geomagnetic field reversal

geomagnetic field reversal

[¦jē·ō·mag¦ned·ik ′fēld ‚ri‚vər·səl]
(geophysics)
Reversed magnetization in sedimentary and igneous rock, that is, polarized opposite to the mean geomagnetic field.
References in periodicals archive ?
And when continents were more evenly arranged--such as between about 80 million and 120 million years ago, and again between 260 million and 310 million years ago--there were long stretches without geomagnetic field reversals.
Such geomagnetic field reversals occur every couple hundred thousand years, normally taking about 4,000 years.