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 centimetre per year and 10 centimetres per year.
- Skill level:
- Moderately Challenging
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Things you need
- Map of the ocean floor displaying the age of the oceanic lithosphere
- Geographer's compass
Measure the distance from the centre line of the spreading centre (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 centimetres (cm) per year.
Calculate the distance the plate has moved in the past 65 MY by converting the distance from the centre line of the spreading centre to the 65 MY point into centimetres. Since there are 100cm per meter and 1,000 meters (m) per kilometre, there are 100,000cm per kilometre (km). If the distance between the spreading centre and the 65 MY point on the map was 3cm, and the scale of the map is 1 : 500 (1cm = 500km), then 3cm x 500km = 1,500km = 150,000,000cm.
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.
Calculate the rate of sea floor spreading, R, by dividing the distance (d) moved, 150 million centimetres, by the time (t) to move those 150 million centimetres: R = d/t or R =1.5 x 10e7 cm / 6.5 * 107 years = 2.30cm/yr
Tips and warnings
- Exponential notation is recommended because of the size of the numbers in use.
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