Learning Ocean Science through Ocean Exploration Section 4: Ocean Geologic Features oceanexplorer.noaa.gov Lesson Plan 8 The Biggest Plates on Earth FOCUS the board as a reference during the lesson will be Plate tectonics extremely helpful. You may also give the list as a handout to the students to refer to after the lesson. FOCUS QUESTION How do tectonic plates move, what are some The Background Information has important consequences of this motion, and how do mag- information for use during the initial step of the netic anomalies document the motion at spreading learning procedure when you are explaining centers? concepts of plate tectonics and drift. It may also be helpful to gather several flat rocks to demonstrate LEARNING OBJECTIVES the motion of tectonic plates. It is important to Students will describe the motion of tectonic plates demonstrate how small the movement is annually and differentiate between three typical boundary (several centimeters). types between tectonic plates. MATERIALS Students will infer what type of boundary exists One copy each per student group - Pacific Basin between two tectonic plates, given information on Tectonic Plates and Magnetic Anomalies on the earthquakes and volcanism in the vicinity of the Juan de Fuca Plate boundary. AUDIO/VISUAL MATERIALS Students will infer the direction of motion between Overhead transparency of cross section illustrat- two tectonic plates given information on magnetic ing the main types of plate boundaries (download anomalies surrounding the spreading ridge be- from U.S. Geological Survey web site: http://pubs. tween the plates. usgs.gov/publications/text/Vigil.html) Overhead transparency of map illustrating the Ring ADDITIONAL INFORMATION FOR TEACHERS OF DEAF of Fire (from U.S. Geological Survey web site: STUDENTS http://pubs.usgs.gov/publications/text/fire.html) In addition to the words listed as Key Words, the Overhead projector following word should be part of the vocabulary list: Crust TEACHING TIME Two or three 45-minute class periods The words listed as Key Words are integral to the unit but will be difficult to introduce prior to SEATING ARRANGEMENT the activity. They are really the material of the Groups of two to four students lesson. There are no formal signs in American Sign Language for any of these words and many are KEY WORDS difficult to lipread. Having the vocabulary list on Basalt Ring of Fire 64 64 Learning Ocean Science through Ocean Exploration oceanexplorer.noaa.gov Section 4: Ocean Geologic Features Asthenosphere other locations it is weaker. These variations, called Lithosphere magnetic anomalies, are the result of magnetic Magma minerals in the basalt rocks. If the minerals’ Fault alignment was “locked” into the rocks when the Transform boundary Earth’s magnetic field was similar to its present Convergent boundary magnetic field, then the magnetism of the minerals Divergent boundary is added to the Earth’s magnetic field. Thus the total Subduction magnetic intensity is greater than normal and is Magnetic anomaly called a positive magnetic anomaly. On the other Tectonic plate hand, if the minerals’ alignment occurred when the Spreading center Earth’s magnetic field was opposite to the present, then the magnetism of the minerals is opposite the BACKGROUND INFORMATION Earth’s current magnetic field. The total magnetic This lesson is divided into two parts. First, students intensity is less than normal when measured above will infer whether plate boundaries associated with this negative magnetic anomaly. the Pacific Ring of Fire are divergent, convergent, or transform based on information about When positive and negative magnetic anomalies earthquakes and volcanic activity in the vicinity of are measured on either side of an oceanic spread- the boundaries. In the second part, students will ing center, they form a zebra-striped pattern with use magnetic anomaly data to draw inferences the stripes running parallel to the spreading center about the spreading center system on the divergent ridge. Scientists have reconstructed the history boundary of the Juan de Fuca plate. of magnetic reversals for the past 4 million years using a dating technique based on isotopes of Measurements of magnetic variations on the ocean potassium and argon (see http://oceanexplorer.noaa. floor have provided critical evidence for theories of gov/explorations/02alaska/background/edu/media/mapping7_8. continental drift and plate tectonics. When magma pdf.) They have calculated the age of the magnetic erupts along oceanic spreading ridges, it has high anomaly stripes and the rate at which tectonic mineral content, including magnetic minerals, plates are moving away from the spreading centers. such as iron and magnetite that align with the Earth’s magnetic