The Puzzling Plates Part I

Transcription

1 The Puzzling Plates Part I Original Source: Dr. Leslie Sautter (Dept. of Geology, College of Charleston) There are two parts to this activity, which is an expanded version of the activity The Puzzling Plates that accompanies the 3-D Plate Tectonics Puzzle, developed by Dr. L. Sautter. Part I does not require the 3-D Puzzle, but allows teachers to construct their own 2-layer version of the puzzle. Grade Level: SC Standards: National Standards: 5 th and 8 th 5 th IIIA2a,b,c 8 th IIIB4a Earth and Space Science Content Standard D Focus Questions What earth layers are included in the different types of lithospheric plates? What are the relationships between lithospheric plates and seafloor features? Objectives Students will: investigate the components of the lithosphere and lithospheric plates. identify the associations among various seafloor features, continental features and the edges of plates. compare different types of plates (oceanic plates, continental plates). compare and contrast the difference between the major ocean basins with respect to the types of plates found in each. Key Words crust upper mantle lithosphere lithospheric plate continental plate oceanic plate Materials For the teacher (to make one puzzle): 2 physiographic maps of the ocean floor (recommended map: by TASA Graphic Arts, Inc., available through Syzygy Arts, Inc.: scissors exact-o knife thin cardboard (preferably corrugated, as it is less likely to warp over time). The amount needed is the same size as the physiographic map being used. Posterboard or card-weight paper (optional). globe For each collaborative group of students: a puzzle consisting of the cardboard and map pieces. Time Frame One to two 50-minute class periods (after puzzles pieces have been cut) Suggested Learning Environment This activity works well with a small (2-3 students) collaborative learning group. Each group will require a set of the puzzle pieces. Relevant pages in Of Sand and Sea Chapter I, The Ocean Planet, pp Teacher Preparation This activity is designed to follow Introduction to the Seafloor and Quakes and Plates, and begins to explain our understanding of how the earth s outer surface is fractured into large pieces of crust and upper mantle, referred to as lithospheric plates. Prior to conducting this activity the puzzle pieces must be constructed. Instructions follow.

2 Constructing the Cardboard Plate Puzzle The cardboard will be cut into the shapes of the tectonic plates to form one layer of the 3-D puzzle: the upper mantle. The physiographic map will also be cut into plate-size pieces and will represent the crust that lies on top of the upper mantle. The two layers are assembled at different stages of the activity. To cut the puzzle, use the following directions: (Time necessary is approximately 1 hour.) a. Lay one physiographic map on top of the uncut piece of cardboard. Tape the edges of the map to the cardboard. Do not affix the map to the cardboard permanently, as the map pieces (crust) must remain separate from the cardboard (upper mantle). b. With Figure 1 as a guide and using the exact-o knife, carefully puncture the map (piercing into the cardboard) along the locations of plate boundaries. Make many perforations so that the plate boundaries will be identifiable on the cardboard. NOTE: At this stage, you will not actually cut the pieces, but the knife will mark the plate boundary locations on the cardboard, so that the map and cardboard can be cut separately. This method will allow the cardboard puzzle layer (the upper mantle) to fit well with the overlying crust (both continental and oceanic crust). c. Remove the perforated map from the cardboard. If you choose to, glue the map to posterboard (or card weight paper). After the glue has dried use scissors (or the exact-o knife to cut along the plate boundary perforations to create the crust portion of the lithospheric plates. d. Cut the cardboard pieces, following the perforations, to create the upper mantle portion of the tectonic plates. Before initiating the activity: e. Separate the puzzle into 2 piles: upper mantle (cardboard pieces) and crust (map pieces). f. Hide the puzzle piece piles and physiographic maps from view. Do not tell students about the puzzle, or that the puzzle relates to the ocean floor map. NOTE: the actual boundary between the North American Plate and the Eurasian Plate (north of the Pacific Ocean) is not well defined and is in debate by scientists. This activity uses the extension of the western end of the Aleutian Islands through Siberia as the boundary. Procedure The steps that follow are included in the STUDENT PAGES. Additional information on the TEACHER PAGES is included in blue italics. 1. On the table is a pile of cardboard puzzle pieces. Work with your team to assemble the puzzle. The edges of the completed puzzle will be straight. 2. Now, think back to the previous activity, Introduction to the Seafloor. How do the shapes of these puzzle pieces relate to the seafloor? a. Identify the puzzle piece that represents the portion of the Pacific Ocean that you traced previously on the ocean floor map. Recall the seafloor features that nearly encircled the Pacific Ocean (what are they?). Hold up the puzzle piece so your teacher knows you are ready to continue. 2

