At mid-ocean ridges, the seafloor is spreading as the plates move away from each other.
Harry Hess said tha thte continents move over time but not in a random drifting pattern. Instead the seafloor was spreading at the mid-ocean ridge because the plates were moving away from each other. Motion of t heseafloor in a conveyor belt fashion explains the phenomena of the youngest rocks being found only at the mid-ocean ridges, and rockes getting progressively older as you move away from the ridge.
I hope this explains :)
