The seafloor mid-ocean ridge system encircles our planet for more than 40,000 miles. Yet this remarkable planetary feature is almost totally unseen above the oceans' surface. An exception is Iceland, where the ridge passes right through that nation.
"Ridge" is used to describe this mega-feature that in places rises several thousand feet above the seafloor. The system is actually two parallel ridges with a rift valley running between them that can be as much as 180 miles wide. It is here that the Earth's crust is being perpetually created anew.
Parts of this great mountain range were first discovered on the Atlantic seafloor in the 1950s. At first, it was thought to be unique to that ocean. Then, as more surveys were done, it was eventually determined that this was one continuous global feature linked to geological processes constantly changing the face of our planet.