15. a. We can get a rough estimate of how fast the rift zone in the Atlantic Oce
ID: 305072 • Letter: 1
Question
15. a. We can get a rough estimate of how fast the rift zone in the Atlantic Ocean is moving the continents of South America and Africa apart simply by assuming that 240 million years ago Natal, Brazil, and Douala, Cameroon, occupied the same neighborhood. These cities are presently 5000 km apart. How fast would they have to be moving, on average, to reach their present separation? Express your result in cm/year.
b. Another way to estimate the same quantity is by analyzing the convection cells in the mantle. If we assume that the convection cells are circular in shape with a diameter of 700 km, and that it takes 100 million years for a piece of rock to complete a trip around a cell, how fast is the rock traveling? How does this value compare to your previous results
Explanation / Answer
1
before 240 MA the cities were closed now they are 5000 kms apart so one city move almost 2500kms in 240 ma
the movement of plates in cm per year is 250000000 cm/240000000 year
= 25/24 = 1.04cm per year
2
the diameter of conventional circular cell 700kms
a rock complete its trip of circular cell with 100 ma
radius of cell 350 kms
cicumference of cell 2*3.14*350 = 700*3.14 =2198kms
plate movement in cm per year = 219800000cm/ 100000000 year
= 2.198 cm per year
the later result is more in comparision to earlier movement result.
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