An Introductory-Geology Exercise on the Polar-Reversal Time Scale

Abstract

The exercise provided gives students an opportunity to work with data related to Earth's magnetic polarity, and leads them through a series of tabulations, plots, and interpretations. The data consist of 150 sets, each of which includes a magnetic declination, an age, and a geographic location. The generalized sequence of class activities is as follows: 1) considering a question raised in the exercise; 2) plotting some aspect of the data; 3) interpreting the resulting plot, and; 4) going on to additional questions. Eventually the students are led to the conclusion that Earth's magnetic field has reversed itself periodically, and they then work out the magnetic reversal time scale for the last 4.5 million years. All materials necessary for the exercise are provided, including an instructor's guide, question and answer sheets, and graphs.