1. Assume that the spreading north pole for the North American Plate corresponds exactly with the geographic north pole of the Earth and determine horizontal spreading rates at 5 different locations on the Mid-Atlantic Ridge if the angular speed () of the North American Plate is 1.010-8 radians per year. How do your calculations compare with GPS-determined rates for the North American Plate, and what are the implications of your findings?

2 .Assume that Alfred Wegener was right, and North American and Europe were joined 200 million years ago and that the current distance between the continents is approximately 5585 km. Based on this information, what has been the average horizontal spreading rate at the Mid-Atlantic Ridge over the last 200 million years? How does this rate compare with other rate measurements?

3. Use equation 4-2-1 to show how the depths of the ocean bottom at 20, 40 and 60 million years of age would change as a result of changes in the thermal diffusivity of the crust. What are the implications of your results?

4. Given that the surface area of the oceans is approximately 361,000,000 km2, use the histogram of ocean area vs. depth (Figure 4-15) to estimate the total volume of the oceans. How does your result compare with the known ocean volume of 1,338,000,000 km3?

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