Where Are We Going?

1. Where Are We Going? Plate Tectonics and the Evidence Behind the Theory

2. Plate Tectonics and the Evidence Behind the Theory As any good scientist would do, we'll begin by asking a few questions: • How did the mountains get there? • What caused the huge tsunami? • What causes some volcanoes to erupt while others lay dormant? These questions arise when we look around us and question what's going on.

3. What Happened Here? For example: Look at these pictures. These pictures were taken near the San Andreas Fault. What made the rocks in the hillsides curve like that?

4. And Here?

5. This is caused by movement of the Earth's tectonic plates. The idea that the Earth has plates of material that are actively moving around and changing the shape of our planet was not articulated until 1912 by Alfred Wegener in what is now known as the Theory of Continental Drift. Continental Drift

6. Wegener believed that these plates were once part of one giant supercontinent, Pangaea, which broke apart and allowed the continents to “drift.” Since then it has been determined that the continents are not just “drifting” but rather moving apart due to plate tectonics. Wegener’s theory was, however, instrumental in paving the way for the Theory of Plate Tectonics. Drifting???

7. Plate Tectonics • The Theory of Plate Tectonics, as proposed by William Ewing and Harry Hess, states that the Earth’s outermost layer is fragmented into a dozen or more large and small plates that are moving relative to one another as they ride above the hotter, more mobile material below. (This Dynamic Earth, USGS, www.usgs.gov)

8. The Earth’s Plates

9. What Evidence Do You Have? In this lesson, we will look at the existing evidence for this theory. The evidence includes: • Fit of the Continents • Fossils • Rocks • Paleoclimatic Patterns • Paleomagnetic Patterns • Sea Floor Topography