field like compass needles. As the LEARNING PROCEDURE magma cools to form solid rock (basalt), particles of 1. Review plate tectonics and continental drift. Be magnetite become immobilized, providing a record sure students understand the idea of convergent, of the position of the Earth’s magnetic field when the divergent, and transform boundaries, as well magma was extruded. as the types of earthquakes and volcanic activity associated with each kind of boundary: The Earth’s magnetic field reverses at irregular strong earthquakes and explosive volcanoes at intervals of an average of 400,000 years. The convergent boundaries; slow-flowing volcanoes, alignment of magnetic particles in the crust that weaker earthquakes at divergent boundaries; was formed during periods of reversal is opposite strong earthquakes and rare volcanoes at to that of particles produced when the Earth’s transform boundaries. You may want to use magnetic field is oriented similarly to the present. materials from “This Dynamic Earth” and/or Scientists have found that the intensity of the Earth’s “This Dynamic Planet” (see Resources section), but magnetic field varies around spreading centers. do not give away the answers to the predictive In some locations it is stronger than normal, in exercise on the Pacific Basin Tectonic Plates. 65 Learning Ocean Science through Ocean Exploration Section 4: Ocean Geologic Features oceanexplorer.noaa.gov 2. Distribute copies of the Pacific Basin Tectonic EVALUATION Plates. Using the overhead of the Ring of Fire (see Both worksheets may be used to evaluate students’ materials list) have each group decide what type understanding of the concepts presented. Alter- of boundary exists at the indicated sites, based natively or additionally, students may be asked on the direction of plate movement. Tabulate to define key words, and/or identify the type of each group’s results, and lead a discussion of the boundaries and expected conditions at the junctions reasoning behind their conclusions. If you want to of other tectonic plates. use this exercise for evaluation, collect the work- sheets before discussion. EXTENSIONS Have students visit http://oceanexplorer.noaa.gov to study 3. Explain the origins of magnetic anomalies, and the Ring of Fire Expedition discoveries. draw the students’ attention to the area around the Juan de Fuca plate. Do not give too much RESOURCES detail on the plate; just talk about where it is in http://oceanexplorer.noaa.gov – The Ring of Fire expedition relation to the United States and Canada. Be sure documentaries and discoveries the students realize that the small size of the plate brings convergent and divergent boundaries rela- http://pubs.usgs.gov/publications/text/dynamic.html#anchor1930 tively close together. The fact that subduction at 9449 – On-line version of “This Dynamic Earth,” a the convergent boundary with the North Ameri- thorough publication of the U.S. Geological Sur- can plate caused the Mount St. Helen’s eruption vey on plate tectonics written for a non-technical should spark students’ interest. audience 4. Distribute copies of Magnetic Anomalies on the http://pubs.usgs.gov/pdf/planet.html – “This Dynamic Plan- Juan de Fuca Plate to each student or student et,” map and explanatory text showing Earth’s group. Have each group discuss the handout, physiographic features, plate movements, and and write its conclusions about the location of locations of volcanoes, earthquakes, and impact the spreading site on the ridge on the work- craters sheet. Lead a discussion of the reasoning behind these conclusions. Students should infer that the NATIONAL SCIENCE EDUCATION STANDARDS magnetic anomalies occur on either side of a Content Standard A: Science as Inquiry divergent plate boundary between the Juan de • Abilities necessary to do scientific inquiry Fuca and Pacific plates with the youngest rocks • Understanding about scientific inquiry closest to the spreading center at the boundary of Content Standard B: Physical Science the two plates. How do they account for the inter- • Transfer of energy ruption in the continuity of the anomaly stripes? Content Standard D: Earth and Space Science There is a transverse fault across the ridge. • Structure of the Earth system THE BRIDGE CONNECTION Activity developed by Mel Goodwin, PhD, www.vims.edu/bridge/geology.html The Harmony Project, Charleston, SC THE “ME” CONNECTION Additional information for teachers of deaf students Have students write a first-hand account of a visit to developed by Denise Monte, Teacher of the Deaf a plate boundary, describing where the boundary and Audiologist, American School for the Deaf, occurs and what conditions are found there. West Hartford, Connecticut CONNECTION TO OTHER SUBJECTS English/Language Arts,