How to Calculate Sea Floor Spreading

Map of Sea Floor Spreading Activity.

In the first half of the 1960s, evidence of the concept of sea floor spreading, resulted in the acceptance of plate tectonics. Dr. Robert Dietz, in 1961, and Dr. Harry Hess, in 1962, proposed the idea of sea floor spreading: the sea floor is continually created volcanically at mid-oceanic ridges and then spreads away, carrying the continents with them. Because of reversals of the Earth's magnetic field, the magnetic pattern of the sea floor can be used to date a piece of oceanic crust. Geologists at Smith College estimate that sea floor spreading throughout the world's oceans ranges between 1 centimeter per year and 10 centimeters per year.

Things You'll Need

• Calculator
• Map of the ocean floor displaying the age of the oceanic lithosphere
• Geographer's compass

Instructions

1. 

   Measure the distance from the center line of the spreading center (the black line in the middle of the red zone) and the border of the 65 MY (million year) point, at the boundary of the yellow and green zones. Sea floor spreading is usually measured in centimeters (cm) per year.

2. 

   Calculate the distance the plate has moved in the past 65 MY by converting the distance from the center line of the spreading center to the 65 MY point into centimeters. Since there are 100 cm per meter and 1,000 meters (m) per kilometer, there are 100,000 cm per kilometer (km). If the distance between the spreading center and the 65 MY point on the map was 3 cm, and the scale of the map is 1 : 500 (1 cm = 500 km), then 3 cm x 500 km = 1,500 km = 150,000,000 cm.

3. 

   Convert the length of time that the tectonic plate has been moving into scientific notation, for the sake of simplicity. In this case, we have already determined that the plate has been moving for 65 million years, which in scientific notation is 6.5 x 10e7 years.

4. 

   Calculate the rate of sea floor spreading, R, by dividing the distance (d) moved, 150 million centimeters, by the time (t) to move those 150 million centimeters:
   R = d/t or R =1.5 x 10e7 cm / 6.5 * 107 years = 2.30 cm/yr

Tips & Warnings

• Exponential notation is recommended because of the size of the numbers in use.

References

• Calculating Sea Floor Spreading
• Robert Van Der Hilst, PhD; Professor of Earth, Atmospheric and Planetary Sciences, MIT; Cambridge, Mass.

Resources

• Drifting Continents and Colliding Paradigms