I doubt this will work. When magnets or magnetic rocks are heated, like in this fire, they lose their magnetization.

Turner is overreaching. The magnetic field is what protects ISS LEO astronauts from the solar wind, in our case the atmosphere seems to be the sufficient protection (compare almost field less Venus).

@ WP: They did find a resulting re-magnetization. I suspect not all grains will demagnetize, too uneven temp.

Ah yes, thanks Doug!

Still, useless for assessing paleomagnetism further back than one to two thousand years, if that much. Probably no further back than the last time the firepit was used --say, Superbowl XLVI?

Probably have better luck using the sedimentary record.