In chapter 1, the Ring of Fire and plate tectonics were introduced. In this chapter, we further examine how the theory of plate tectonics explains the origins of continents and oceans, folded rocks and mountain ranges, igneous and metamorphic rocks, earthquakes and volcanoes. Just over 100 years ago, the initial concept that went on to become plate tectonics theory was introduced. 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 true revolution in thinking about Earth, which was difficult for many established geologists. Second, there was a political gulf between the main proponent of the theory Alfred Wegener (from Germany) and the geological establishment of the day, which was mostly centred in Britain and the United States. 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.

Learning Outcomes

After studying this chapter, you should be able to

• explain the nebula hypothesis
• understand why parts of the Earth experience seasons
• differentiate between the inner and outer core, mantle, asthenosphere and lithosphere
• understand what generates the Earth’s magnetic field and the function of this field
• identify the key pieces of evidence Wegner used to support his theory
• understand the concept of paleomagnetism
• link Hess and Tuzo Wilson’s to their contributions to the theory of plate tectonics
• identify the three types of plate boundaries and their associated plate movement
• understand the relationship between frequency and magnitude