The magnetic declination at any given time can be frozen into a clay formation that contains magnetite and is heated above the Curie point.In general, many cultures used long-term fire hearths made of clay bricks, or a space lined with clay, that were baked into place by use.
Fortunately, there are other methods available to researchers.
These artifacts of occupation can yield the magnetic declination from the last time they were fired or used.
Archaeomagnetic dating was described in the 1992 publication “Paleomagnetism: Magnetic Domains to Geologic Terranes.” By Robert F. Archaeomagnetic dating requires an undisturbed feature that has a high likelihood of containing a remnant magnetic moment from the last time it had passed through the Curie point.
By cross-linking core samples from living and dead trees, a master sequence of annual tree-ring widths can be compiled.
Each region has its own unique master sequence since weather patterns are not the same from one area to another.