Ch 10-Plate Tectonics

1. Ch 10-Plate Tectonics • Objectives • Wegener’s hypothesis of continental drift • Process of sea floor spreading • Identify how paleomagnetism provides support for the idea of sea floor spreading • Explain how sea floor spreading provides a mechanism for continental drift • Theory of plate tectonics • Types of plate boundaries • Causes of plate movements • Identify how movements of tectonic plates change Earth’s surface • Summarize how movements of tectonic plates have influenced climates and life on Earth • Describe the supercontinent cycle

2. Continental Drift • Alfred Wegener-German scientist • Hypothesized continents once formed part of single landmass-supercontinent • Broke up into smaller continents 200 million yrs ago during Mesozoic Era • Proposed crumpling of crust produced mt ranges • Concepts in Motion

3. Evidence for Continental drift • Fossil Evidence • Mesosaurus-small extinct reptile found in S America and W Africa • Rock formations • Age and types of rock in W Africa and S America matched closely • Appalachian Mts similar to age and structure to mts in Greenland, Scotland, and N Europe • Climatic Evidence • Ancient glaciers in S Africa and S America • Fossils in tropical swamps covered areas that now have much colder climates • Wegener’s missing mechanism • He believed continents plowed through rock of ocean floor, rejected by scientists • Disproved by geologic evidence and he died in 1930

4. Mid Ocean Ridges • Long, undersea mt chain w/ steep, narrow valley at center • Forms as magma rises from asthenosphere-creates new oceanic lithosphere as tectonic plates move • Rift- crack in ocean floor through which magma rises • Oceanic rocks younger than land rocks

5. Sea Floor Spreading • Process by which new oceanic lithosphere forms as magma rises to Earth’s surface and solidifies at mid ocean ridge • Harry Hess-Geologist suggested ocean floor moving as well as continents in 1950 • Paleomagnetism-study of the magnetic properties of rock • Provided more evidence • http://glencoe.com/sec/science/earthscience/2007/concept_motion/NGS/Visualizing_Seafloor_Spreading_17.swf

6. Paleomagnetism • Magma solidifies to form rock • Iron rich minerals in magma align w/ Earth’s magnetic field, same way compass needle does • Rock hardens, magnetic orientation of minerals becomes permanent • Normal polarity=all rocks w/ magnetic fields that point north, classified in same time period • Reversed polarity=rocks point south • Information supported Hess’s idea of sea floor spreading

7. Sea floor spreading and Continental drift • Scientists reasoned that sea floor spreading provides a way for continents to move other Earth’s surface • Continents are carried by widening sea floor • Wegener redeemed

8. Sec 2-Theory of Plate Tectonics • The theory that explains why and how continents move and is the study of the formation of features in Earth’s crust • Explains how large pieces of lithosphere called plates, move and change shape

9. Crust- thin, solid outermost zone of Earth, 1% of Earth’s mass • Continental and oceanic crust • Mantle-beneath crust, 2,900 km thick, 2/3rd of Earth’s mass • Core-center of Earth, sphere w/ radius of 3500 km, composed mainly of iron and nickel

10. How Continents Move • Lithosphere-solid, outer layer of Earth. Consist of crust and rigid upper part of mantle. Made up of tectonic plates • Asthenosphere-solid, plastic layer of mantle beneath lithosphere. Made up of mantle rock that flows very slowly. Allows tectonic plates to move on top of it • Plastic rock-solid rock that is under great deal of pressure and that flows very slowly • Types of Earth’s Crust • Oceanic-dense and made of rock rich in iron and magnesium • Continental-low density and made of rock rich in silica • Tectonic plates may be made of both • Earths Plates

11. Tectonic Plates • 15 identifiable tectonic plates • Some border major surface features • Some located far from mt ranges • Earthquakes-sudden movements that occur along boundaries of tectonic plates • Frequent earthquakes=2 or more plates meet • Volcanoes-form when plate motions generate magma, erupts on Earth’s surface • Pacific Ring of Fire

13. Types of Plate Boundaries • Divergent-boundary between tectonic plates that are moving away from each other • Magma rises as plates move apart, cools and forms new oceanic lithosphere • Rift valley-narrow valley that forms where plates separate • Most found on oceanic floor • Red Sea • http://www.wwnorton.com/college/geo/egeo/flash/2_11.swf • Convergent boundary-between tectonic plates that are colliding • Oceanic collides w/ continental lithosphere-oceanic subducts which leads to volcanic mts • http://www.wwnorton.com/college/geo/egeo/flash/2_6.swf • 2 continental lithosphere collides-formed Himalayas • 2 oceanic lithospheres collide-forms island arc-chain of volcanic islands-Japan

14. Transform-between tectonic plates that are sliding past each other horizontally, not smoothly • San Andreas Fault • N American plate and Pacific plate • Occurs along mid ocean ridges • Fracture zones-short segments of mid ocean ridge that are connected by transform boundaries

15. Causes of Plate Movement • What is plate motion? Movement of tectonic plates that is a part of the mantle convection system • Convection-movement of heated materials due to differences in density that are caused by differences in temps • Mantle convection • Heated mantle material rises, cooler denser material sinks • Drags overlying tectonic plates along w/ it • http://education.sdsc.edu/optiputer/flash/convection.htm

16. Ridge Push • New rocks at mid ocean ridge cool and slope downward away from ridge • Asthenosphere exerts force on rest of plate=ridge push • Force pushes rest of plate away from mid ocean ridge • Slab Pull • Cooler lithosphere subducts into asthenosphere • Pulls rest of plate, force is called slab pull • Driving force for tectonic plate motion

17. Sec 3-Changing Continents • Cratons-large areas of stable rock that are older than 540 million yrs • Shields-rocks w/in cratons that have been exposed at Earth’s surface • Rifting-process by which Earth’s crust breaks apart • Oceanic or continental • Forms in zone of weakness and continent breaks apart • East African Rift

18. Effect of Continental Change • Continent’s location in relation to equator and poles- affects overall climate • Along w/ oceans and other continents • Air flow, wind patterns, moisture • Continents separate- new species • Madagascar

19. Pangaea • Supercontinent cycle- process by which super continents form and break apart over millions of yrs • Formed 300 million yrs ago • Appalachian and Ural Mts formed when continents collided • Panthalassa was single ocean surrounding • Breakup of Pangaea-200 million yrs ago • Broke up into 2 continents-Laurasia and Gondwanaland • Laurasia broke into N. America and Eurasia • Gondwanaland broke into Africa and S America as one continent and India, Australia, and Antarctica as the other

20. Geography of Future • 150 million yrs from now=Africa colliding w/ Euasia=No Mediterranean Sea • N and S America will move east • No Atlantic Ocean • N and S America will collide w/ Africa • Los Angeles will move north of San Francisco