Plate Tectonic - Plate Tectonics (5) Post Lab
 OBJECTIVES: Making a model of the Earth. Defining plate boundaries. VOCABULARY: crust plate movement plates MATERIALS: Tetrahedron map by NGSDC paste scissors crayons Students trace plate boundaries using earthquake occurrences. Earthquakes are common along the plate boundaries in the Western United States.
 BACKGROUND: The plates are composed of rigid, solid rock. As they move, plates interact at their edges or boundaries. As discussed in the Pre Lab and Lab, there are three basic directions or types of boundary interactions. In some places, two plates move apart from each other; this is called a diverging plate boundary. Elsewhere two plate move together; this is a converging plate boundary. Finally plates can also slide past each other horizontally. This is called a transform plate boundary. Volcanoes and earthquakes help define the boundaries between the plates. Volcanoes form mostly at converging and diverging plate boundaries, where much magma is generated. Earthquakes occur at all three types of boundaries. Because the plates are rigid, they tend to stick together, even though they are constantly moving. When the strength of the rocks at the plate boundary is exceeded, they move rapidly, "catching up" with the rest of the plates. We feel this release of energy as an earthquake. In this exercise, the students will color and assemble a map of the Earth showing earthquakes. The assembled map will make is a tetrahedron (a four-sided geometric figure) of the Earth. This map was designed by John Ward of the National Geophysical and Solar Terrestrial Data Center (NGSDC). The NGSDC acquires, reformats, archives, and distributes worldwide seismological data, many in cooperation with the U.S. Geological Survey. The earthquakes that are plotted on this tetrahedron map were retrieved from the Earthquake Data File for the years 1963-1974 and had magnitudes of 4.5 or greater. PROCEDURE: Before class make a copy of the tetrahedron for each student. Either copy the master sheet onto hard stock paper (50 lb or heavier is ideal, but 20 lb paper will work) or print it from your computer. This will help students make a better model.    Pass out the worksheets. Have the students lightly color the Earth, distinguishing land from the oceans. See if they can define "plates" using the data. Next, instruct them to draw in the plate boundaries. Ask them this question again after they have assembled the tetrahedron. It is much easier to see the plates when the puzzle is put together.    Have the students cut out the tetrahedron and paste it together, gluing the appropriate areas. Make sure that they fold all the black lines before they start to paste, otherwise it is difficult to put the model together.    Discuss the 3 different plate boundaries with the students. Differentiate which boundaries produce earthquakes and/or volcanoes. Converging and diverging boundaries both produce earthquakes. Only earthquakes are common at transform boundaries. Draw pictures on the board to reenforce these points, or use the presentation image below.