A recent article published by arstechnica.com about the electromagnetism of ancient jar handles in the Middle East struck a familiar chord. The piece cites a paper from the Proceedings of the National Academy of Sciences that reveals how broken pottery remains, uncovered in what was once the Kingdom of Judah and dating from the 8th century BCE, have yielded new information about the magnetic field surrounding the Earth. It is the magnetism part that caught my attention.
Though shattered and timeworn, scientists have discovered that the iron oxide in two millennium old clay jar handles, the thickest part of the ceramic containers, still retains the geomagnetic fingerprint of the local environment from long ago. That’s right. The iron oxide, a typical component of pottery clay, has naturally occurring magnetic tendencies including polarity. As arstechnica.com editor Annalee Newitz points out, when pottery is fired at temperatures of 770°C and above, the iron oxide’s magnetism fades out due to the Curie’s point. As the pottery cools, its magnetism naturally returns.
Now, researchers have discovered the well-worn ceramic handles located in Judah actually retained the magnetic properties of the surrounding local environment where the fragments cooled off after being fired. The same thing happens when molten lava cools down. But this time, experts found something else. After further analysis of the handles, scholars determined a huge “geomagnetic spike” happened in the area during ancient times. Newitz suggests the same kind of spike could wreak total havoc by modern standards. Sun spots and lightning storms are nothing compared to what could come about should such an event occur. But that is not what struck me about the story.
As if a kneejerk reaction, the item about the handles reminded me that the magnetic fingerprint of mineral aggregates on the west coast of Africa match up with rocks on the east coast of South America, which proved to be a major discovery in the field of plate tectonics. The rocks from each coast contained identifiable fluctuations regarding Earth’s magnetic poles. What does that have to do with the broken jar handles from Judah? In both cases, Earth’s magnetism held the key to understanding the past. Similarly, the clay handles have provided significant answers to questions about Earth’s magnetic field that are only beginning to be understood. Like they say, everything old becomes new again.
Video: Magnetism of the Earth – Kelly White/The Discovery Channel/YouTube.
Photos: A model of the magnetization of the earth’s crust – Michael Purucker/public domain/Creative Commons (CC); Iron oxide red yellowish – FK1954/own work/public domain/CC; Glowing lava flow – USGS/public domain/CC; usage of photos does not constitute endorsement.
Paul Wolfle has a B.A. in Geography from Hofstra University