Iron Age Potters Carefully Recorded Earth’s Magnetic Field — By Accident

Rae Ellen Bichell at NPR:

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.

Over the next 600 years, despite wars destructive enough to raze cities, potters in the area kept making ceramic tax jars, each one stamped with whatever seal represented the ruler du jour.

They didn't know it, but in the process, the ancient potters were not just upholding centuries of tax bureaucracy.

As a group of archaeologists and geophysicists wrote Monday in the journal PNAS, they were also creating a long-lasting record of activity some 2,000 miles beneath their feet. And that record is now yielding clues to a big mystery about this planet: how its magnetic field has changed over time.

More here.