After completing this chapter, you should be able to:
- Determine the different layers of the Earth and the distinguishing properties of each layer.
- Understand how seismic waves behave within the different layers of the Earth.
- Understand how seismic tomography has been used to gain a better understanding of the Earth’s interior.
- Understand the Earth’s magnetic field and how it changes over time.
- Learn how to use the program Google Earth for geological applications.
- 2.1: Introduction
- Studying the Earth’s interior poses a significant challenge due to the lack of direct access. Many processes observed at the Earth’s surface are driven by the heat generated within the Earth, however, making an understanding of the interior essential. Volcanism, earthquakes, and many of the Earth’s surface features are a result of processes happening within the Earth.
- 2.2: Interior of the Earth
- The study of seismic waves and how they travel through the Earth has been very useful in helping to determine the changes in density and composition within the Earth and in locating the boundaries between the inner core, outer core, mantle, and crust. Seismic waves are energy waves generated during earthquakes; two types known as P and S waves propagate through the Earth as wavefronts from their place of origin.
- 2.3: Lab Exercise (Part A)
- The following graph (Figure 2.4) displays seismic velocities (in kilometers per second) of P and S waves with depth (measured in kilometers) inside the Earth.
- 2.4: Earth's Magnetic Field
- Overview The thermal and compositional currents moving within the liquid outer core, coupled with the Earth’s rotation, produce electrical currents that are responsible for the Earth’s magnetic field. The shape of the magnetic field is similar to that of a large bar magnet. The ends of the magnet are close to, but not exactly at, the geographic poles on Earth. The north arrow on a compass, therefore, does not point to geographic north but, rather, to the magnetic north.
- 2.5: Lab Exercise (Part B)
- You will use the polar map given to plot the changing locations of the magnetic pole over time. To view the polar map, imagine that you are above the North Pole looking down on it. 90º N latitude is directly in the center of the map, and the lines of latitude, measured in 2-degree increments, spread out in circles from the center. Values of longitude are also given and are represented as lines that radiate out from the center in increments of 30 degrees. A scale bar, in kilometers, is provided.
- 2.6: Google Earth Introduction
- Google Earth is a great tool to visualize and explore many of the geologic features that we will discuss in this class. This first Google Earth assignment will focus on familiarizing you with the program and some of the tools that we will use in later labs. Note that the optimal way to view geology is to go outside. Since that is not an option for an online class, the next best thing is using Google Earth. This is a practical and useful program that has many applications.
- 2.7: Lab Exercise (Part C)
- Answer the following questions using the skills discussed above. In order to prepare you for examining geologic features in Google Earth, let’s first examine a more familiar area, Washington, D.C.
- 2.8: Student Responses
- The following is a summary of the questions in this lab for ease in submitting answers online.
Thumbnail: Earth and atmosphere cutaway illustration. (CCO; Nefronus via wikipedia).