3 3. Your teacher will now provide you with a seafloor map that is the same size as the puzzle. Lay the map next to your puzzle. a. Lay the puzzle piece you selected in number 2 on the appropriate part of the seafloor map. How do you know where to place it? Confer with your team-mates and agree on the location, using the knowledge you gained from the previous activity. 4. Find and place on the map other puzzle pieces that lie completely within the Pacific Ocean and contain no continents. Be sure you do not include the puzzle pieces that would cover the continent of Antarctica. a. How many pieces are found in the Pacific? Describe the seafloor and continental features that surround each of these plates. Students should select the puzzle pieces that represent the following oceanic plates: Philippine, Cocos, Nazca, Juan de Fuca. Each puzzle piece (plate) has at least one trench associated with it, and several have mid-ocean ridges (such as the East Pacific Rise or the Juan de Fuca Ridge). b. The Pacific Ocean should now be almost completely covered with puzzle pieces. Relate the shapes of the pieces to the distribution of earthquake epicenters observed in the Quakes and Plates activity. All the plates are ringed by earthquakes. This is how we first identified the motion and fracturing of the outer Earth. The largest puzzle piece you have placed on the map can now be referred to as the Pacific Plate. (Note: Plate names will all be bulleted and in bold font so you will be able to review them later.) The cardboard piece, however, is only one layer of the plate. It represents the uppermost portion of the earth s mantle, called the upper mantle. Plates that do not include continents are called oceanic plates. The Pacific Plate is the largest oceanic plate on Earth. The other Pacific oceanic plates you have in the puzzle are adjacent to (border) the Pacific Plate: Philippine Plate (to the west) Nazca Plate (to the southeast) Cocos Plate (to the east) Juan de Fuca Plate (the small plate to the northeast) 5. The Pacific Plate 1) is an enormous oceanic plate, 2) nearly covers the entire ocean basin, and 3) lies completely within the ocean basin. Move now to the Atlantic Ocean. Using the three criteria listed above, can you now find an Atlantic Plate? If not, go to number If you had difficulties finding a large oceanic plate that fits entirely within the Atlantic Ocean basin, don t worry. There is no Atlantic Plate! (Sorry, but you needed to discover that for yourself. That s the only trick question, rest assured.) Did you find any plates with no continent included? There are only two small oceanic plates in the Atlantic: Caribbean Plate (south of N. America) Scotia Plate (southeast of S. America) Locate them and place them on the map. 7. Since there is no Atlantic Plate, cover up the Atlantic Ocean with the puzzle pieces (plates) that contribute to its seafloor. Because each of these plates has significant areas covered by continents, we refer to them as continental plates. Again, omit the Antarctic Plate (the reason why will soon be explained). Note: Remember that the earth is a sphere, so puzzle pieces may continue to the other side of the puzzle. 3

