GARY HINCKS / SCIENCE PHOTO LIBRARY GARY HINCKS / SCIENCE PHOTO LIBRARY
Seafloor spreading, artwork. Seafloors spread when magma rises up at mid-ocean ridges. The magma heats the surrounding rocks, which expand to form the ridges. The seafloor spreads away from the ridges due to pressure from the cooled magma that forms in the centre of the ridge. Some theories, however, hold that it is the pull from descending magma at the plate's edge that pulls the ridge apart. Seafloor spreading was detected in the 1960s and was immediately recognised as the process that drives continental drift, and proved the theory of plate tectonics. The forces create volcanic islands (centre right) that slowly get eroded to submerged seamounts (centre left) and guyots (left) over time.
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