Heezen noticed that ocean earthquake epicentre data also formed long lines - in fact, when one map was placed above the other on a light table the earthquakes formed near continous lines along the Mid-Atlantic ridge right where Tharp had indicated a rift valley. Using earthquake data to extrapolate & plot the rift position they found that the rift extended landward into the Rift Valley of East Africa. Heezen was convinced. 🧵4/5