4 The Eurasian Plate and Indo-Australian Plates have pieces on both the east and west sides of the puzzle. a. These plates are named for the continents included on them. With your group, be sure to identify each of the following: North American Plate Eurasian Plate African Plate South American Plate. b. What seafloor feature is related to the four major pieces that cover the Atlantic Ocean? The Mid-Atlantic Ridge divides these 4 plates. 8. Move now to the Indian Ocean. Place the puzzle pieces (plates) that comprise the Indian Ocean. Once again, omit Antarctica. One piece includes India, and also stretches eastward to include Australia. This plate has several names and most geologists agree that it is currently breaking apart into two plates. Here we will simply refer to it as the Indo-Australian Plate. 9. The oceans on your map should almost be covered except for the southern portions of the Pacific, Atlantic, and Indian Oceans. Finally, you may add Antarctica to the map! This continental plate is called the Antarctic Plate. This plate was saved until the end because it only appears to be an enormous plate. Because you are looking at a 2-dimensional map view of a 3-dimensional planet, the polar regions are grossly exaggerated. a. Examine the classroom globe to see approximately how large the Antarctic Plate is relative to the Pacific Plate. This plate is mostly continental (not all of the continent is shown on the puzzle) and it is surrounded by a ridge that connects the three oceans. 10. There should be only one small continental piece remaining, the Arabian Plate. Place this piece on the map to complete the puzzle! How many plates do you have? The plates included in this puzzle are only the larger of Earth s plates. There are several minor plates that are too small to illustrate using this model. These 14 plates (or 15 if you break apart the Indo-Australian Plate) are considered to be the major plates of the Earth. Many of these major plates include much smaller micro-plates. 11. On a sheet of paper, make a table (or chart) that lists the four major ocean basins, and the oceanic plates and continental plates that are part of each. If a plate contributes to more than one ocean basin, be sure to include it wherever is necessary. The layer of Earth that you have assembled is the upper mantle portion of the lithosphere. The lithosphere is comprised of the upper mantle and the overlying crust. All of the lithosphere is relatively cold rock, as compared to the deeper mantle and core. So, now you have a map of the earth s upper mantle. The earth s surface layer is still missing the crust. Your teacher will now provide you with the crust layer puzzle pieces. The crust is represented by cut pieces of another copy of the same map you used earlier (which is now under your puzzle!). 12. Place all the crust pieces in their appropriate locations on the puzzle to complete the lithosphere. Each lithospheric plate (another term for plate) is now accurately made of upper mantle (cardboard layer) and crust (top map layer). 4

5 Remember that a plate is comprised of the crust and upper mantle. A plate is a broken piece of the lithosphere. Lithosphere = Crust + Upper Mantle 13. Using your previous observations from steps 2-12, write the name of each plate on a label (or Post-It Note) and affix it to the appropriate plate. If a plate extends to the east-west edges of the puzzle and map, remember to label the plate piece on the other side of the world! 14. Explore the various plates individually by removing them (both crust and mantle) one by one from the puzzle and examining the seafloor features along the plate s edges. a. Make a table (or chart) that lists all of the seafloor features found along the edges of the following five plates: Pacific Plate Nazca Plate South American Plate African Plate Indo-Australian Plate Summarize your observations and discoveries by answering the questions that follow. Questions Use the students completed puzzles and science notebooks to assess the following: Were all plates labeled correctly, including the plates that continue to the other side of the puzzle (Eurasian Plate, Indo-Australian Plate, and Antarctic Plate)? Were tables or charts complete (from Steps 11 and 14)? Examine the student responses to questions 1-7. Key points to look for are shown in blue italics: 1) What are the layers included in the lithosphere? What is a lithospheric plate? Lithosphere is made of the upper mantle and crust. It is a layer of the Earth that breaks into piece called plates, or lithospheric plates. 2) Explain what is meant by the terms oceanic plate and continental plate. An oceanic plate is a lithospheric plate that has little or no continental crust on it. Continental plates have a large amount of continental crust. Most continental plates also have oceanic crust. Only one of the major plates, the Arabian Plate has crust that is nearly all continental crust. 3) In terms of the types of plates found (oceanic plate vs. continental plate), compare the Pacific Ocean basin and the Atlantic Ocean basin. The Pacific Ocean basin is comprised of 5 oceanic plates. Together these plates make up most of the basin. In contrast, the Atlantic Ocean includes only two small oceanic plates. It is dominated by four large continental plates. 4) Is the Indian Ocean basin more like the Pacific Ocean basin or the Atlantic Ocean basin? Justify your answer, using your answer to the previous question. 5

