SEA FLOOR SPREADING LAB BACKGROUND: In the 1950’s, detailed surveys began of the ocean floor and rift systems that circle the globe were discovered. These rifts were places where molten magma from the Earth’s mantle was breaking through and forming new crust. This formation of new crust and resulting movement of the ocean floor is a process called seafloor spreading. Much evidence has been found to support the idea of seafloor spreading. One major piece of evidence is the discovery of symmetrical bands (aka “zebra stripes”)of polarity in the oceanic crust on both sides of the mid-ocean ridges. When lava surfaces on the seafloor, it cools to form rocks. Many of these rocks contain the iron mineral magnetite and develop polarity based on the Earth’s magnetic orientation as they cool and become solid. Once a rock has cooled, its magnetic orientation is “frozen” and can serve as a permanent record of the earth’s polarity at that time. To detect this, scientists drag a magnetometer (MAD) across the ocean floor to detect magnetic rock deposits. Scientists can infer from this data the direction the earth’s magnetic poles were set at the time that that portion of the crust was formed. A major finding from these studies is that the sea floor is younger than any of the continents. Scientists are using the properties of magnetism to learn about the history of the ocean floor. This field of study is called paleomagnetism. 1. Create a model of an ocean rift. Arrange the magnets so they are alternating polarity. They do not need to be evenly spaced. Use your MAD (compass) to spread the magnets apart enough to see a flip in polarity 2. Seafloor diagram: Obtain a piece of adding machine tape TWICE as long as your model. Fold the tape in half Lay the adding machine tape over the magnets. Mark on the tape when the polarity flips. On the other half of the tape, mark the mirror image of the completed half (see diagram) Create “zebra stripes” on the adding machine tape. Color in the + stripes and leave the – stripes white. Attach the diagram to your lab. One diagram per 2 lab partners. ANALYSIS AND CONCLUSION: 1. On your seafloor diagram label “present day”. 2. On your seafloor diagram label the oldest stripes. Measure ½ of the present day polarity stripe in cm. ___________ cm 3. If on your seafloor diagram, .5cm= 10,000 years of crust formation, how long (in years) has the current polarity of the diagram been set to north? Show your work: 4. Describe, in detail, how the “zebra stripes” on the ocean floor formed. Use a minimum of 3 sentences. Use your own words. (see background) 5. Use the diagram above to calculate the rate the South Atlantic Ocean is expanding per year . (hint: rate= distance/time) Express your answer in centimeters. Show your work 6. Using your answer in #5, how many inches is the South Atlantic Ocean expanding per year? Show your work. 7. Using the diagram above, do magnetic reversals happen at regular intervals of time? Explain your answer. 8. Label the right side of the diagram above A thru F indicating the appropriate age of each strip. 9. Based on the diagram above, can you make a prediction concerning when the next reversal will occur? Explain your answer. 10. Using a highlighter, highlight where sea floor spreading is occurring on the map below: Do these areas contain young or old rock? Explain:

Sea Floor Spreading Lab

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