Plate Tectonics

1. Plate Tectonics Mr. Litaker Chapter 9

2. Continents in Motion • Alfred Wegener was a German meteorologist that proposed the theory (1912) that the Earth was not fixed - it "moved" on plates. Come to find, in the 1960s, Alfred Wegner´s theory was proven correct. This theory is known as Continental Drift.

3. Book written by Wegener • In 1915, Wegener published his evidence and conclusions in a now classic book, Die entstehung der kontinente und ozeane (The origin of continents and oceans). Wegener proposed that all modern continents were once assembled together in a supercontinent he named Pangaea.

4. Continental Drift • Theory that the continents had once been part of one or more landmasses that had separated and moved apart. • They are supposed to have broken up about 200 million years ago.

5. http://www.ucmp.berkeley.edu/geology/tectonics.html http://www.ucmp.berkeley.edu/geology/anim1.html

6. Pangaea – Means “ All Earth” • Wegener proposed that all continents had once been joined in a supercontinent he named Pangaea. Pangaea, he thought, had existed from the primordial earth until the Mesozoic, when it began to break up. Wegener at first considered mantle convection as a possible driving mechanism, but later rejected that in favor of Tidal forces as the cause for Pangaea's breakup and continental drift.

8. Enchanted Learning site http://search.netscape.com/ns/boomframe.jsp?query=the+origin+of+continents&page=1&offset=0&result_url=redir%3Fsrc%3Dwebsearch%26requestId%3Dc5358d4649b76afb%26clickedItemRank%3D10%26userQuery%3Dthe%2Borigin%2Bof%2Bcontinents%26clickedItemURN%3Dhttp%253A%252F%252Fwww.enchantedlearning.com%252Fsubjects%252Fastronomy%252Fplanets%252Fearth%252FContinents.shtml%26invocationType%3D-%26fromPage%3DNSCPResults%26amp%3BampTest%3D1&remove_url=http%3A%2F%2Fwww.enchantedlearning.com%2Fsubjects%2Fastronomy%2Fplanets%2Fearth%2FContinents.shtml

9. Panthalassa – Means “All Seas” • 245 Million years ago:  Pangaea existed when some of the earliest dinosaurs were roaming around this big earth. The land Pangaea was surrounded by a sea called Panthalassa.

11. Pangaea breaks up Forming: • Pangaea started to break up into two smaller supercontinents, called Laurasia and Gondwanaland, during the Jurassic period. By the end of the Cretaceous period, the continents were separating into land masses that look like our modern-day continents.

12. 3 continents associated with Laurasia  4 continents associated with Gondwana 

13. Evidence Supporting Continental Drift 1. Continental Margins – Giant Jigsaw Puzzle. These two widely separated continents seem to resemble two separate pieces of a larger jigsaw puzzle. North America, too, seems to mirror the western coastline of Europe.

14. Evidence Supporting Continental Drift • 2. Fossils of Mesosaurus – A small reptile that lived 270 million years ago that was found in Eastern South America and western Africa. Mesosaurus lived near swamps and rivers and it would have been impossible for this reptile to have swam across the Atlantic.

15. Evidence of Continental Drift 3. Glossopteris Fern Fossils Fern fossils have been found in Africa, Australia, India, and Antarctica.

16. Evidence of Continental Drift 4. Glacial Deposits Evidence of Glacial Deposits was found on 5 different continents. Glacial striations on rocks show that glaciers moved from Africa toward the Atlantic Ocean and from the Atlantic Ocean onto South America. Such glaciation is most likely if the Atlantic Ocean were missing and the continents joined.

18. Evidence of Continental Drift 5. Geologic Evidence The age and type of rocks in the coastal regions of widely separated areas, western Africa & eastern Brazil, matched closely. Mountain chains such as the Appalachians and Scandanavian Mtns. Of Greenland and Northern Eupope seem to fit closely in age and structure.

20. Wegener’s Theories Rejected • Most scientist rejected Wegener’s theories --------- Why ? ---------- • It was difficult to conceive of large continents plowing through the sea floor to move to new locations. What kind of forces could be strong enough to move such large masses of solid rock over such great distances? • While in Wegener’s lifetime, he never found the WHY to why the continents moved.

22. Wegener suggested that the continents simply plowed through the ocean floor, but Harold Jeffreys, a noted English geophysicist, argued correctly that it was physically impossible for a large mass of solid rock to plow through the ocean floor without breaking up. Recent evidence from ocean floor exploration and other studies has rekindled interest in Wegener's theory, and lead to the development of the theory of plate tectonics.

23. The WHY is Answered • The WHY came in 1967, when a group of scientist set out to map the ocean floor along the Mid-Atlantic Ridge. This was an undersea mountain chain with a steep, narrow valley running down its center. (65,000 km or 40,625 miles long) • Glomar Challanger – Sent out to collect rock samples at the bottom of the sea for age dating. Results – Seafloor = 70 to 150 m.y.a. and Continent = 3 to 4 Billion.

