Radiometric dating of drill core samples taken from the ocean floor just east of North Carolina revealed an age of about 160 million years (m. y). If average distance in kilometers from the coastal shelf of North America to the axis of the Mid-Atlantic Ridge is about 3,200 km, calculate the spreading rate (velocity) in cm/yr (assuming it is constant) of the Mid-Atlantic Ridge

The answer is 2 cm per year.

Explanation:

The spreading rate of the Mid-Atlantic Ridge would be: the average distance from the coastal shelf of North America to the axis of the Mid-Atlantic Ridge : estimated radiometric dating age.

So, the spreading rate = 3,200 km : 160 million years.

But 1 km = 100,000 cm, thus 3,200 km = 320,000,000 cm.

Therefore, spreading rate = 320,000,000 cm : 160,000,000 years = 2 cm per year.