About 3,000 years ago, a potter near Jerusalem made a big jar. It was meant to hold olive oil or wine or something else valuable enough to send to the king as a tax payment. The jar's handles were stamped with a royal seal, and the pot went into the kiln.
[...] All those years ago, as potters continued to throw clay, the molten iron that was rotating deep below them tugged at tiny bits of magnetic minerals embedded in the potters' clay. As the jars were heated in the kiln and then subsequently cooled, those minerals swiveled and froze into place like tiny compasses, responding to the direction and strength of the Earth's magnetic field at that very moment.
"It's kind of like a tape recorder," [Erez] Ben-Yosef says.
[...] When Ben-Yosef and his colleagues studied 67 jar handles spanning from the late 8th century B.C. to the late 2nd century B.C., they found that the Earth's magnetic activity has been a lot choppier than people expected.
Ben-Yosef et al. Six centuries of geomagnetic intensity variations recorded by royal Judean stamped jar handles [PNAS (2017) - Early Edition] DOI: 10.1073/pnas.1615797114
(Score: 1) by Linatux on Friday February 24 2017, @04:03AM
Any samples that have been re-heated (when a city is destroyed by fire) may have been reset?
(Score: 2, Informative) by Linatux on Friday February 24 2017, @04:09AM
Learn something new every day!
1043K or about 770C - probably too hot for your average loot & pillage fire.
(Score: 2) by linkdude64 on Friday February 24 2017, @04:19PM
I just learned the facts about magnetism and heat recently for a more modern application - wanting to apply magnets to my oil filters to attract steel shavings smaller than filters can trap. Obviously, engines get hot.
Turns out there's already a commercial solution (which I won't name or link) but thought you might be interested, in any case.
(Score: 2) by LoRdTAW on Friday February 24 2017, @04:24PM
Or a magnetic drain plug.
(Score: 2) by linkdude64 on Friday February 24 2017, @05:28PM
Definitely a good suggestion, and I fortunately already have one! I just want added measures as the vehicle is still running well, but is over 250k miles. The surface area available on the drain plug magnet isn't a lot compared with a small array flat-face magnets. See pic of used filter - quite a bit more material than could be caught on the tip of a plug.
https://ixquick-proxy.com/do/spg/show_picture.pl?l=english&rais=1&oiu=http%3A%2F%2F67-72chevytrucks.com%2Fvboard%2Fattachment.php%3Fattachmentid%3D833473%26amp%3Bstc%3D1%26amp%3Bd%3D1322291828&sp=fb70e827f4f5ce414bac9a60b90aa020 [ixquick-proxy.com]