SEAFLOOR SPREADING
Station 1: Bathymetric and Radiometric Evidence of Seafloor Spreading
Observation Statements:
1. Examine Graph 1 of the distance from the Mid-Ocean ridge and the ocean depth. Provide an interpretation of what the graph is indicating.
2. Examine Graphs 2A and 2B of the crust age and the distance to the ridge. Provide an interpretation of what the graph is indicating.
3. Compare Graphs 2A and 2B of the crust age and the distance to the ridge. Are there any differences between the shapes of the curves? If so, provide an explanation as to what is causing the difference.
4. Examine Graphs 3A and 3B of the crust age and ocean depth. Provide an interpretation of what the graph is showing.
5. Compare Graphs 3A and 3B of the crust age and ocean depth. Are there any differences between the shapes of the curves? If so, provide an explanation as to what is causing the difference.
Observation statement: Using the equation of velocity, calculate in centimeters per year: 1) the spreading rate of the Pacific Ridge and 2) Atlantic Ridge. Use data provided to you earlier in Station 1 for the Pacific and Atlantic Ocean. Show all work and do not forget your units.
1. Spreading rate of seafloor at Atlantic Ridge
2. Spreading rate of seafloor at Pacific Ridge
Observation statement: Using the data obtained from the sea floor depth and age plotted graphs you will need to estimate the AGE of the ocean crust in the Pacific using the line of best fit in Graph 3B. (Approximate years only.)
Depth Age
3,000 m/9,840 ft ______
3,300 m/10,827 ft ______
3,600 m/11,811 ft ______
3,900 m/12,795 ft ______
Station 2: Use of Sediment Thickness Patterns as Supporting Evidence of Seafloor Spreading
Observation Statements
1. After completing the plot of sediment thickness and distance from the ridge what pattern do you observe?
2. After completing the plot of sediment thickness and sediment age what pattern did you observe?
Analysis of Results:
Interpret and analyze your results for each Station by answering the following questions.
Station 1: Bathymetric and Radiometric Evidence of Seafloor Spreading
1. Based on the plotted graphs you constructed, provide an explanation as to what is causing the age of the crust to increase the further away from the ridge.
2. Provide a possible cause that explains the difference in spreading rates between the Atlantic and Pacific mid-ocean ridges.
3. Provide an explanation as to why the seafloor increases in depth away from the ridge, and why it tends to level out at great distances away from the ridge.
Station 2: Use of Sediment Thickness Patterns as Supporting Evidence of Seafloor Spreading.
1. Provide an explanation of the sediment thickness pattern you observed in your graph from Station 2.
2. Would you expect the sediment thickness away from the ridge to perfectly show the sedimentation rate based on age? For example if the sediment rate is 1mm every 1000 years would you expect that a 100,000-year-old crust would have exactly 100 mm of sediment on top of it?
Station 3: Paleomagnetic Banding as Supporting Evidence of Seafloor Spreading
1. Provide an explanation that supports the magnetic banding observed in the profile you drew in Station 3
2. Why does the magnetic banding profile show such strong evidence for seafloor spreading?
3. Based on the observed data of magnetic reversals, what seems to be the average number of years between the actual flips?
4. Based on your magnetic profile do you think that mid-ocean ridges around the world would show magnetic profiles that would be exactly the same? Explain your answer.
Conclude and Communicate:
1. Present an explanation that would account for the differences in the plotted data graphs between the Pacific and Atlantic data that was provided to you.
2. If a mid-ocean ridge was to stop its production of oceanic crust, in other words the ridge becomes dormant or dies out, what would you expect to observe with the sediment thickness at the site of the ridge? Explain.
3. If new ocean floor is constantly being produced at mid-ocean ridge systems, then how is it that our planet's crust is not getting larger and the magma in the asthenosphere is not being emptied as time progresses?
4. Recently magnetic banding patterns have been found on the surface of Mars by orbiting probes carrying magnetometers. What conclusions can be made by this discovery?
5. How important is it that we have found some evidence of dynamic crusts on other worlds? Does this strengthen or weaken the support for seafloor spreading and continental drift on Earth? Explain.
6. Write two new research questions based on what you learned from this activity.