BAESI

1. BAESI Plate Tectonics Ellen Metzger Director, Bay Area Earth Science Institue SJSU Geology and Science Education Program With thanks to Jon Hendricks, SJSU Geology Dept. for slides

2. Overview • Plate tectonics and the Next Generation Science Standards (see handout). • Three components • Science and Engineering Practices • Disciplinary Core Ideas • Crosscutting Concepts • Links to the Common Core standards

3. Plate Tectonics Overview Have the positions of continents moved through time? What is the history of the idea of continental drift? How does plate tectonics work? How do plates interact at their boundaries?

4. Plate Tectonics Slide shows an image of one tectonic plate being subducted beneath another. Plate Tectonics: The scientific theory that the surface of the Earth (lithosphere) is divided into plates that move relative to one another and that interact at their boundaries. Image from USGS

5. Map of the World Slide shows a satellite map of the world. Image from NASA

6. History of Plate Tectonics Slide shows two images made by geographer Antonio Snider-Pellegrini, 1858. One shows the continents separated. The other shows North and South America connected with Europe and Africa. Maps by geographer Antonio Snider-Pellegrini, 1858

7. Glossopteris – “Seed Fern” Slide shows a photo of a Glossopteris fossil, as well as locations on the world map where Glossopteris fossils have been found. Image from USGS Image from NASA Stars show places where Glossopteris fossils have been found.

8. Glossopteris Flora and Land Bridges? Slide shows a photo of a Glossopteris fossil, as well as locations on the world map where Glossopteris fossils have been found. A circle shows the position of the ancient land mass known as “Gondwana”. “Gondwana” Image from USGS Image from NASA Was sea level lower during late Paleozoic?

9. Slide shows a photograph of Alfred Wegener. Alfred Wegener (1880-1930) German meteorologist who proposed idea of “continental drift”:idea that continents moved (and continue to move) horizontally over the surface of the Earth. In 1915 presented evidence for a single supercontinent, which he calledGondwana. Early evidence presented by Wegener and other workers (especially Alexander du Toit) in support of continental drift: Continental fit. Rock sequences. Glacial flow directions. Distributions of fossils. Image from USGS

10. Glacial Flow Directions Slide shows two images. One shows a picture of scratch marks on rocks caused by glacial flow. The second shows ancient glacial flow directions on the modern world map. The third shows that the glacial flow directions in the southern continents only make sense if the continents were once connected. Image from USGS Image from NASA

11. Fossil Evidence Slide shows the distributions of Glossopteris, Lystrosaurus, and Mesosaurus fossils when the southern continents are reunited as Gondwana. Image from USGS

12. Activity:A Plate Tectonic Puzzle

13. History of Plate Tectonics Despite the extensive evidence that the positions of the continents have changed through time, most geologists rejected the idea of continental drift. This was because there was no known mechanism that could produce such change.

14. Interior of the Earth • Inner core: mostly solid iron • Outer core: mostly liquid iron • Mantle: rocky material • Crust: • Oceanic crust • Continental crust • Pressure increases with depth. Slide shows two figures that detail the different parts of the interior of the Earth Images from USGS

15. Earth’s Magnetism • Motion of iron-rich outer core creates a magnetic field. • Earth acts like giant bar magnet with N and S poles. • Geographic and magnetic poles offset. Slide shows a cartoon image of Earth’s magnetic field. Image from USGS

16. Magnetism is Recorded in Rocks Some rocks contain iron minerals. These minerals align themselves to Earth’s magnetic field as the rock forms. Iron particles in sedimentary rock align as they fall out of suspension from water. Iron particles in magma (igneous rocks) align before the magma cools. “Frozen” orientations preserve record of the ancient orientations of Earth’s magnetic field.

