This article is about the study of paleomagnetism. For other uses, see Paleomagnetism (disambiguation).
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. Motonori Matuyama showed that the Earth's magnetic field reversed in the mid-Quaternary, a reversal now known as the Brunhes-Matuyama reversal.
One way to achieve the first goal is to use a rock coring drill that has a pipe tipped with diamond bits. The drill cuts a cylindrical space around some rock. This can be messy - the drill must be cooled with water, and the result is mud spewing out of the hole. Into this space is inserted another pipe with compass and inclinometer attached. These provide the orientations. Before this device is removed, a mark is scratched on the sample. After the sample is broken off, the mark can be augmented for clarity.
This page was last modified on 22 December 2015, at 01:44.