Chapter 4. Plate Tectonics

Introduction

Learning Objectives

After carefully reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:

  • Discuss some of the early evidence for continental drift and Alfred Wegener’s role in promoting this theory
  • Explain some of the other models that were used early in the 20th century to understand global geological features
  • Describe the numerous geological advances made in the middle part of the 20th century that provided the basis for understanding the mechanisms of plate tectonics and the evidence that plates have moved and lithosphere is created and destroyed
  • List the seven major plates, their extents, and their direction of motion, and identify the types of boundaries between them
  • Describe the geological processes that take place at divergent and convergent plate boundaries, and explain why transform faults exist
  • Explain how supercontinents form and how they break apart
  • Describe the mechanisms for plate movement

As we discovered in Chapter 1, plate tectonics is the model or theory that we use to understand how our planet works. More specifically it is a model that explains the origins of continents and oceans, folded rocks and mountain ranges, the presence of different kinds of rocks, earthquakes and volcanoes, and changes in the positions of continents over time. So… everything!

Plate tectonics was first proposed just over 100 years ago, but did not become an accepted part of geology until about 50 years ago. It took 50 years for this theory to become accepted for a few reasons. First, it was a radically different perspective on the Earth, and established geologists were reluctant to change their views. The fact that the main proponent, Alfred Wegener, wasn’t trained as a geologist made it easier for them to disregard his ideas.  Second, there was animosity for political reasons.  Alfred Wegener was German, whereas the geological establishment was centred in Britain and the United States- and Britain and the United States were at war with Germany in the first part of the 20th century. Third, the evidence and understanding of Earth that would have supported plate tectonic theory simply didn’t exist until the middle of the 20th century.