Rate of Spreading = distance the sea floor moved / length of time
or R = d/t

Generally expressed as cm/yr

Source: http://www.geo.cornell.edu/geology/classes/Geo101/graphics/ocean_crust_age.gif

1 km = 1000 m

1 m = 100 cm

so 1 km = 100,000 cm or 10⁵ cm

1. For the North Atlantic Ocean (using the map in the lab)

• Measure the distance between the center of the spreading center (red) and the border between dark yellow and light green (65 Ma point)
  • I measured 2 cm
• 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
  • 2 cm * 475 km/cm = 950 km = 95,000,000 cm = 9.5 * 10⁷ cm
• Determine the length of time that the plate has been moving
  • 65 million years = 65,000,000 years = 6.5 * 10⁷ years
• Use the above equation to calculate spreading rate
  • R = d/t or R = 9.5 * 10⁷ cm / 6.5 * 10⁷ years = 1.46 cm/yr

Notes: Ranges of Spreading throughout the world's oceans: 1cm/yr to 10 cm/yr

Measure from the center of the spreading center to a known age point on the plate rather than from 65 Ma on the eastern plate to 65 Ma on the western plate. Why? Because you want to know how fast 1 plate has moved.