25. Total distance penetrated below sea floor 325,548 mTotal interval cored 170,043 m Total core recovered and stored 97,056 m Overall core recovery 57%Number of cores recovered 19,119Number of sites investigated 624Deepest penetration beneath ocean floor 1,741 m Maximum penetration into basaltic earth crust 1,080 m Deepest water (Leg 60 Site 461A) 7,044 m Total distance traveled 375,632 nautical mi

26. Intro to Plate Tectonic Theory • Plate tectonics is the theory that Earth's outer layer is made up of plates, which have moved throughout Earth's history. • The theory explains the how and why behind mountains, volcanoes, and earthquakes, as well as how, long ago, similar animals could have lived at the same time on what are now widely separated continents.

27. Definite Proof • But the purpose of the Glomar Challenger was scientific exploration. One of the most important discoveries was made during Leg 3. The crew drilled 17 holes at 10 different sites along a oceanic ridge between South America and Africa. The core samples retrieved provided definitive proof for continental drift and seafloor renewal at rift zones. This confirmation of Alfred Wegener's theory of continental drift strengthened the proposal of a single, ancient land mass, which is called Pangaea.

28. Navy submarine commander during World War II. Harry Hess • Suggested that there was actually a break at the center of the ridge known as a RIFT ZONE. • Magma from deep within the Earth was coming to the surface at this Rift Zone and creating new sea floor. Hess proposes sea-floor spreading1960

29. Earth’s Layers • Earth: built by distinct layers: inner core, outer core, mantle, crust; the crust is the thinnest layer

30. Lithosphere • The rigid blocks of the crust and upper mantle that extend downwards to about 100 km deep.

31. Asthenosphere • Below 100 km a plastic like zone of molten magma extends down to about 200 km thick called the – Asthenosphere. • The less denseLithosphere floats on the more denseAsthenosphere.

33. END

34. Types of Boundaries Divergent Convergent Transform

35. D i v e r g e n t Boundary • A divergent boundary occurs where 2 plates are pulling apart. • The force associated with this is called – Tension. • Example – Mid-Ocean ridges where Sea Floor spreading is occuring.

36. http://www.uwsp.edu/gEo/faculty/ritter/geog101/textbook/earth_materials_structure/ridge_divergence_video.htmlhttp://www.uwsp.edu/gEo/faculty/ritter/geog101/textbook/earth_materials_structure/ridge_divergence_video.html

37. Convergent Boundary: 3 Types A convergent boundary is a boundary between 2 colliding plates. When 2 plates collide one plate may dive under the other plate at a Subduction Zone. There are 3 types. 1. Ocean – Ocean Convergence 2. Ocean – Continent Convergence 3. Continent – Continent Convergence

38. Force associated with Convergent Boundaries What type of force is associated with convergent boundaries? Compression

39. Ocean – Ocean Convergence • When two oceanic plates collide creating deep sea trenches. • Example: Marianas Trench the deepest part of the Pacific Ocean near the coast of Japan at at 11033 meters (36201 feet) deep. • Magma rises to form volcanoes or Island arcs on the ocean floor parallel to the trench.

41. Ocean to Continent Convergence • The Denser Oceanic plate descends into the less dense Continental Crust and SUBDUCTS its way down to the Asthenosphere. • Volcanoes may form • Ex: The Andes in South America were created when the Pacific plate ran into the South American plate creating the Andes Mountain Range.

43. New crust is continually being pushed away from divergent boundaries (where sea-floor spreading occurs), increasing Earth's surface. But the Earth isn't getting any bigger. What happens, then, to keep the Earth the same size? Subduction Zone In locations around the world, ocean crust subducts, or slides under, other pieces of Earth's crust. The boundary where the two plates meet is called a convergent boundary. Deep trenches appear at these boundaries, caused by the oceanic plate bending downward into the Earth.

45. Continent to Continent Conv. • Continental rocks have low densities in which neither is more dense than the other. This causes them to buckle up and create Mountains when they collide. • Very little volcanic activity. • Earthquakes are CoMmoN. • Ex: Appalachian’s and Himalayas

46. Convergent – Convergent boundary When two land masses meet neither will slide under the other. Instead, the two crush together at what is known as a convergent boundary. They crumple and fold. Some pieces of land are thrust over or under other pieces. The result is a mountain range.

47. The Himalayas, the highest mountains in the world, were created this way. (In fact, they're still growing.) So were the European Alps. Even the Appalachian Mountains formed when two land masses came together. Although with the Appalachians, the crushing ended long ago -- all that's left now are the eroded remnants of a once high mountain range.

48. Transform Fault Boundary • Boundaries where plates are sliding past one another in opposite directions or in the same direction but at different rates. • The Force associated with this boundary is Shearing. • Ex: San Andreas Fault in California. • YOU GET EARTHQUAKES !!!

49. Slippin' and a Slidin' Transform boundaries neither create nor consume crust. Rather, two plates move against each other, building up tension, then releasing the tension in a sudden and often violent jerk. This sudden jerk creates an earthquake.