Who Was Alfred Wegener

1. Who Was Alfred Wegener • German meteorologist (person who studies the weather) • Most research dealt with proving the existence of the jet stream • Became famous for his Continental Drift Hypothesis

2. What is the Continental Drift Hypothesis • All continents were together in one landmass • Landmass was known as Pangaea • Some natural event happened and caused the continents to split • Continents drifted apart to their current day position

3. Continental Drift Hypothesis

4. Pangaea Animation • http://www.youtube.com/watch?v=hSdlQ8x7cuk

5. What type of evidence did he use to support his hypothesis? • The continents seems to fit together like a puzzle • One large land mass known as Pangaea • Lauratania – North America, Europe, Asia • Gondwana – South America, Australia, Africa, Antarctica, India

6. What type of evidence did he use to support his hypothesis? • Geologic Evidence: • Similar rock formations found on different continents • These formations were the same age • Different mountain ranges line up and have similarities

7. What type of evidence did he use to support his hypothesis? • Fossil Evidence: • Four index fossils were found throughout the five southern continents • Prime example: Glossopteris – type of tropical fern • Most animals were fresh water or land dwellers and couldn’t swim long distances

8. What type of evidence did he use to support his hypothesis? • Climatic Evidence • Coal Beds: indicate tropical climates and were found in Antarctica • Fossils indicate animals lived in tropical ecosystems • Glacial deposits (moraines) on different continents are similar by positioning and material • Glacial striations or scratch marks follow same trends on different continents

9. Climate Evidence

10. Was Wegner’s Hypothesis accepted? NO!!!!

11. Why wasn’t Wegner’s Hypothesis accepted? • Wegner had an abundance of evidence to support his hypothesis • Didn’t have the mechanism to explain how the continents divided

12. Bill Nye Video • http://www.youtube.com/watch?v=GyMLlLxbfa4

13. History of Science • Until the mid-1900’s scientists thought the bottom of the ocean was flat • World War II – the development of technology • New sonar technology surveyed the ocean floor • Harry Hess – Geologist and Navy Officer who had to study these sonar scans • The ocean floor in not flat • Mountain range at the bottom of the ocean

14. What is a Mid Ocean Ridge? • sonar scans showed that there was a 12,000 mile mountain range at the bottom of the ocean • Most famous part = Mid Atlantic Ridge • Volcanic activity is happening in this area under the water • Ridges can stand over a mile tall underneath the water

15. Sonar

16. What is the big deal about mid-ocean ridges? • Hess built upon the continental drifty hypothesis • Hess proposed that the continents separated due to sea floor spreading • Sea floor spreading occurred at the MOR’s

17. Sea Floor Spreading • Magma moves upward and out of cracks in the seafloor. • As it hardens on the surface, new seafloor forms. • Older seafloor is pushed away from the edge.

18. First Line of Evidence from Hess • Hess tested core samples (sediment/rock) ages • The farther from the mid ocean ridge (MOR), the older the rocks were • Pattern remained consistent on both sides of the MOR

19. Core Samples and Radiometric Dating Isochronal Map

20. What was Hess’ other line of evidence • Paleomagnetism: magnetic direction acquired by the minerals in a rock at the timetherockwasdeposited or hardened • Affected by the location of Earth’s North Pole • Normal positioning and reversed positioning

21. How does paleomagnetism work in sea floor spreading • Magma/lava has a high iron content • Iron is affected by Earth’s magnetism • As the magma plumes from the opening in the ridge, it hardens to lava • The iron in ocean rocks point to the magnetic North Pole • Magnetic North Pole moves and/or reverses randomly over time

22. Paleomagnetism Simulation • http://oit.williams.edu/itech/learning-objects/

23. How does paleomagnetism work in sea floor spreading? • Direction of iron follows the same trends on both sides of the MOR • Age correlation with iron trends • Rock ages and magnetic field direction changes sea floor spreading along the MOR’s

24. Earth’s Crust Oceanic Continental Makes up the land/continents on Earth Composed of mostly Granites Thick – 20-70 km thick Density – 2.7 g/mL • Makes up the ocean floor • Composed of pillow basalts (rock type) • Thin – 5 km thick • Density – 3.0 g/mL

25. How are continental and oceanic crust similar? • They both have similar chemical compositions

26. How are continental and oceanic crust similar? • They both have similar chemical compositions • Make up an area known as the Lithosphere

27. How are continental and oceanic crust similar? • They both have similar chemical compositions • Make up an area known as the Lithosphere • Are broken up into pieces known as tectonic plates

28. Where does plate tectonics work?

29. Important Layers for Plate Tectonics • Two sub-layers that drive plate tectonics: • Lithosphere • Asthenosphere • Lithosphere: Crust and rigid upper most part of the mantle = tectonic plate • Asthenosphere: plastic layer within the upper mantle that contains the mechanisms to cause plate movement

30. Making of the Theory of Plate Tectonics • http://www.youtube.com/watch?v=6CsTTmvX6mc

31. How did the Theory of Plate Tectonics come about? • Merger of all evidence: • Wegener’s continental drift hypothesis evidence • Hess’ sonar scans, core sample ages, paleomagentism to form sea floor spreading • Geographic evidence: mountain ranges, volcanoes, island arcs, trenches, MOR’s • Earthquake data

32. Divergent Boundary • Plates move apart AKA sea floor spreading • Occurs along mid ocean ridges in oceans • Can happen on land; lead to the break up of Pangaea • Rift Valley – a linear shaped lowland caused by the movement of the land away from one another

33. Rift Valley

34. Rift Valley….Remember?

35. Divergent Boundaries

36. Convergent Boundaries • Subduction occurs • Denser plate goes under the less dense plate • Intense pressure and heat melts subducting plate • Hess’ crustal recycling process

37. Convergent Boundary

38. Convergent Boundaries • Three types: • Continental vs. Continental • Oceanic vs. Oceanic • Continental vs. Oceanic

39. Oceanic – Oceanic Subduction • Subduction of two oceanic plates • Denser older oceanic plate subducts under younger less dense • Lots of volcanism and earthquakes • Island Arc and deepest trenches are formed Examples: Aleutian Islands and Japan

40. Continental – Oceanic Subduction • Subduction of denser oceanic plate under the continental • Continental plate has a lower density • Uplifts the land around the coast • Volcanoes and strong earthquakes occur at these regions • Example: Ring of Fire (Around the Pacific Ocean)

41. Continental – Continental Collision • When two continental plates/crust collide • Both plates have similar densities • Land buckles and pushes up • Push up motion of land = uplift • Lots of heat and pressure change the rocks • Forms mountain ranges and many Earthquakes • Example: Himalayas

42. Transform Boundary • When two plates slide past each • Transform Fault and Strike Slip Fault • Occurs on land and in the ocean along the MOR’s • Many earthquakes • Prime Example: San Andreas Fault

43. Transform Boundaries

44. How do the tectonic plates move apart? • Convection currents move the tectonic plates • Occurs in the asthenosphere • Pertains to how magma responds to heating, pressure, cooling, and density fluctuations

45. How do Convection Currents operate in the Asthenosphere? • Heat from the Core heats the magma in asthenosphere • Magma rises to boundary with Crust • Pressure breaks Crust and magma forms new oceanic crust • Most magma is trapped and moves underneath the Crust away from heat

46. How do Convection Currents operate in the Asthenosphere? • As the magma moves under the Crust, it moves the tectonic plate as it cools • Cooling process cause magma’s density to increase • Cooled dense magma starts to sink • Sinking occurs when plates subduct – slab pull

47. Diagram this picture