<Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (April 2015) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (April 2015) (Learn how and when to remove this template message) </Td> </Tr> <P> In the general case, sea floor spreading starts as a rift in a continental land mass, similar to the Red Sea - East Africa Rift System today . The process starts by heating at the base of the continental crust which causes it to become more plastic and less dense . Because less dense objects rise in relation to denser objects, the area being heated becomes a broad dome (see isostasy). As the crust bows upward, fractures occur that gradually grow into rifts . The typical rift system consists of three rift arms at approximately 120 degree angles . These areas are named triple junctions and can be found in several places across the world today . The separated margins of the continents evolve to form passive margins . Hess' theory was that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge . </P> <P> If spreading continues past the incipient stage described above, two of the rift arms will open while the third arm stops opening and becomes a' failed rift' . As the two active rifts continue to open, eventually the continental crust is attenuated as far as it will stretch . At this point basaltic oceanic crust begins to form between the separating continental fragments . When one of the rifts opens into the existing ocean, the rift system is flooded with seawater and becomes a new sea . The Red Sea is an example of a new arm of the sea . The East African rift was thought to be a "failed" arm that was opening somewhat more slowly than the other two arms, but in 2005 the Ethiopian Afar Geophysical Lithospheric Experiment reported that in the Afar region last September, a 60 km fissure opened as wide as eight meters . During this period of initial flooding the new sea is sensitive to changes in climate and eustasy . As a result, the new sea will evaporate (partially or completely) several times before the elevation of the rift valley has been lowered to the point that the sea becomes stable . During this period of evaporation large evaporite deposits will be made in the rift valley . Later these deposits have the potential to become hydrocarbon seals and are of particular interest to petroleum geologists . </P>

Similarities between sea floor spreading and continental drift