motion(cont.) • One piece of evidence is the shape of Earth’s continents. • The outlines of South America and Africa match up like pieces of a puzzle. Lesson 1-1

8. Wegener used different types evidence to back up his hypothesis: • Geological evidence • Fossil evidence

9. Plate Motion(cont.) • Fossil and rock evidence from the Gondwana continents also supports the hypothesis of continental drift. Lesson 1-1

10. Geologists have discovered the same types of fossils on continents that are now separated by vast oceans. Lesson 1-1

11. Plate Motion(cont.) • Scientists have also found geological evidence. • Rocks that are made of similar substances and mountains that formed at similar times are present on continents that are now far apart. Lesson 1-1

12. Plate Motion(cont.) • Wegener’s hypothesis of continental drift was not accepted for more than 50 years after it was proposed. • The main reason for this was because he could not explain how the continents could move. Lesson 1-1

13. Plate Motion(cont.) • Convection is the circulation of particles within a material caused by differences in thermal energy and density • Convection affects the mantle underneath tectonic plates. • Hotter mantle rises toward Earth’s surface and cooler mantle sinks deeper into the mantle. Lesson 1-1

14. Plate Motion(cont.) As the Earth’s mantle moves, it pushes and pulls tectonic plates over Earth’s surface. Lesson 1-1

15. Tectonic Plate Boundaries • The edges of tectonic plates are called plate boundaries. • A convergent boundary is where two plates move toward each other. • A divergentboundary is where two plates move apart from each other. • A transformboundary is where plates slide horizontally past each other. Lesson 1-2

16. Convergent Boundaries • When two plates come together, the denser oceanic plate usually is forced down into the mantle and the less dense continental plate remains on Earth’s surface. • The area where one plate slides under another is called a subduction zone. Lesson 1-2

17. Convergent Boundaries • When two continents collide at a plate boundary, both continents remain on the surface. • As two continents push together, the crust rises up and large mountains form. Lesson 1-2

18. Divergent Boundaries • When plates move apart at divergent boundaries, a rift forms between the two plates. • A rift can form within continents when continental crust moves in opposite directions. Lesson 1-2

19. Divergent Boundaries • A rift also can form at divergent boundaries on the ocean floor. • As plates separate, molten rock can erupt from the rift. • As the molten rock cools, it forms new crust. Lesson 1-2

20. Transform Boundaries • Tectonic plates slide past each other at transform boundaries. • The two sides of the boundary move in opposite directions. • This can deform or break features such as fences, railways, or roads that cross the boundary. Lesson 1-2

21. Forces Changing Earth’s Surface • Forces within Earth cause plates to move. • The three types of plate boundaries experience different types of forces. Lesson 1-3

22. The squeezing force at a convergent boundary is calledcompression. • The pulling force at a divergent boundary is called tension. • The side-by-side dragging force at transform boundaries is called shear. Lesson 1-3

23. Forces Changing Earth’s Surface(cont.) • Even though plates move slowly, the forces at plate boundaries are strong enough to form huge mountains and powerful earthquakes. • Tensional forces pull the land apart and form rift valleys and mid-ocean ridges. • Compressional forces form mountains. Lesson 1-3

24. Evidence of continental drift includes fossils, mountain ranges, rock types, and the shapes of continents. • Earth’s crust is broken into pieces called tectonic plates. Convection currents in the mantle cause the plates to move. Lesson 1 - VS

25. There are three types of tectonic plate boundaries. Movement occurs at all three boundaries. Lesson 1 - VS

26. Which boundary is between two plates moving toward each other? A. convergent B. divergent C. subduction D. transform Lesson 1 – LR1

27. Which zone describes the boundary where one plate slides under another plate? A. convergent B. divergent C. subduction D. transform Lesson 1 – LR2

28. Which is the side-by-side dragging force at transform boundaries? A. shear B. tension C. compression D. continental drift Lesson 1 – LR3

29. 1. Continents do not move. 2. Earth’s mantle is liquid. Do you agree or disagree? Lesson 1 - Now