File:Geomagnetic dipole moment estimated from 500-year global averages of measurements on lava flows and archeological materials, such as bricks and pottery.jpg

Summary
A chart showing the geomagnetic dipole moment using 500-year averages from lava flows and archaeological digs.

Source: http://www.talkorigins.org/faqs/dalrymple/creationist_age_earth.html#h33