Name _________________________________ 38. How can volcanoes be destructive? 39. How can volcanoes be beneficial? Period _____ Code # _____ 40. What was Alfred Wegener's theory about Earth's continents? Alfred Wegener, a german meteorologist and astronomer, proposed that in the distant past Earth’s continents were all joined as a single landmass. 41. What caused the jigsaw puzzle effect to occur? 42. What did Wegener say would occur if the continents were brought back together again? 43. What did Wegener call his idea of moving landmasses? 44. What did fossils and analysis of radioactive materials show about the ocean floor? 45. Describe the term " patterns of magnetic polarity". 46. While rock was still molten, what did the iron particles do in order to create this pattern of magnetic polarity? 47. What have scientists discover about the Earth's magnetic poles every 100,000 years? 48. Where are oceanic crust created and destroyed? 49. Define tectonics. 50. According to the theory of plate tectonics, what is the Earth's surface composed of?