describing how the rate of sea-floor speading is calculated

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"Describe how the rate of sea-floor spreading may be calculated. Evaluate the
accuracy you any methods you describe." (25 marks)
First of all a by paleomagnitism via the identification of
magnetic anomalies it is possible to calculate the rate of
sea floor spreading. This works because about every
50,000 years the magnetic poles of the Earth reverse. As
basalt is erupted from sea floor from a mid-oceanic ridge,
the iron in the basalt aligns itself to the magnetic pole
orientation, see figure 2. When plotting these it forms a
black and white graph shown in figure 1.
By working out the dates of the rocks via
radiometric dating, K-Ar , it is possible to
calculate the rate of spreading by using the
speed, distance, time calculation.
Rate of Spreading = distance the sea floor
moved / length of time
or R = d/t
Generally expressed as cm/yr
This method is good because it allows
accurate results but it is very expensive to keep on taking samples from the sea floor and calculating
the radioactive decay of the argon with in the minerals. It is also impractical because it would be
impossible to be able to take a big enough sample because the sea floor doesn't spread at the same
rate all along the plate boundary.
Another method is to use a map of the ocean floor showing known ages of parts of the sea floor
using satellites to take images and track the movement of trackers attached to the sea floor giving
images as show in fig 3.

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Figure 3: ages of sea floor rocks
Measure the distance between the centre of the spreading centre (red) and the border
between dark yellow and light green (65 Ma point)
Since the scale on the map is 1 cm = 475 km, calculate the real distance that the plate has
moved over the past 65 Ma
Determine the length of time that the plate has been moving by using the equation…read more


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