How do sea-floor spreading and magnetic reversal produce bands…?
When magma rises to fill in the gap, it contains magnetic elements. In 1963, Fred Vine, Drummond Matthews, and others found that the crust surrounding the midocean ridges showed alternating bands — each band magnetized with a polarity opposite the surrounding bands. They suggested that as new sea-floor crust was formed around the rift in the midocean ridge, it magnetized differently, depending upon the polarity of the planet at that time. This supported the theory that Harry Hess had put forth, that the ocean progressivley widens as new sea floor is created along a crack that follows the crest of midocean ridges. Molten rock erupts along a mid-ocean ridge, then cools and freezes to become solid rock. The direction of the magnetic field of the Earth at the time the rock cools is “frozen” in place. This happens because magnetic minerals in the molten rock are free to rotate so that they are aligned with the Earth’s magnetic field. After the molten rock cools to a solid, these minerals c
