Every couple million years, the Earth’s magnetic field does a complete 180, flipping the north and south magnetic poles and drastically weakening our natural defense against the sun’s geomagnetic storms. That wouldn’t be great for mankind, and there’s some evidence to suggest this flip might happen sooner rather than later. However, scientists uncovered some new evidence that says the magnetic field is just fluctuating, not disappearing.

That new evidence is some old jars.

These jars, ceramic and clay vessels from ancient Judea, are seriously old. Like, we’re talking 750 to 150 BCE old. Experts at Tel Aviv University were able to use fragments of the old jars to determine the how strong Earth’s magnetic field was at different points in history.

“Ceramics, baked clay, burned mud bricks, copper slag — almost anything that was heated and then cooled can become a recorder of the components of the magnetic field at the time of the event,” explains study lead author Dr. Erez Ben-Yosef in a release. “Ceramics have tiny minerals — magnetic ‘recorders’ — that save information about the magnetic field of the time the clay was in the kiln. The behavior of the magnetic field in the past can be studied by examining archaeological artifacts or geological material that were heated then cooled, such as lava,” he continued.

A jar.
A jar.

Ben-Yosef and his team studied 67 ancient, heat-impacted Judean ceramic storage jar handles. Each handle featured a royal stamp impression from different points spanning the 8th to 2nd century BCE, giving researchers a pretty accurate idea of exactly when the jars were made.

By studying these jars, researchers found that the magnetic field fluctuated quite a bit over the centuries without fully diminishing or flipping. The 8th Century — coincidently but fittingly called the Iron Age — was an especially strong field. Most of the time is was around 40 percent stronger than our modern field, with some fluctuations, but just before 700 BCE, the field’s strength skyrocketed and quickly plummeted in the following 30 years.

“This new finding puts the recent decline in the field’s strength into context,” Ben-Yosef said. “Apparently, this is not a unique phenomenon — the field has often weakened and recovered over the last millennia.”

The new findings will help archeologists use more accurate advanced dating techniques to determine the age of old artifacts, but the jars’ implications for geoscience are fascinating, especially given how drastic and sudden the 700 BCE spike was. The magnetic field might not be gearing towards a crazy polar shift. It’s just a lot more jumpy than we thought.

(Though, to be fair, a bonkers spike in the field’s strength like that again would totally mess up our electrical grid. Win some, lose some?)