Editing Seafloor spreading (section)

==Continued spreading and subduction==
[[Image:Ridge render.jpg|thumb|300px|right|Spreading at a mid-ocean ridge]]
As new seafloor forms and spreads apart from the mid-ocean ridge it slowly cools over time. Older seafloor is, therefore, colder than new seafloor, and older oceanic basins deeper than new oceanic basins due to isostasy. If the diameter of the earth remains relatively constant despite the production of new crust, a mechanism must exist by which crust is also destroyed. The destruction of oceanic crust occurs at subduction zones where oceanic crust is forced under either continental crust or oceanic crust. Today, the Atlantic basin is actively spreading at the [[Mid-Atlantic Ridge]]. Only a small portion of the oceanic crust produced in the Atlantic is subducted. However, the plates making up the Pacific Ocean are experiencing subduction along many of their boundaries which causes the volcanic activity in what has been termed the [[Ring of Fire]] of the Pacific Ocean. The Pacific is also home to one of the world's most active spreading centers (the East Pacific Rise) with spreading rates of up to 145 ± 4&nbsp;mm/yr between the [[Pacific plate|Pacific]] and [[Nazca plate]]s.<ref>{{Cite journal|last1=DeMets|first1=Charles|last2=Gordon|first2=Richard G.|last3=Argus|first3=Donald F.|date=2010|title=Geologically current plate motions|journal=Geophysical Journal International|language=en|volume=181|issue=1|page=52|doi=10.1111/j.1365-246X.2009.04491.x|bibcode=2010GeoJI.181....1D|doi-access=free}}</ref> The Mid-Atlantic Ridge is a slow-spreading center, while the East Pacific Rise is an example of fast spreading. Spreading centers at slow and intermediate rates exhibit a rift valley while at fast rates an axial high is found within the crustal accretion zone.<ref name=":1" /> The differences in spreading rates affect not only the geometries of the ridges but also the geochemistry of the basalts that are produced.<ref>{{cite book|last=Bhagwat|first=S.B.|title=Foundation of Geology Vol 1|year=2009|publisher=Global Vision Publishing House|isbn=9788182202764|page=83|url=https://books.google.com/books?id=Fkw99wNiyQ0C&pg=PA83}}</ref>

Since the new oceanic basins are shallower than the old oceanic basins, the total capacity of the world's ocean basins decreases during times of active sea floor spreading. During the opening of the [[Atlantic Ocean]], sea level was so high that a [[Western Interior Seaway]] formed across [[North America]] from the [[Gulf of Mexico]] to the [[Arctic Ocean]].