This unit, containing seven lessons, is the first of two units on THE STRUCTURE OF THE EARTH. This collection of activities gives students the opportunity to explore how scientists use earthquake waves to determine the structure of Earth's interior. They will learn to identify the chemical elements that make up Earth's layered structure. They will examine how human-made structures can be reinforced to minimize destruction during an earthquake. Students will investigate how seismologists measure the speed and intensity of seismic waves and learn how to find the epicenter of an earthquake. They will examine the hypothesis that the continents were once joined and how scientists have come to that conclusion using data gathered by seismologists. The UNIT TEST for assessing student performance after completing this unit are included in the next six lessons available in THE STRUCTURE OF THE EARTH (PART B). STUDENT WORKSHEETS and an EDUCATOR GUIDE are included in both downloads.