Question: How did the Mid-Atlantic ridge come into existence?

Hannah Bentham answered on 24 Jun 2013:

Great question!

The mid-Atlantic ridge was formed from the break up of the super-continent Pangea, where the Americas, Europe and Africa land masses were all attached neighbours. Pangea was formed about 300 million years ago, and the break up started about 200 million years ago. Scientists believe the break up starting along three fissures that grew between Africa, South America, and North America. As magma welled up through the weakness in the crust, this created a volcanic rift zone. The gap between the spreading continents gradually grew to form a new ocean basin, the Atlantic. The rift zone known as the mid-Atlantic ridge continued to provide the raw volcanic materials that allowed the ocean basin to keep expanding. If you look at the Atlantic on google maps satellite, you can see that the mid-Atlantic Ridge is jaggered. These are lots of transform faults that are perpendicular (90degress) to the ridge that form to accommodate the large stresses.

Geologists do not know all the mechanisms about how rifting first starts. Many scientists are studying the rifting process in Afar, Ethiopia and try to use those findings will other rifting episodes.