In the Geologic Past,the Polarity of Earth's Magnetic Field Is

Multiple Choice

In the geologic past,the polarity of Earth's magnetic field is ________.

A) unknown,but it is assumed to have been identical to today's
B) known to have stayed constant through geologic time,as shown by remnant magnetization of iron-rich minerals in rocks
C) known to have experienced numerous reversals,as shown by remnant magnetization of iron-rich minerals in rocks
D) known to have stayed constant through time,based on theoretical calculations