Editing Seafloor spreading (section)

==Debate and search for mechanism==
At the Mid-Atlantic Ridge (and in other mid-ocean ridges), material from the upper [[Mantle (geology)|mantle]] rises through the faults between oceanic plates to form new [[Crust (geology)|crust]] as the plates move away from each other, a phenomenon first observed as continental drift. When [[Alfred Wegener]] first presented a hypothesis of continental drift in 1912, he suggested that continents plowed through the ocean crust. This was impossible: oceanic crust is both more dense and more rigid than continental crust. Accordingly, Wegener's theory wasn't taken very seriously, especially in the United States.

At first the driving force for spreading was argued to be convection currents in the mantle.<ref>{{Cite journal|last=Elsasser|first=Walter M.|date=1971-02-10|title=Sea-floor spreading as thermal convection|journal=Journal of Geophysical Research|language=en|volume=76|issue=5|pages=1101–1112|doi=10.1029/JB076i005p01101|bibcode=1971JGR....76.1101E}}</ref> Since then, it has been shown that the motion of the continents is linked to seafloor spreading by the theory of plate tectonics, which is driven by convection that includes the crust itself as well.<ref name=":2" />

The driver for seafloor spreading in plates with [[active margin]]s is the weight of the cool, dense, subducting slabs that pull them along, or slab pull. The magmatism at the ridge is considered to be passive upwelling, which is caused by the plates being pulled apart under the weight of their own slabs.<ref name=":2">{{Cite journal|last1=Forsyth|first1=Donald|last2=Uyeda|first2=Seiya|date=1975-10-01|title=On the Relative Importance of the Driving Forces of Plate Motion|journal=Geophysical Journal International|language=en|volume=43|issue=1|pages=163–200|doi=10.1111/j.1365-246x.1975.tb00631.x|issn=0956-540X|bibcode=1975GeoJ...43..163F|doi-access=free}}</ref><ref>{{cite journal|doi=10.1038/311615a0|title=India–Eurasia collision chronology has implications for crustal shortening and driving mechanism of plates|year=1984|author=Patriat, Philippe|journal=Nature|volume=311|pages=615|last2=Achache|first2=José|issue=5987|bibcode = 1984Natur.311..615P |s2cid=4315858}}</ref> This can be thought of as analogous to a rug on a table with little friction: when part of the rug is off of the table, its weight pulls the rest of the rug down with it. However, the Mid-Atlantic ridge itself is not bordered by plates that are being pulled into subduction zones, except the minor subduction in the [[Lesser Antilles]] and [[Scotia Arc]]. In this case the plates are sliding apart over the mantle upwelling in the process of ridge push.<ref name=":2" />