Seafloor Spreading: Bathymetry, Anomalies, and Sediments
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Description of the activity/assignment
As far back as 500 years ago, mapmakers drawing the coastlines of South America and Africa noted that the two continents looked as if they might have fit together in the past to form a larger continent. Alfred Wegener incorporated this idea into his hypothesis of continental drift. In spite of the wealth of detail that he assembled, most geologists rejected Wegener's idea of drifting continents, mainly because they found his explanation of exactly how continents could move around the face of the globe to be unconvincing. During the 1940s and 1950s, however, new instruments allowed scientists to map the ocean floors in detail, which finally provided enough evidence to convince the geological community that Alfred Wegener's basic hypothesis of continents in motion was indeed correct.
In Part I, students indentify continental shelves, abyssal plains, and the mid-ocean ridge from a bathymetric map of the South Atlantic Ocean, examine the fits of the coastlines and continental shelves of Africa and South America, and calculate a seafloor spreading rate based on the length of a fracture zone.
Part II involves comparing magnetic anomaly maps from the Reykjanes and Juan de Fuca Ridges, interpreting magnetic profiles across the Mid-Atlantic Ridge and the East Pacific Rise, and calculating rates of seafloor spreading for these two ridges based on paleomagnetism.
In Part III, students compare and contrast maps of bathymetry and sediment thickness and enter data and formulas into Excel to determine the rate of seafloor spreading based on paleontological ages.
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Download teaching materials and tips
- Activity Description/Assignment: Student Instructions for Seafloor Spreading Activity (Microsoft Word 2007 (.docx) 26.4MB Jun15 19)
- Instructors Notes: Lecture Slides for Seafloor Spreading Activity (Acrobat (PDF) 8.6MB Jun15 19)
- Student Handout for Seafloor Spreading Activity (Acrobat (PDF) 32.4MB Jun16 19)
- Student Spreadsheet for Seafloor Spreading Activity (Excel 2007 (.xlsx) 58kB Jun15 19)
Ludman, A., and S. Marshak, 2010, Laboratory Manual for Introductory Geology, Chapter 2, pp. 26-36.
Cook, J., and V. Jones, 2014, Nannofossils Reveal Seafloor Spreading Truth: National Science Teachers Association: Online resource – Accessed 15 June 2019 https://ngss.nsta.org/Resource.aspx?ResourceID=753
Heirtzler, J.R., X. Le Pichon, and J.G. Baron, 1966, Magnetic anomalies over the Reykjanes Ridge: Deep Sea Research, v. 13, pp. 427-433: Online resource – Accessed 15 June 2019 https://www.geological-digressions.com/striped-oceans-and-drifting-continents/
Domeier, M.M., R. Van der Voo, R.N. Tomezzoli, T.H. Torsvik, E. Tohver, B.W.H. Hendrix, H. Vizan, and A.R. Dominguez, 2009, The Pangea Problem: Insights from New Permo-Triassic Paleomagnetic Data from Gondwana: AGU Fall Meeting Abstracts: Online resource – Accessed 15 June 2019 https://www.researchgate.net/publication/253282658
Kious, W.J., and R.I. Tilling, 2016, This Dynamic Earth: the Story of Plate Tectonics: US Geological Survey, ISBN 0-16-048220-8: Online resource – Accessed 15 June 2019 https://pubs.usgs.gov/gip/dynamic/developing.html
Meldahl, K., 2011, Magnetic Reversals and Seafloor Spreading: Online resource – Accessed 15 June 2019 https://www.youtube.com/watch?v=BCzCmldiaWQ
Seafloor Spreading Activity, 2013, National Oceanic and Atmospheric Administration: Online resource – Accessed 15 June 2019 https://oceanexplorer.noaa.gov/edu/learning/2_midocean_ridges/activities/seafloor_spreading.html#none