What is the primary evidence that forms the basis of seafloor spreading? a. the rocks on the mid-oceanic ridges change densities in a symmetrical manner. b. the magnetic properties of rocks along the mid-oceanic ridges change alignment in a symmetrical manner. c. the rocks along the mid-oceanic ridges show age patterns in a symmetrical manner. d. the rocks along the mid-oceanic ridges have mineral patterns in a symmetrical manner.