Lesson 8: The Rock Cycle 1/23/15 The Rock Cycle is the process that changes rocks into different types of rocks. Forces such as volcanic activity, weathering, and movement of Earth’s tectonic plates break down old rock and form new. The rock cycle is an ongoing process of forming new rocks from Earth’s existing rock. Discovery Education Video: The Rock Cycle This video explains how rocks change over time and describes the three types of rocks: igneous, sedimentary, and metamorphic. Discovery Education Video: The Rock Cycle Describes how one kind of rock can change from one to another and tells the story of different rocks that they found.