Researching the Geology of Africa and South America Your Role: Geologist Geologists comb the landscape describing rock types and large scale structures of the crust. They notice the boundaries between rock types. The call these ‘contacts’ and draw them on maps as lines. They notice and record the thickness and orientation of rock layers. Are they horizontal or tipped over at an angle. They notice if rock layers are bent into folds or ridges. When they are, they measure the direction of an imaginary line along the ridge. Does it point northsouth, east-west or something in-between? Background Information Just as the pattern and color of jigsaw pieces match, the patterns and kinds of rocks along the coasts of Africa and South America should match if the continents were once connected. Geologists have mapped much of South America and Africa to learn about the kinds, ages and folding of the rocks. We cannot expect all the rocks to match because some rocks may have formed after South America and Africa separated. As the split occurred about 200 million years ago, only rocks older than 200 million years should match. The problem is difficult because many of these old rocks lack fossils for determining their ages. Besides comparing the ages of the rocks, the folding of the rocks can be compared. If they are folded to form ridges or mountain ranges, the directions of these ridges or mountains should match. Data about the older rocks at some places are incomplete. Reasons for this are: 1) the older rocks may have been eroded away 2) the older rocks may have been covered by younger rocks or sediments 3) older rocks have been metamorphosed so they cannot be dated chemically 4) no older rocks were deposited, and 5) little information is available because the geologic studies of some areas are too limited. 1 Your Task: 1. You be given an assignment of mapping Africa or South America. You will receive a map of your continent with numbers that represent field locations. You will also receive some field notes that describe each location. 2. Read through the field notes below and present as them as directed on the maps of Africa and South America. To do this, you will have to decide on a key for ages. You could use a color or pattern. (Note: the lines of latitude and longitude are not the boundaries for the colors). 3. Show the trends of the folds, or mountains, with a solid black line. 4. After your map is created meet with another geologist who has mapped the same continent (Africa or South America) as you. Compare your maps. If there are major differences, try to determine why. In the end they should be fairly similar. 5. Now meet another geologist who has mapped the OTHER continent (Africa or South America) as you. 6. Discuss the evidence for continental drift. When fitted together, how well do the ages of rocks match? Do the features, such as contacts and folds align? 7. Does the evidence of the rocks tend to support the idea that the continents may have fitted together? What evidence refutes that conclusion? What are some reasons you can think of for the match not being better? 8. Work together to create a brief presentation on your research. Your presentation should include: A script of key points you will make to the whole group of scientists. You should plan to share the conclusion of your analysis and support it with evidence. A high quality graphic that shows the details of your discovery. You may want to cut and paste your maps onto a small poster. It should have a clear title and a descriptive caption. 2 Field Notes Table 1. Data for South America for Rocks at Points 1 to 16 1. There is a ‘contact’ between two rock types. Draw an east-west line through this point to the coast. Make this line about 1 cm long. North of this line the rocks are older than 2600 million years. South of this line the rocks are about 2000 million years. 2. Rocks are about 2000 million years. 3. Draw a north-south line, about 1 cm long, through this point to the coast. West of this boundary, rocks are 2000 millions years old. To the ease of this line, the rocks are about 600 million years old. 4. 5. and 6. Connect these points with a smooth curved line ending at both ends at the coast to form a small dish-shaped area. To the north of this line (within the dishshaped area) the rocks are 2000 million years old. To the south, the rocks are 600 million years. 7. Rocks here are 600 million years old and they are folded in a northeast-southwest (NE-SW) direction. (Draw a dark line about 1 cm long to show this fold direction.) 8. Rocks are about 600 million years old and they are folded in an east-west direction. (Draw a dark line about 1 cm long to show the fold direction.) 9. Draw an east-west line to show the boundary between 600 million old rocks to the north and 2600 million old rocks to the south near the coast. (Data for this area have been simplified.) 10. Rocks are about 2000 million years old and are folded north-south. 11. 12. 13. and 14. Rocks are mostly 600 million years old and have folds which trend parallel to the coastline. This area is complicated and has some rocks, which are 1000 million years old. 15. Rocks are about 2000 million years old. 16. Rocks are about 2000 million years old and are folded in a northwest-southeast (NW-SE) direction. (Show this with a line 1 cm perpendicular to the coast. 3 Field Notes Table 2. Data for Africa for Rocks at Points 21 to 39 21 & 22. Rocks are about 600 million years old. Draw a solid line between these points to show the direction of folding of these rocks. 23. Draw a boundary line through this point, which trends NNW-SSE. (This is at an angle of about 60 degrees with the longitude line.) Rocks to the west of the line are 600 million years (as at points 21 and 22) but rocks to the ease are older than 2600 million years. 24. Draw a boundary line northeast (NE) from the coast through this point to the intersection of the latitude and longitude lines. Rocks to the northwest are older than 2600 million and rocks to the southeast (SE) are about 2000 million years. 25 & 26. Rocks are about 2000 million years old. 27 & 28. The boundary line connects these two points and extends to the coast. To the west the rocks are about 2000 million years and to the east are about 600 million years old. On the ease side of the line, draw one or two dark lines parallel to the boundary line to show the direction of folds. 29. Rocks are about 600 million years. Data are lacking. 30 & 31. Draw a boundary line connecting these points and extending to the coast. The rocks on the northwest (NW) are about 600 million years and the rocks to the southeast (SE) are older than 2600 million years. On the north side, draw one of two dark lines parallel to the boundary to show the direction of folds. 32. The rocks are about 600 million years old; use latitude line as boundary with older rocks to the north. Draw a line parallel to the coast to show the direction of the folds. 33. Rocks are about 600 million years old. Draw a line parallel to the coast to show the direction of the folds. 34. The rocks here are different; most are 1000 million years old and some are 1300 to 1700 years old. Draw a line to show that they are folded east-northeast to westsouthwest (ENE-WSW). 35. Rocks are about 600 million years old. Draw a northwest-southeast (NW-SE) line to show the direction of the folds. 36. Rocks are about 1000 million years old. Draw an east-west line to show the direction of folds. 4 37. Rocks are about 600 million years old. Draw a northeast-southwest (NE-SW) line to show the direction of folds. 38. Rocks are about 1000 million years old. Draw a northeast-southwest (NE-SW) line to show the direction of folding. 39. Rocks are about 225 million years old, except for a few, which are 2000 million years old at the southern tip of Africa. Draw a dark-east-west line to show the direction of folding. 5 6 7