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Name:______________________ Date:__________ Period:______ Lab – Sea Floor Spreading Introduction: Sea floor spreading is the hypothesis that the sea floor moves sideways away from the mid ocean ridge. The two sides of the ridge are moving in opposite directions leaving a rift valley that is the site of submarine volcanic eruptions. Molten rock from a magma chamber only 1 to 2 kilometers below the central rift valley feeds up to the spreading rift. The magma fills the crack between separating crustal plates. It is estimated that 20 volcanic eruptions occur each year along Earth’s mid ocean ridges and that every year 2.5 kilometers of new sea floor is formed in the process. Objective: Using data from the ocean floor, you will construct an ocean bottom profile. Vocabulary: Sea floor spreading – Mid ocean ridge – Subduction Rift valley – Harry Hess – Sonar – Continental shelf – Seamounts Procedure – Ocean Profile 1. Label the X-axis of the graph as “Distance from Coast (km)” 2. Label the Y-axis of the graph as “Depth (km)” 3. Using the data table provided, plot the data on the graph provided. 4. Label the following on the graph: mid ocean ridge, rift valley, continental shelf, deep ocean floor and sea mounts Procedure – Magnetic Stripes 1. Plot the data provided onto the graph provided as a bar graph. 2. If there is a North polarity for an age of the crust, color the bar as blue. 3. If there is a South polarity for an age of the crust, color the bar as red. Data – Ocean Profile Distance (km) 0 120 200 400 490 620 680 720 2000 2500 2900 3000 3090 3100 3200 Depth (km) 0 -0.2 -2.7 -3.7 -3.7 -4.6 -1.8 -4.6 -4.6 -4.0 -2.7 -1.8 -4.0 -2.4 -2.9 Distance (km) 3500 3600 3650 4025 4050 4100 4125 4500 5000 5300 5800 6000 6075 6100 ----- North Atlantic Ocean Bottom Profile Depth (km) -3.5 -3.7 -3.7 -4.0 -2.7 +0.5 -2.2 -4.6 -5.0 -4.4 -3.7 -2.7 -0.2 -0 ----- Data – Magnetic Stripes Polarity Changes Seen on the Ocean Bottom Analysis Questions: 1. What prominent sea floor feature is found in the central Atlantic Ocean? 2. What feature is found at a distance of 4,100 kilometers on the ocean bottom profile you constructed? 3. What motions create the rift valley? 4. What happens to the age of rocks as you move away from the ridge? 5. What do you observe about the polarity of rocks on both sides of the ridge? 6. Explain why looking at magnetic stripes provides evidence for sea floor spreading? 7. Crustal plates are estimated to move at a speed of 3 centimeters per year. How long will it take the plates to move 1 kilometer? Conclusion: Describe the features on the bottom of the sea floor and how they are created based on sea floor spreading. What is happening to the Atlantic Ocean? Pacific Ocean?