magnetic epoch


noun
  1. geology a geologically long period of time during which the magnetic field of the earth retains the same polarity. The magnetic field may reverse during such a period for a geologically short period of time (a magnetic event)

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012