Researchers working in Israel have used ancient clay pots to create one of the most detailed reconstructions in the history of Earth’s historical magnetic field, according to a new study in the journal Proceedings of the National Academy of Sciences.
Over the last 2,000 years, Earth’s magnetic field has weakened by roughly 10 percent. That drop, combined with the fact that the magnetic north pole has wandered over 900 miles since 1990, has caused some scientists to wonder if our planet is at the beginning of a periodic flip, in which north becomes south and south becomes north.
In the past, scientists have tracked such shifts by looking at the fossilized remnants of the magnetic field that sit on the bottom of the sea. This is possible because molten, iron-laden minerals line up with the field and get locked into its orientation upon cooling, The Christian Science Monitor reports.
However, while that data goes back 175 million years, intermediate trends are much harder to track.
In the new study, the team sheds some light on more recent patterns by looking at magnetic records baked into ancient ceramics. Like seafloor lava vents, fired clay pots preserve a record of the magnetic field as they cool.
Though such artifacts are typically hard to date, many of the jugs discovered near Jerusalem have stamps on their handles that can be matched to different periods between the 8th to 2nd century B.C.
“This was the system of the king in Jerusalem to be able to collect tax efficiently,” lead author Erez Ben-Yosef, an archaeologist at Tel Aviv University, told Live Science. “We are actually benefiting from a good bureaucratic system, the ancient IRS.”
These stamps helped the team create an accurate record of geomagnetic field intensity that revealed that the Earth’s magnetic force is constantly shifting. They identified a 50 percent spike in the late 8th century B.C. that raised the field to nearly twice what it is today. Then, it lost nearly a third of its strength over the next three decades.
Though those shifts did not have an effect on the ancient Judeans, they would create problems for modern satellites. However, scientists believe that the chaotic nature of the fluctuations mean that the recent shift in magnetic power is a natural shift and should not be cause for concern.
Even so, the findings are important because they raise many questions about the fluid dynamics at the Earth’s core that govern the magnetic field.
If the research is correct, the intensity of the ancient spike shows that the Earth may shift more than previously believed. This would then mean scientists would have to revisit — and possibly update — current geophysical models. A better understanding of the global phenomenon could enable researchers to predict future field fluctuations and give them a new idea of how magnetic shifts occur.
“When dealing with such large-scale phenomena, we don’t usually think it can occur within a few decades. We usually think it would take thousands or tens of thousands of years,” said Steven Forman, a geologist at Baylor University, who was not involved in the study, according to NPR.