The behavior of the Earth’s magnetic field that emanates from the planet’s deep interior but extends far out into space and has existed for more than three and a half billion years but fluctuates daily, is one of the most enigmatic topics in physics. But now, clues can be found by detecting its intangible and mostly invisible behavior in the past, in geology and archaeological artifacts,” says Dr. Erez Ben-Yosef of Tel Aviv University.
Our planet’s history includes geomagnetic reversals that occur a few times every million years on average. However, the interval between reversals is very irregular and can range up to tens of millions of years. There can also be temporary and incomplete reversals, known as events and excursions, in which the magnetic poles move away from the geographic poles – perhaps even crossing the equator – before returning back to their original locations.
Many doomsday theorists have tried to take this natural geological occurrence and suggest it could lead to Earth’s destruction. But would there be any dramatic effects? NASA’s answer, from recent geologic and fossil records from hundreds of past magnetic polarity reversals, seems to be ‘no.’ But the magnetic north pole is moving faster now, actually, as scientists estimate the pole is migrating northward about 40 miles per year, as opposed to about 10 miles per year in the early 20th century.
The international team led by Ben-Yosef concludes that there was a massive geomagnetic spike in the late 8th century B.C.E.
“We call it the ‘Iron Age Spike,’ and it is the strongest field recorded in the last 100,000 years,” Ben-Yosef says. “This new finding puts the recent decline in the field’s strength into context. Apparently, this is not a unique phenomenon – the field has often weakened and recovered over the last millennia.” The Iron Age Spike brought the magnetic field to its strongest intensity in at least 100,000 years and maybe in history altogether,” adds Ben-Yosef.
What could have caused such a violent spike, to 2.5 times the present intensity, in the magnetic field? We have no clue, only that it happened thousands of kilometers beneath our feet, in the molten iron area of the planet. “If we have a spike, it was probably caused by turbulence or other phenomenon deep in the earth,” Ben-Yosef says.
Following the 8th century spike the magnetic field weakened rapidly, losing 27% of its strength over 30 years. Then it waned from the 6th to the 2nd century B.C.E., spanning the Iron Age through the Hellenistic era in Judea.
Since the magnetic sphere is clearly important to our existence, it’s critical to know what is causing it to constantly change in intensity and direction.
For 600 years, from the late 8th to the 2nd century B.C.E., these ceramic jars with very distinctive handles bearing impressions of royal stamps were manufactured in and around Judahite Jerusalem. The type of stamp changed with time according to the political situation.
Understanding this story about ancient Hebrews, the kings’ jars and the planet’s core involves knowing that materials that have been heated and then cooled, from igneous rocks to fired clay to burned mud bricks to bronze chickens, acquire “thermoremanent magnetization.” In other words, they become weakly magnetized in the direction and intensity of the earth’s magnetic field.
By analyzing the thermoremanent magnetization of a Judahite jar handlescgeophysicists can deduce the direction and magnitude of the Earth’s magnetic field in prehistory. The 67 ancient pottery handles, are a record of geomagnetic intensity at that time.