17. Study of the Seafloor The seafloor became much better explored during the 1940-1960’s. • WWII, sonar. • Complex topography. • Mid-oceanic ridges with central furrow. • Volcanoes often associated with ridges. Slide shows an artist’s painting of the Mid-Atlantic Ridge. Image from USGS

18. Harry H. Hess & Seafloor Spreading • Hess’ Hypothesis of Seafloor Spreading: • 1962 • Continental and oceanic crust move together. • New oceanic crust forms from rising magma at mid-continental ridges • Oceanic crust moves away from ridge as it cools. • Mechanism: thermal convection. Slide shows a photograph of Harry Hess. Image from USGS

19. Thermal Convection • Thermal convection is thought to be the process driving the movement of plates. • Earth is hotter (due to radioactive decay - fission) in some portions of the deep mantle than in others. • This causes the formation of convection cells that drag along overlying lithospheric plates - acts like conveyor belts. • Think about a container full of boiling water. Slide shows two images. One is a cross-section through the Earth showing how convection cells in the mantle may operate. The other shows a container of boiling water. Images from USGS

20. Testing Hess’ Hypothesis • How could one test Hess’ hypothesis of seafloor spreading? • What pattern should one find on either side of mid-ocean ridge systems if Hess’ hypothesis is true? Slide shows an image of the Mid-Atlantic Ridge. Image from Google Earth

21. Magnetic Reversals • The polarity of Earth’s magnetic field has “flipped” many times throughout the geologic past. • The reason(s) why are not at all clear. • Durations of “normal” and “reversed” polarity highly variable in length.

22. Test of Hess’ Hypothesis • During the early 1960’s, it was discovered that changes in Earth’s magnetic polarity have been recorded into rocks on the seafloor (oceanic crust) as they cooled. • Symmetrical banding on each side of mid-oceanic ridge systems. • Younger rock near ridge, older away. Slide shows two images that illustrate magnetic reversals on either side of a mid-ocean ridge. These reversals form symmetrical patterns on each side of the mid-ocean ridge. Images from USGS

23. Hess’ Hypothesis Was NOT FalsifiedEnough support has since been provided for plate tectonics that the idea is now accepted as a unifying theory for geology.Simple idea with great explanatory power.

24. Ages of the World’s Ocean Basins Slide has one image showing the ages of different oceanic crust rocks in the world’s ocean basins. Image from USGS

25. Activity:A Model of Seafloor Spreading

26. Major Plates of the World Slide shows the major plates of the world. Image from USGS

27. Plates Interact at Their Boundaries Slide shows a figure that details where recent earthquakes have occurred. Most occurred near plate boundaries. Image from USGS; Earthquakes over last 30 days (http://neic.usgs.gov/neis/qed/)

28. Different Plate Boundaries Three major types of plate boundaries: • Divergent - plates diverge from each other. • Convergent - plates converge toward each other. • Oceanic-Continental - oceanic crust (denser) subducts (goes under) beneath continental crust. • Continental-Continental - neither body of continental crust subducts (equal density). • Transform - plates slide past each other.

29. Different Plate Boundaries Slide shows a figure that provides an overview of the three major types of plate boundaries: divergent plate boundaries, convergent plate boundaries, and transform plate boundaries. Image from USGS

30. Divergent Plate Boundary Mid-Atlantic Ridge Slide shows two images. The first shows a picture that illustrates a divergent plate boundary. The second shows the mid-Atlantic ridge system. Image from USGS Image from Google Earth

31. Andes, South America Oceanic-Continental Convergent Plate Boundary Image from USGS Slide shows two images. On is an illustration of a oceanic-continental convergent boundary. The second is an image of the west coast of South America, which is an oceanic-continental convergent boundary. Image from Google Earth

32. Himalaya Mountains, Asia Continental-Continental Convergent Plate Boundary Image from USGS Slide shows three images. One is an illustration of a continental-continental convergent boundary. The second is an image of the Himalayan mountains, which is an example of a continental-continental convergent boundary. The third is a cartoon that shows how India crashed into Asia. Image from USGS Image from Google Earth

33. Transform Plate Boundary Northwestern United States Slide shows two images, both of which illustrate the positions of transform plate boundaries near the northwest coast of the United States. San Andreas Fault Image from USGS Image from Google Earth

34. Activity:Edible Tectonics

35. Activity:Exploring Plate Tectonics with Google Earth

36. Activity:This Dynamic Planet

37. Note:Reconstructions of the arrangements of the continents at various times in the past (and in the future) may be viewed online at http://www.scotese.com/earth.htm