Earth Systems 3209

1. Earth Systems 3209 Reference: Chapters 4, 15, 16, 19; Appendix A & B Unit: 4The Forces Within Earth

2. Unit 4: Topic 2.3 Plate Tectonic Theory Focus on . . . • describing the theory of plate tectonics.

3. Plate Tectonic Theory • The theory of plate tectonics is one of the great advances in the twentieth century. • In the 1960's, scientist such as Alfred Wegener proposed the “continental drift theory”, and Tuzo Wilson put forth the idea that, “Earth consisted of several different fragments called plates, instead of being made up of one static, rigid, solid layer.” • This revolutionized the way scientist think of Earth today. Text Reference: Pages 525-527

4. Plate Tectonic Theory • A Tectonic Plateis a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. • Plate size varies from a few hundred to thousands of kilometers across, with the Pacific and Antarctic being the largest. • These massive slabs seem to float because of their composition.-- Continental crust is composed of Granitic rocks, which are made of felsic minerals and are less dense. (up to 100km thick)-- Oceanic crust is composed of Basaltic rocks, which are made of mafic minerals and are more dense. (5 – 7 km thick)

5. Plate Tectonic Theory • By the end of the 1960’s the ideas of continental drift and seafloor spreading were united and gave rise to a new theory that better explained the idea of a mobile Earth. This theory was called the Plate Tectonic Theory. • The birth of the plate tectonic theory helped explain various geologic phenomena. Scientist believe that the grinding movements of Earth’s lithospheric plates generate earthquakes, create volcanoes, and deform large masses of rock into mountains.

6. Plate Tectonic Theory • A Canadian geologist named Tuzo Wilson was the person who proposed the Plate Tectonic Theory. • The Theory of Plate Tectonics States: • “Earth’s lithosphere is divided into seven (7) main tectonic plates, namely;1) North American 2) South American3) Pacific 4) African5) Eurasian 6) Australian7) Antarctic • These tectonic plates are in continuous slow motion relative to each other . Motion occurs along one of three types of boundaries bordering each plate.”

7. Ocean Ocean Crust Moho Magma Continental Crust Plate Tectonic Theory • Three Types of Plate Boundaries Include: • Divergent Boundary • Plates move apart, resulting in upwelling of molten material from the mantle to create new ocean floor. • Features on the ocean floor called Ridges, show this form of plate movement. • Tensional forces cause the plates to move apart.

8. Plate Tectonic Theory • Three Types of Plate Boundaries Include: • 2) Convergent Boundary • Plates move together, causing one slab of lithosphere to be consumed into the mantle as it descends beneath the overriding plate. • Features called ocean trenches are formed at these boundaries. Lithosphere isdestroyed at these boundaries. • Compressional forces cause theplates to move together.

9. Birds Eye View or Top View Plate Tectonic Theory • Three Types of Plate Boundaries Include: • 3) Transform Boundary • Plates move past each other in opposite directions. Lithosphere is not created or destroyed at these boundaries. • No vertical movement. For example, San Andreas Fault. • Shearing forces cause the plates to move past one another.

10. Plate Tectonic Theory - Evidence: Earthquakes and Volcanoes Polar Wandering Magnetic Reversals and Seafloor Spreading Ocean Drilling and Heat Flow Hot Spots

11. Example 1: Which Canadian scientist is recognized for his contribution to the Plate Tectonic Theory? (A) Harry Hess (B) Dan McKenzie (C) Drummond Matthews (D) Tuzo Wilson What is the major driving force of plate tectonics? (A) continental drift (B) rifting of the plates (C) plate subduction (D) upper mantle convection

12. Example 2: What happens at a transform plate boundary? major mountain belts are produced by continental collision. new oceanic crust is produced. plates are subducted into the mantle. plates move past each other along a fault. Which plate boundary is demonstrated inthe diagram to the right? compression convergent divergent transform

13. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: According to the plate tectonic theory, Earth is divided into how many major tectonic plates?

14. Solutions . . . Question: Answer:Earth’s surface is divided into sections of lithosphere called tectonic plates. There are seven main tectonic plates which are divided into many smaller tectonic plates.The main tectonic plates include; 1) North American 2) South American3) Pacific 4) African5) Eurasian 6) Australian7) Antarctic

15. Summary . . . Overview of Points covered: • Tuzo Wilson was a major contributor to the plate tectonic theory. • Wilson Stated: • “Earth’s lithosphere is divided into seven (7) main tectonic plates which are in continuous slow motion relative to each other. This motion occurs along one of three types of boundaries bordering each plate.” • Three boundaries are located at the edge of each of the tectonic plates, they include; divergent, convergent, and transform.