as early as the 18th century, it was noticed that compass needles deviated near strongly magnetized outcrops. in 1797, von humboldt attributed this magnetization to lightning strikes (and lightning strikes do often magnetize surface rocks). in the 19th century studies of the direction of magnetization in rocks showed that some recent lavas were magnetized parallel to the earth's magnetic field. early in the 20th century, work by david, brunhes and mercanton showed that many rocks were magnetized antiparallel to the field. japanese geophysicist motonori matuyama showed that the earth's magnetic field reversed in the mid-quaternary, a reversal now known as the brunhes-matuyama reversal.