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Experiments

Determining and Measuring Earth's Layered Interior

In this instructional sequence, students examine seismic evidence to determine that the Earth must have a layered internal structure and to estimate the size of Earth's core. Using an inquiry approach, students are divided into two teams (theoreticians and seismologists) to test the simplest hypothesis for what is inside of Earth; the Earth is homogeneous throughout. Theoreticians use a paper and pencil, scale model of a homogeneous Earth combined with an average seismic wave velocity to make predictions about when seismic waves should arrive at various points around Earth (predicted). Meanwhile, seismologists interpret seismic data from a recent earthquake to determine when seismic waves actually arrive at various points around Earth (observations). After comparing and discussing the fit of the predicted data with the observed data, students use a second scale model to further interpret these results. Ultimately, students measure the diameter of Earth's outer core based on their data and can compare it to widely accepted measurements. Before undertaking this activity, students should know what earthquakes are, understand the basics of seismic waves and their prorogation, and be able to explain how seismograms are created.
Objectives:

  • Students will be able to: - Demonstrate that Earth can’t be homogenous by comparing a seismic record section to predicted arrivals from a homogeneous Earth model.
  • Explain how the internal structure of Earth (concentric layers of different density and composition) is inferred through the analysis of seismic data.
  • Explain the role models play in the scientific process, especially when used in combination with observational data.  
  • Explain how models are refined through the collection of additional data
  • Discuss how working in a team to make data-gathering and procedural decisions provides an efficient means for completing tasks, provides peer support to check work and to develop conceptual understanding.

Tutorials:

https://www.iris.edu/hq/inclass/lesson/determining_and_measuring_earths_layered_interior