Each statement represents a primary learning objective for parts of this unit. After you complete the unit, you should be able to:

• Summarize the view that most geologists held prior to the 1960s regarding the geographic positions of the world’s ocean basins and continents.

• List and explain the evidence Wegener presented to support his continental drift hypothesis.

• List the major differences between Earth’s lithosphere and asthenosphere and explain the importance of each in the plate tectonics theory.

• Sketch and describe the movement along a divergent plate boundary that results in the formation of new oceanic lithosphere.

• Compare and contrast the three types of convergent plate boundaries and name a location where each type can be found.

• Describe the relative motion along a transform fault boundary and locate several examples of transform faults on a plate boundary map.

• Explain why plates, such as the African and Antarctic plates, are increasing in size, while the Pacific plate is decreasing in size.

• List and explain the evidence used to support the plate tectonics theory.

• Describe two methods researchers use to measure relative plate motion.

• Describe plate–mantle convection and explain two of the primary driving forces of plate motion.

PLATE TECTONICS IS THE FIRST THEORY to provide a comprehensive view of the processes that produced Earth’s major surface features, including the continents and ocean basins. Within the framework of this model, geologists have found explanations for the basic causes and distribution of earthquakes, volcanoes, and mountain belts. Further, the theory of plate tectonics helps explain the formation and distribution of igneous and metamorphic rocks and their relationship with the rock cycle.