Magnetic Archaeology? Yeah, I made a weird face when I read it the first time too. But it's real, I swear. The technical term is: archeomagnetic dating, a process built around two phenomena: when heated, magnetic particles reorient themselves to magnetic north; and over time, magnetic north is, literally, all over the map.
Seems that, as time passes, magnetic north moves on this wibbly wobbly world of ours. This fascinating, and fairly new, technique of using that phenomenon to date artifacts is being used on Pawnee Indian artifacts from a dig in Kansas. Using heat the specimens are slowly, and in progressing stages, demagnetized until only the base magnetism is left. What this means is that objects can be magnetized by "outside" forces like lightning or other magnetic objects around them. The heating process removes these distracting magnetic fields so the objects' true magnetism can be analyzed. It sounds like science fiction doesn't it?
First their magnetic fingerprint is taken, and then they are slightly demagnetized. The process is repeated several times; eventually all that is left is the baseline magnetic signal, she said. If the material is fired to about 500 degrees Celsius or more, the magnetic field will point to where magnetic north was located at the time.
I thought carbon dating was high tech but this beats it I think. And I don't know why I'm surprised to learn that magnetic north changes over time. After all, this planet doesn't act very sober as it swims drunkenly through space. All pagans know a little about this kind of thing already as the irregular movements of the planet make some of our holydays bounce around the calendar by a day or two every year. I just never considered how that affected the science of archaeology. I guess you do learn something new every day.