2. The History of Tectonic Theory

3. Presented by Doug Winans Grade Levels 5-8

4. Continental Drift Hypothesis Scientists noted geographic fit of continents 1885 Austrian geologist Edward Seuss notes similarities between plant fossils, and calls the continent "Gondwanaland". 1910 American physicist Taylor proposes concept of continental drift to explain formation of mountain belts. 1912, Wegener names the ancient super-continents "Pangea," based on evidence from geology, climatology and paleontology. Supporting evidence for Continental Drift Hypothesis Geographic fit Geographic fit Fossils Fossils Mountain Belts Mountain Belts Glaciation Glaciation

5. Geographic Fit Continents appear to fit together like pieces of a puzzle

6. Fossils Distribution of fossils found on both sides of the Atlantic Ocean, such as Mesosaurus, and a prehistoric plant called Glossopteris.

7. Mountain Belts Mountain belts, like the Appalachians, match across oceans

8. Glaciation Glacial scoring indicates original location of glaciers and direction of movement Striations are grooves carved in rock by glaciers Blue arrows show direction of glacial flow away from South Pole 

9. Continental Drift Hypothesis Alfred WegenerAlfred Wegener MeteorologistMeteorologist Presented his hypothesis to other professionals, but could not explain how continents driftedPresented his hypothesis to other professionals, but could not explain how continents drifted Try to put together Wegner’s Pangea Pangea

10. Seafloor Spreading

11. Seafloor Spreading Development of a New Theory Continental drift hypothesis was reexamined in 1960’s with new information.Continental drift hypothesis was reexamined in 1960’s with new information. Seafloor SpreadingSeafloor Spreading Evidence supporting seafloor spreading…Evidence supporting seafloor spreading… –Paleomagnetism –Age of Seafloor

12. Seafloor Spreading Harry Hess suggests new seafloor is created at mid-ocean ridges and is destroyed in deep ocean trenches

13. Paleomagnetism Earth’s magnetic field reverses approx. every 600,000 yearsEarth’s magnetic field reverses approx. every 600,000 years As new crust is formed, normal and reverse polarities are preserved in the rock recordAs new crust is formed, normal and reverse polarities are preserved in the rock record 1963, Vine & Matthews observe magnetic anomalies in oceanic crust1963, Vine & Matthews observe magnetic anomalies in oceanic crust

14. Younger rocks (red) are found near mid-ocean ridgesYounger rocks (red) are found near mid-ocean ridges Further away, the age of seafloor gets progressively older (blue)Further away, the age of seafloor gets progressively older (blue)

15. Mechanism for Seafloor Spreading Convection CurrentsConvection Currents –As heated magma rises, it moves away at spreading centers pulling plates apart –Plates slide over the asthenosphere –The upper mantle then cools and becomes more dense – sinking at ocean trenches

16. Plate Tectonics Theory John Tuzo Wilson combined the ideas of Continental Drift and Seafloor Spreading into a new theory… “Plate Tectonics”

17. Tectonic Quiz What evidence was given for the Continental Drift Hypothesis?What evidence was given for the Continental Drift Hypothesis? Glaciation Fossils Geographic Fit All of the Above All of the Above

18. Tectonic Quiz Who proposed the Continental Drift Hypothesis?Who proposed the Continental Drift Hypothesis? Taylor Hess Wegner Seuss

19. Tectonic Quiz New evidence of “Seafloor spreading” was used to develop Tectonic Theory. What evidence did scientists find?New evidence of “Seafloor spreading” was used to develop Tectonic Theory. What evidence did scientists find? Ancient magnetic reversals in the rocks Ocean floor dating GPS measurements Both A and B above

20. Tectonic Quiz Who combined Continental Drift and Seafloor Spreading to produce Tectonic Theory?Who combined Continental Drift and Seafloor Spreading to produce Tectonic Theory? Taylor Hess “Tuzo” Wilson Seuss

21. Plate Tectonics History References Web Sites: Pangaea: The Continent http://www.pangaea.org/wegener.htm http://www.pangaea.org/wegener.htmhttp://www.pangaea.org/wegener.htm What on Earth is Plate Tectonics? http://wrgis.wr.usgs.gov/docs/parks/pltec/index.html Geology Labs: Virtual Earthquake http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html Understanding Quakes http://whyfiles.org/094quake/index.php?g=6.txt ALFRED WEGENER vs JUST ABOUT EVERYBODY ELSE: HOW THE CONTINENTS FORMED http://courses.science.fau.edu/~rjordan/phy1931/WEGENER/wegener.htm This Dynamic Earth: The Story of Plate Tectonics http://pubs.usgs.gov/gip/dynamic/dynamic.html Testing the Sea-Floor Spreading Hypothesis http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part9.html