By analyzing the orientations of the metals in a set of these jar
handles with dates from 750 to 150 BCE, the scientists were able to see
traces of the geomagnetic field's behavior. What they found was
startling. Sometime late in the 8th century BCE, there was a rapid fluctuation in the field's intensity over a period of about 30 years—first the intensity increased to over 20 percent of baseline, then plunged to 27 percent under baseline. Though the overall trend at that
time was a gradual decline in the fields' intensity similar to what we
see today, this spike was basically off the charts.
Writing in The New Yorker, Lawrence University geologist Marcia Bjornerud points out
that this geomagnetic spike is far bigger than anything geoscientists
had believed possible. "Both the height and the sharpness of the spike
they recount push up against the limits of what some geophysicists think
Earth’s outer core is capable of doing," she explains. "If the
eighth-century-BC geomagnetic jeté is real, models for the generation of
the magnetic field need significant revision."
And, to make it even more interesting,
The researchers note that this geomagnetic spike is similar to another
that occurred in the 10th century BCE. Data from the 10th century spike
and this 8th century one indicate that such events were probably
localized, not global. That said, they write that "the exact geographic
expanse of this phenomenon has yet to be investigated, and the fact that
these are very short-lived features that can be easily missed suggests
that there is much more to discover."
And they note that such a spike today could mean disaster for the area where it happens.