1. 10.02.d 4 th Piece of Evidence: Magnetic Striping of Sea Floor Blackboard Exercise: Calculate Sea floor spreading rate…

2. Thinnest near mid-ocean ridges Thickest along passive continental margins Thick offshore of large rivers 5 th Piece of Evidence: Sediment Thickness Pattern

3. Age increases systematically out from ridge Mid-ocean ridges less deep because young Deepest seafloor is oldest Age patterns truncated at trenches Depth (dark is deep) Age (orange is young) Correlation of sea floor depth and age

4. 6 th Piece of Evidence: Sea floor heat flow pattern

5. Earth’s Plates / Plate Tectonic Theory

6. Current Plate Tectonic Theory "Chocolate covered cherry" analogy Rigid outer shell Solid core Moveable liquid between the two Earth's Structure 6371 km mean diameter Internal structure characteristics Composition and density Behavior (solid:liquid; weak:strong) Unifying concept of geology Evolution to biology Relativity to physics

7. Current Plate Tectonic Theory Tectonics (Greek tecton = builder) Movement of Lithospheric Plates Large scale geologic processes (landforms, ocean basins, and mountains) Driven by forces deep within the Earth Lithosphere: 12 major plates (boiled egg-shell mode)12 major plates Plate tectonics: processes related to creation, movement, and destruction of plates Plates may include both continents and parts of ocean basins or ocean basins alone; may large (Pacific Plate) or small (Juan de Fuca Plate)

8. How do we know Internal Structure? Primarily based on seismology (earthquakes and seismic waves) – Primary waves (compressional) propagate the fastest (6.5 km/sec in the crust) and pass through liquids and solids. –Secondary (shear) waves propagate through solid materials, but not through liquid; about 4 km/sec in crust –Focus--the site where energy is first released –Focus depth--distance below the surface Link to seismic waves animation: http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm?chapter_no=visualization

9. Internal Structure Inner core (1,300 km dia.) Mostly iron (90%); Some Ni, S, and O Outer core (2,000 km dia.) Liquid similar in composition to inner core Densities of inner and outer cores about same =10.7 g/cm 3 Earth's average density; ~5.5 g/cm 3 Mantle (3000 km dia.) Average density=4.5 g/cm 3 Iron & magnesium silicates The Mohorovicic discontinuity = Between the crust and lithosphere Lithosphere –Made up of the rigid mantle and crust –Cool, strong, outermost layer of Earth; averages about 100 km thick –Thin at mid-oceanic ridges; 120 km under oceans –40-400 km thick under continents Asthenosphere – Hot, slowly flowing layer of relatively weak rock – Low seismic velocity zone

10. Crust –Top of the lithosphere –Less dense than mantle –Oceanic crust »6-7 km thick »More dense than continental crust »Less than 200,000 My years old –Continental crust »May be billions of years old »Different geologic histories »Average thickness about 35 km (70 km max.) Internal Structure Continued

11. Processes Driving Plate Motion –Convection cells to cycle materials on long residence times (500 my) –Powered by heat from outer core and radioactivity.

12. Internal Structure –Epicenter-- surface projection from center through the focus –Seismic waves can be reflected and refracted (Snell's law: n 1 sin  1 =n 2 sin  2 ) –P-waves show low velocity zone at core-mantle boundary; some reflected or refracted –S-waves dissipated at the core- mantle boundary suggesting a liquid outer core

13. Plate Boundaries Divergent (spreading centers)Divergent – Mid-Oceanic ridges – Iceland – African Rift Valley Convergent (subduction)Convergent – Ocean-ocean (Japan and other Pacific trenches) – Ocean-continent (Andes Mts. in Latin America) – Continent-continent (Himalayan Mts. between India –and China) Transform (San Andreas fault)Transform Triple junctions (Mendocino triple junction, Red Sea, and others)Triple junctions Show animation (Atwater) of plate boundary movement/migration

14. Plate Boundaries

15. Fig.4.17b R. E. Wallace (228), U.S. Geological Survey Plate Boundaries in the field

16. Fig.4.21 W. W. Norton Application of Plate Tectonics – Hawaiian Island Chain and Plate Motion History

17. Fig.4.22a W. W. Norton Application of Plate Tectonics – Hawaiian Island Chain and Plate Motion History

18. Fig.4.22b W. W. Norton Origin of Hawaiian Island Chain – Hotspot/Mantle Plume

19. Plate Tectonics and Environmental Geology Effects Distribution of mineral resources Earthquakes and volcanoes Ocean currents and global climate

20. Rock Cycle

22. Hydrologic Cycle

23. Biogeochemical Cycle