Relax, Earthlings: Analysis of clay pots around 3,000 years old that had been made in and around Jerusalem indicates that if the end is nigh, it won't be because of Earth's magnetic field.
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The discoveries debunk scare scenarios that the magnetic field is irreversibly diminishing to zero and the planet will be destroyed by cosmic radiation. Yes, the field has been diminishing, but research has proven that it can fluctuate both mightily, and fast, so violent fluctuation should not send us into a panic.
The magnetic field is of intense interest to physicists, because they don't understand it but suspect the earth's magnetic pole is about to flip. It is of intense interest to biologists, who have been listing the myriad ways it affects behavior, and also, because they suspect correlation between magnetic pole flips and mass extinctions.
It is of interest to all scientists, really, because of the notion that the magnetic field protects life on earth from deadly mutagenic cosmic radiation; and it is of keen interest to archaeologists, of all people.
Why archaeologists? If we know exactly what intensity the field was at this or that date, and find the "fingerprint" of the magnetic field in pottery, we can date that pottery very accurately, archaeologist Dr. Erez Ben-Yosef of Tel Aviv University explained to Haaretz.
Conversely in this case, pieces of pottery whose date is exactly known have preserved a record of the geomagnetic field over six centuries during the era of the Judean kingdoms. "Ceramics have tiny minerals – magnetic ‘recorders’ – that save information about the magnetic field of the time the clay was in the kiln," Ben-Yosef explains.
The pottery jars have also helped prove that there was an anomalous massive spike in the geomagnetic field in the late 8th century B.C.E. Following that, the magnetic field weakened rapidly, losing 27% of its strength over 30 years. Then it gently 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 would be nice to know what controls it – what is causing it to constantly change in intensity and direction (though complete flips are rare). We know its behavior is ruled by action in the planet's outer core, which lies as much as 2900 kilometers below our feet, but we don't know how.
"Its behavior remains one of the most enigmatic topics in physics, but clues can be found by detecting its behavior in the past, in geology and archaeological artifacts," says Ben-Yosef.
The Judahite jar habit
Conveniently, from the late 8th to the 2nd century B.C.E., meaning throughout 600 years, 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." They become weakly magnetized in the direction and intensity of the earth's magnetic field.
Analyzing the thermoremanent magnetization of a rock – or a Judahite jar handle – is how geophysicists can deduce the direction and magnitude of the Earth's magnetic field in prehistory.
Thus, the ancient pottery (67 handles, specifically) are a record of geomagnetic intensity in the Levant at that time, explains the team headed by Ben-Yosef, with TAU archaeologists Michael Millman and Oded Lipschits, earth scientist Ron Shaar of the Hebrew University of Jerusalem and geophysicist Lisa Tauxe of Scripps Institution of Oceanography in their paper published Tuesday in PNAS.
Their conclusion: There was a massive geomagnetic spike in the late 8th century B.C.E.
The Iron Age Spike
"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.”
In fact, adds Ben-Yosef, the Iron Age Spike brought the magnetic field to its strongest intensity in at least 100,000 years and maybe in history altogether. (In further fact, when the scientists first reported discovering the Iron Age Spike back in 2009, geophysicists pooh-poohed the result, thinking it too extreme to be likely.)
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.
By the way, the Judahite handles can tell us about changing intensity in the magnetic field, but not direction. In contrast to say a basalt flow, they were moved since their firing.
Measurements since the 1830s show that the magnetic field has been weakening. Some believe the planet is about to lose its magnetic shield altogether, which might in turn spell an end of life on Earth. Others think the magnetic field is poised to reverse, or is already in the process (we don't even know that for sure).
Following this study and its proof that the field has fluctuated violently in the past, Tel Aviv University is of the opinion that if anything is going to doom the world, it isn't that.