tectonicsII

tectonicsII - Physical Geology 101 4. Plate Tectonics II...

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Physical Geology 101 4. Plate Tectonics II (p. 46-67) Seafloor Spreading In the early 1960s, samples of basaltic ocean crust were dredged up from various locations across the ocean basins. The samples were then analyzed to test for their _____________ properties, which led to the discovery of something quite intriguing. What was discovered about the magnetic properties of the ocean floor rocks as you move further and further away from a mid-ocean ridge? ________________________________________________________________________ The magnetic polarity that is the same as what exists currently on Earth is called ________ polarity (i.e., compasses point towards current-day magnetic north). The magnetic polarity that is the opposite of what exists currently on Earth is called ____________ polarity (i.e., compasses would point towards current-day magnetic south). Are paleomagnetic reversals seen in rocks of all the Earth s oceans? YES or NO What was discovered about the pattern of magnetic reversals on one side of a ridge compared to the opposite side of the ridge? ______________________________________ The evidence suggested that new basaltic crust must have been generated at the ridge and then been pushed to either side at a later time when the next cycle of lava got squeezed out of the middle of the ridge. As each new cycle of basaltic lava erupted, it cooled and preserved a record the Earth s magnetic field in the magnetic minerals inside the rock. So why does the paleomagnetic field recorded in the ocean rocks change through time? _______________________________________________________________ How often does the magnetic pole switch happen on Earth? _______________________ So the ocean floor acts like a conveyor belt, carrying volcanic rocks to either side of the ridge further and further away from each other as new material forms at the ridge. What happens to the continents during this whole process? ________________________________________________________________________ In other words, the continental and oceanic crust move together , rather than the continents plowing through the oceanic crust. This is how continental drift happens. Individual continents start out as a single continent that tears apart; then
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tectonicsII - Physical Geology 101 4. Plate Tectonics II...

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