nov 10, 1965 - Harry Hess proposed the theory of seafloor spreading. The Mid-Atlantic Ridge was found in the 1960's. It is 40,000 miles long. Some evidence that supports Hess's theory is that rock closer to the ridge is younger, and as you get further away from the ridge is older. Another piece of evidence is that the seafloor is younger than the continents, that means older crust gets reabsorbed into the mantle. I used article 5. (Timeline)