Name Date Class. continents looked as if they might fit like puzzle pieces into and.

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1 Chapter Outline Plate Tectonics CHAPTER 4 Lesson 1: Continental Drift A. Drifting Continents 1. People looking at early maps noticed that the edges of the American continents looked as if they might fit like puzzle pieces into and. 2. In the early 1900s, Alfred Wegener proposed the hypothesis, which states that the continents move slowly across Earth s surface. 3. He thought that years ago, all of the continents formed one huge landmass he called. 4. The landmass eventually started to, and slowly the continents drifted to their present locations. B. Evidence for Continental Drift 1. Geographic Fit of the Continents a. If the were removed, the continents would fit back together. b. Some and that are now far apart were previously close together. 2. Fossil Evidence a. Wegener studied the fossils of, a seed fern found on continents. b. He didn t believe the heavy seeds could have or 3. Rock Types and Mountain Ranges so far across the oceans. a. Particular groups of on the continents matched. b. match across the continental boundaries. c. The in eastern North America are similar to the mountains in Greenland, Great Britain, and Scandinavia. 36 Plate Tectonics

2 4. Ancient Climate Evidence a. When sedimentary rocks form, they preserve about the climate in which they form. b. Wegener found rocks formed during the time of Pangaea showing that the island of Spitsbergen had a climate. c. Ancient rocks made by were found across Africa, India, and Australia. d. The climates of Pangaea were the climates on Earth today. C. A Hypothesis Rejected 1. Wegener proposed that the drifted by plowing through the seafloor. 2. He thought the same that produced tides had caused the continents to slowly drift over millions of years. 3. Most other scientists did not accept Wegener s hypothesis because they could not think of any strong enough to make continents drift. Lesson 2: Seafloor Spreading A. Investigating the Seafloor 1. was developed for mapping the seafloor using waves. 2. in the middle of the seafloor are called mid-ocean ridges. 3. The closer you move toward a mid-ocean ridge, the the seafloor gets. B. The Seaf loor Moves 1. Harry Hess, an American geologist, suggested a new hypothesis describing how were formed. 2. Seafloor spreading is the process by which new is made at the mid-ocean ridges. Plate Tectonics 37

3 a. Convection brings hot material up from the toward the surface. b. flows out as lava through cracks along the ridge. c. Lava and forms new seafloor. d. The seafloor moves away from the center of the. 3. The age of the seafloor with distance from the mid-ocean ridge. 4. Continents drift as the ocean grows. C. Evidence for Spreading 1. rock records magnetic polarity that occur about every 10,000 years. a. Scientists can measure the magnetic field with an instrument called a. b. By measuring the distance of a stripe of rock from the mid-ocean ridge and determining its age, scientists calculated the of seafloor movement. 4. The seafloor and attached continents move only per year. 5. The boat named the Glomar Challenger and collected samples from the seafloor beginning in Scientists found that the rocks were in the center of the midocean ridge. Lesson 3: Theory of Plate Tectonics A. Earth s Plates 1. Earth s lithosphere is broken into about a dozen large, brittle pieces called. 2. The theory of explains how plates and cause major geologic features and events on Earth s surface. 3. The locations of and indicate the plate boundaries where the lithospheric plates meet. a. The edges of plates run into, move apart, or past each other. 38 Plate Tectonics

4 b. Plates also meet at long, deep parts of the seafloor called. B. Types of Lithosphere 1. Oceanic lithosphere is much than continental lithosphere. a. crust is made up mainly of the dense igneous rocks of basalt and gabbro. b. The oceanic lithosphere is at the mid-ocean ridge and gets as you move farther from the ridge. 2. lithosphere is not as as oceanic crust. C. Plate Movement 1. Convection currents, which transfer energy from inside Earth s mantle to the surface, are thought to drive plate movement. a. Heat the density of rock. b. force pushes the heated rock upward. c. A dense rock plate that sinks back into the mantle is called a. d. Hot rock material is brought near the surface and. e. Rock then cools at the surface, making new at the ridge. f. New rock starts to move away from the. 2. Ridge Push and Slab Pull a. The force of gravity moves the plate downward and away from the ridge during. b. As oceanic crust cools and becomes denser, it is forced into the mantle because of the force of. Plate Tectonics 39

5 D. Measuring Plate Movement 1. The Global Positioning System (GPS) is a network of used to determine locations on Earth and measure the and of plates. 2. Satellite laser ranging (SLR) uses pulses of to measure plate movement. 40 Plate Tectonics