1. The magnetic field of Earth has had (3,5, 7) intervals of reversed polarity during the past 4 million years. Circle your answer. 2. Approximately how long ago did the current normal polarity begin? years ago. One and a half million years ago, a compass needle would have pointed to the (North,South). Circle your answer. 3. The period of normal polarity, c, began (1,2, 3) million years ago. Circle your answer. 4. During the past 4 million years, each interval of reverse polarity has lasted (more, less) than 1 million years. Circle your answer. The records of the magnetic polarity reversals that have been determined from the oceanic crust across sections ofthe midocean ridges in the Pacific, South Atlantic, and North Atlantic oceans are shown in Figure 10.5. As new ocean crust forms along the midocean ridge, it spreads out equally on both sides of the ridge. Therefore, a record ofthe reversals is repeated. Notice that the general pattern of polarity reversals in Figure 10.4 can be matched with the polarity ofthe rocks on either side ofthe ridge for each ocean basin in Figure 10.5. Use Figures 10.4 and 10.5 to answer questions 5-7. Questions for Figure 10.5: 5. Using the distance scale in Figure 10.5, the (Pacific, South Atlantic, North Atlantic) has spread the greatest distance during the last 2 million years. Circle your answer. 6. Refer to the distance scale in Figure 10.5. Notice that the left side of the South Atlantic basin has spread approximately 39 kilometers (km) from the center of the ridge crest in 2 million years. a. How many kilometers has the left side ofthe Pacific basin spread in 2 million years? km b. How many kilometers has the left side ofthe North Atlantic basin spread in 2 million years? km The distances in question 6 are for only one side ofthe ridge. Assuming that the ridge spreads equally on both sides, the actual distance each ocean basin has opened would be twice (2 x ) this amount. 7. How many kilometers has each ocean basin opened in the past 2 million years? a. Pacific Ocean basin km b. South Atlantic basin km r- hlnrth Atlantir' hacin l(m