The seafloor spreading hypothesis was based primarily on the magnetic mapping evidence. It was also supported by several additional lines of evidence available at the time including evidence from age dating and bathymetric surveys. At or near the crest of the mid- ocean- ridges the seafloor crustal lavas were shown to be very young and these lavas become progressively older when moving away from the ridge crests, as shown below in Mollweide equal area projection of the completed Geological Map of the World
Geological Map of the World showing the distribution of the various ages of rocks occurring beneath the layer of surface soils or seafloor sludge.
This suggested that the Earth’s magnetic field has reversed many times throughout its history. By explaining both the zebra- stripe like magnetic patterns and the construction of the mid- ocean- ridge system the seafloor spreading hypothesis quickly gained converts. Furthermore, this seafloor mapping is now universally appreciated to be a natural tape recording of both the history of the reversals in the Earth’s magnetic field and opening of each of the oceans.