Continental Drift and Sea Floor Spreading

1. Continental Drift and Sea Floor Spreading

2. Lesson Essential Question • How does the theory of sea floor spreading support the continental drift hypothesis?

3. Concept/Voc Review • Science means “having knowledge”. • Scientific knowledge continues to change with new technology. • A hypothesis is a possible explanation for an event using what is known or observed. • A theory is an explanation of things or events based on knowledge from many observations or investigations.

4. Continental Drift • In 1912, Alfred Wegener, a German meteorologist , hypothesized that at one time all the continents were connected and have slowly moved to their current locations. • Wegener called this supercontinent Pangaea. • Wegener proposed various proofs

7. Puzzle –like fit of the continents-similar coastlines. • What else?

10. Fossil Evidence • Similar fossils found on different continents: • Animal fossil- aquatic reptile(Mesosaurus) found in South America/Africa • Plant fossil-Glossopteris(fern) found in S.A/AF/AUST/I/Antarctic

11. Making Connections • Why is the fact that similar fossils have been found on different continents considered evidence for continental drift? • If fossils of similar plants and animals are found on widely separated continents, it is more likely that the continents had once been joined rather than the plants and animals simply migrated to other locations.

13. Geologic Evidence • Similar rock structures are found on different continents. • Mountain ranges seem to end on one continent; pick up on next.

15. - Climate evidence as well • Warm weather plant fossils found in Arctic areas (Glossopteris) suggest continents had moved. • Glacier deposits found in tropical areas.

16. So how is this possible? • Wegener’s hypothesis was not accepted because he could not explain how or why the continents had moved.

17. Check-In • What are the four pieces of evidence Wegener used to support his continental drift hypothesis? • Geographic • Fossil • Geologic • Climatic

18. Pangaea BreakupLet’s see what Wegener proposed http://www.classzone.com/books/earth_science/terc/content/visualizations/es0806/es0806page01.cfm?chapter_no=visualization

19. Earth Science Read and Review Assignment • Read pages 272- 275 • On a piece of paper for turn –in: • Answer the reading check questions onpages:272 and 273. • Answer the Section Review Self Check questions 1-5 on page 275

20. Sea Floor Spreading?

21. The 1940’s& 50’s • In 1940’s, World War II lead to advances in sonar- using sound waves to detect submarines and map the sea floor. • In the 1940’ & 50’s scientist using sound waves(sonar)discovered an extensive system of underwater ridges or mountains, and valleys, stretching through the middle of the ocean floor.

22. Mid-Ocean Ridge They called these mid-ocean mountain ranges- Mid Ocean Ridges (MOR).

23. Sea Floor Spreading In the 1960’s Harry Hess , a Princeton Geology professor, suggested the theory of sea floor spreading to explain the ridges. • Hot, less dense material below Earth’s crust rises upward to the surface at the mid-ocean ridges. • Then, it flows sideways, carrying the seafloor away from the ridge. • As the seafloor spreads apart, magma (molten rock) moves up and flows from the cracks, cools, and forms new sea floor.

24. Sea Floor Spreading • http://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?chapter_no=visualization

28. Rock Samples • In 1968, research ship Glomar Challenger, collected rock samples from the Mid-Ocean Ridge(MOR). • The samples indicated the youngest rocks were located at the (MOR). • Rock samples became increasing older the further from the (MOR).

29. Age of Oceanic Crust Courtesy of www.ngdc.noaa.gov

30. Magnetic Clues • Scientist using a sensing device called a magnetometer have found that the earth’s magnetic field has reversed itself many times in the past. • Iron bearing rocks record the direction of the earth’s magnetic field when they formed. • These magnetic reversals showed that new rock was being formed at the mid-ocean ridge.

31. Magnetic Reversal animation http://www.classzone.com/books/earth_science/terc/content/visualizations/es0803/es0803page01.cfm?chapter_no=visualization http://www.edumedia-share.com/media.php?id=1325 http://www.pbs.org/wgbh/nova/magnetic/reversals.html

33. Evidence for Sea Floor Spreading • Rock sample dating found youngest rocks are located at mid-ocean ridges. • Magnetic reversals showed that new rock was being formed at the mid-ocean ridges.

34. Concept Check • How could sea floor spreading be related to continental drift? • If the seafloor is constantly spreading apart and moving, it will affect and move the continents.

35. Earth Science Read and Review Assignment • Read pages 276- 278 • On a piece of paper for turn –in: • Answer the reading check questions onpages:276 and 277. • Answer the Section Review Self Check questions 1-6 on page 278.

36. Check In • How is sea floor spreading different than continental drift?

37. The Structure of the Earth and Plate Tectonics

38. Lesson Essential Question • What is the theory of plate tectonics?

39. Vocab- Plate Tectonics • Earth’s crust and upper mantle are called the lithosphere. It is broken into sections called plates. • Plates move on the plastic-like layer of the earth’s mantle called the asthenosphere.

40. Plate Tectonics • The Earth’s crust is divided into 12 major plates which are moved in various directions. • This plate motion causes them to collide, pull apart, or scrape against each other. • Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. • The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.

41. World Plates

42. Structure of the Earth • The Earth is made up of 3 main layers: • Core • Mantle • Crust Mantle Outer core Inner core Crust

43. The Crust • This is where we live! • The Earth’s crust is made of: • Continental Crust • thick (10-70km)- buoyant (less dense than oceanic crust) - mostly old Oceanic Crust - thin (~7 km)- dense (sinks under continental crust)- young

44. What are tectonic plates made of? • Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle.

45. What lies beneath the tectonic plates? • Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.

46. So what makes plate tectonics work? Why are they moving? • Convection Currents- the heating, rising, cooling and sinking of magma(molten rock) within the earth.

47. Plate Movement • “Plates” of lithosphere are moved around by the underlying hot mantle convection cells.

48. Convection Current animations with plate movement • http://www.absorblearning.com/media/item.action?quick=12n

49. What happens at tectonic plate boundaries?

50. Divergent Convergent Transform Three types of plate boundary