Introduction to Week 15

Welcome to week 15! Last week you learned about the theories scientists developed to explain the movement of Earth's tectonic plates. You learned about Wegener's theory of continental drift and Hess's theory of seafloor spreading. You also learned that the theory of plate tectonics emerged as a combination of Wegener's and Hess's ideas.

This week, you will learn about the forces in Earth's interior that cause the lithospheric plates to move around on top of the asthenosphere.