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older moving from south to north along the top of a mid-ocean ridge.no particular pattern of age with respect to the mid-ocean ridges.Therefore, if a volcano has produced many lava flows over a past period, scientists can analyze the magnetizations of the various flows and from them get an idea on how the direction of the local Earth's field varied in the past.Surprisingly, this procedure suggested that times existed when the magnetization had the opposite direction from today's. Click here to bring up four of those questions, with their answers.The strips on the Atlantic ocean floor, in particular, all seemed parallel to the "mid-Atlantic ridge." That is a volcanic ridge running roughly north-to-south (with some zigs and zags), halfway between Europe-Africa and America.It is marked by the focus-points of earthquakes and by some volcanic islands, and more recently it was explored by research submarines, which have at times observed lava oozing out at its crest.After Wegener died on an arctic expedition in 1930, only a handful of loyal supporters continued to promote his ideas.More evidence was needed, and it came from the Earth's magnetism.
Instruments can measure the magnetization of basalt.Not only were the magnetic strips lined-up with the central ridge, but their structure and distribution seemed remarkably symmetric on both sides: if (say) a narrow-wide pair of strips was observed at a certain distance east of the ridge, its mirror image was also found at about the same distance to the west.This puzzling picture was explained in 1962 by Lawrence Morley (whose article was rejected by the journals as too speculative) and by Drummond Matthews and Fred Vine.Each strip therefore represents an epoch of one or the other magnetic polarity, and the symmetry is also explained.It is as if the sea-floor was a giant tape recorder, with twin tapes emerging from the mid-Atlantic ridge, recording the Earth's magnetism at the time they emerge and then traveling in opposite directions.