In ancient Judea, potters often created jars big enough to hold wine or olive oil and sent them to kings as tax payment.
Even as rulers came and went over the years, potters kept making the same ceramic jars. Little did they know, however, that their creations would someday contribute to science.
Indeed, these 3,000-year-old ancient jars provide some clues into the strength of Earth's magnetic field, a new study in Israel revealed. It's as if the jars themselves hold records of the waning and fluctuating strength of the magnetic field over time, researchers said.
Earth's Magnetic Field
Earth is surrounded by a magnetic field generated by iron in its core. This magnetic field protects the planet from hazardous levels of high-energy particles called cosmic radiation.
In the past, scientists have found that Earth has lost at least 10 percent of the strength of its magnetic field. They are concerned that the planet might lose its magnetic field entirely.
But archeologist Erez Ben-Yosef, one of the authors of the new study, said there is nothing to fear. The ancient clay jars may hold hope.
As potters continued to throw clay, the iron core that was moving beneath them thousands of miles below attracted the tiny fragments of magnetic minerals that were in the clay.
As the jars were heated and cooled, the minerals swiveled and froze like tiny compasses that respond to the strength and direction of the magnetic field at the particular moment.
"It's kind of like a tape recorder," said Ben-Yosef.
Researchers said political instability in the region also contributed in the recording, because as the jars were stamped with different royal seals over different periods, the records were narrowed down to a window of about 30 years.
For instance, archeologists know that Assyrians destroyed Judah or Judea in 701 B.C., causing the tax jar seal to change. Because of this, Ben-Yosef and his colleagues can pinpoint what happened to the Earth's magnetic field during 730 B.C.E. to 700 B.C.E.
Weakened Magnetic Field?
Ben-Yosef and his team studied about 67 jar handles from the late 8th century B.C. to the late 2nd century B.C. and found that during this time, the magnetic field of Earth became "choppier" than expected.
Based on the late 8th century BC jars, the core of the Earth went "crazy," and the intensity of the magnetic field doubled compared to what it is today. It may have been the strongest intensity in 10,000 years, researchers said.
Afterwards, the core weakened during 732 B.C.E., losing the intensity in just 30 years. Still, Ben-Yosef said massive fluctuations such as this are not a cause for concern. He said fluctuations are the norm for Earth's magnetic field, and not a harbinger of destruction.
Details of the study were featured in the journal Proceedings of the National Academy of Sciences.