6 The Indian Ocean basin includes three continental plates and, therefore is more like the Atlantic Ocean basin. 5) What is the dominant type of seafloor feature associated with the plates that are included in the Atlantic Ocean basin? What type of plate (oceanic or continental) is found along this seafloor feature? List the four major plates. The Mid-Atlantic Ridge is the major seafloor feature that accounts for the edge of four large continental plates: North American Plate, Eurasian Plate, South American Plate, African Plate. 6) What kind of plate is the Antarctic Plate? What is the dominant seafloor feature that surrounds this plate? The Antarctic Plate is a continental plate that is almost completely surrounded by a mid-ocean ridge. This ridge connects the Pacific, Atlantic, and Indian Ocean basins. 7) What is the dominant type of seafloor feature associated with the northern and western edges of the Pacific Plate? Examine the edges of the adjacent plates - those that touch the Pacific Plate. Is there oceanic crust or continental crust bordering the Pacific Plate? Write a short paragraph, comparing this area with the eastern edge of the Nazca Plate. The western and northern edges of the Pacific Plate are rimmed with trenches. The adjacent plates have oceanic crust at the boundary (even though the Eurasian Plate is a continental plate, at the edge where it meets the Pacific Plate, there is oceanic crust). The Nazca Plate s eastern edge has a trench, but the adjacent plate, the South American Plate has continental crust at the boundary and therefore it is very different from the western Pacific trenches. Students should make this observation. They might also observe how the western Pacific trenches are very arcuate, whereas the southern Peru-Chile Trench is very linear. These are observations made in the first activity, Investigating the Seafloor. In future activities they will see how the trenches are formed. 8) Select one of the 4 plates listed below from the puzzle. Write a story that takes the reader on a tour around the perimeter of the selected plate. Imagine that you are operating a submersible (a manned underwater vehicle with viewing capabilities) just above the seafloor. Describe the features you encounter along the way. Use the World Wide Web and other resources available to find pictures of different seafloor images of mid-ocean ridges, trenches, fracture zones and seamounts to aid with your descriptions. (Nazca Plate, Cocos Plate, Juan de Fuca Plate, Indo-Australian Plate, Caribbean Plate) These plates were chosen because each has a trench, mid-ocean ridge and fracture zones. Seamount are found on each as well, but may not be a dominant feature. Students may be encouraged to present their tour, create a powerpoint presentation, or brochure. Source: Dr. Leslie Sautter, Project Oceanica, Dept. of Geology and Environmental Geosciences, College of Charleston, SC. Contributions to this activity were made by Arla Jessen. website: oceanica@cofc.edu phone: Funding for the COASTeam Program was provided by the South Carolina Sea Grant Consortium. 6

7 Figure 1 Tectonic Plates of the Earth Figure 1. The major lithospheric plates of the earth. The earth is broken into many plates. The boundaries of these plates are well-defined and can be identified by examining the locations of shallow focus earthquakes. Many seafloor features are formed at these plate boundaries, such as trenches and mid-ocean ridges. There are at least 14 major plates on the earth, as well as many smaller plates (micro-plates). Plates are numbered: (1) North American Plate; (2) Philippine Plate; (3) Pacific Plate; (4) Cocos Plate; (5) Nazca Plate; (6) Caribbean Plate; (7) South American Plate; (8) African Plate; (9) Arabian Plate; (10) Eurasian Plate; (11) Antarctic Plate; (12) India-Australian Plate; (13) Scotia Plate; (14) Juan de Fuca Plate. (Figure revised from Of Sand and Sea, by P. Keener-Chavis and L. Sautter, p. 9) 7

8 Figure 2 Cross-section View of the Lithosphere Figure 2. The layers and textures of the lithosphere, both oceanic lithosphere and continental lithosphere, are indicated. (Figure from Of Sand and Sea, by P. Keener-Chavis and L. Sautter, p. 8) 8