Changes to Earth’s magnetic field recorded in 600-year-old Judean pottery

Posted: February 14, 2017 by oldbrew in innovation, research
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Kingdom of Judah [credit: IB Times]

Kingdom of Judah [credit: IB Times]


The ‘two Iron Age spikes’ in magnetism could be worth investigating further.

Ancient clay jar handles can act as a record of the Earth’s magnetic history, a new study finds, confirming evidence of sudden, sharp spikes in the strength of the field, as the IB Times reports.

Fragments of pottery were historically stamped with an emblem of the rulers of the Kingdom Judah, which encompassed Jerusalem and nearby areas. These jars were also marked by the state of the Earth’s geomagnetic field at its time of construction, offering researchers a unique chance to reconstruct the past of the Earth’s magnetic field.

The study is based on the technique of archaeomagnetism. Some minerals in clay are magnetic, and before they are heated they are aligned randomly. As the pottery is heated during the firing process, the magnetic particles tend to align with the Earth’s magnetic field. The stronger the magnetic field, the greater the degree of alignment in the magnetic minerals.

Using this method, archaeologists at Tel Aviv University in Israel were able to measure the geomagnetic field intensity in Judah from the 8th Century BCE to the 2nd Century BCE, publishing their results in a paper in the journal PNAS.

“The new record constitutes a substantial advance in our knowledge of past geomagnetic field variations in the southern Levant,” the authors write in the paper.

They used 67 ceramic jar handles that were clearly stamped with a royal seal, allowing them to put a relatively precise date on the age of the pottery.

They found that in the late 8th Century BCE there was large spike in intensity of the Earth’s magnetic field, and then a rapid decline of more than 20% of the strength of the field in just 30 years. After that, there was a much more gradual decline up until the 2nd Century BCE.

The measurement of the 8th Century BCE spike – one of two Iron Age spikes, the other happening about 200 years earlier – confirms previous research measuring such an anomaly.

“Both the 10th-century and 8th-century BCE spikes occurred during a time span of generally high field values worldwide, which appears to promote rapidly fluctuating and unstable fields,” the authors write.

They suggest that using dated pottery for further archaeomagnetic research could be a promising way to approach the study of these magnetic anomalies.

Source: Changes to Earth’s magnetic field recorded in 600-year-old Judean pottery | IB Times

Comments
  1. oldbrew says:

    Re the ‘8th century BCE’ spike, the abstract says:
    The rate of change during this “geomagnetic spike”…is further constrained by the new data, which indicate an extremely rapid weakening of the field (losing ∼27% of its strength over ca. 30 y).

    Obviously 30 years is indeed ‘extremely rapid’ for this type of event.

  2. E.M.Smith says:

    @Oldbrew:

    It depends on what you mean by “these kinds of events”.

    If a global shift, yes, but local magnetic jerk or excursion is commonly faster.

    The magnetic field isn’t uniform, especially when changing, and loops of magnetism can pop up in a place, then move or sink back below the surface. Remember they are only measuring one tiny little spot.

  3. oldbrew says:

    EM – re ‘loops of magnetism can pop up in a place, then move or sink back below the surface’

    On Earth?

  4. oldbrew says:

    Mysterious ‘geomagnetic spike’ 3,000 years ago challenges our understanding of the Earth’s interior
    November 8, 2017

    Until very recently, the Jordanian spike was the only such event ever observed. However, there is now tantalising new evidence for another spike-like feature in Texas, also around 1000BC. Our understanding of what spikes should look like, how they change in time, and how they relate to the motion of the liquid iron in Earth’s core are also improving rapidly.

    Coupled with numerical simulations that model the dynamics of Earth’s core, it may soon be possible to make the first predictions of how often spikes occur and the most likely locations where they could have occurred in the past (and may occur in the future). It could turn out that they are more common than we think.

    http://theconversation.com/mysterious-geomagnetic-spike-3-000-years-ago-challenges-our-understanding-of-the-earths-interior-86638

  5. p.g.sharrow says:

    @oldbrew; these may be localized spikes. The Earths magnetic field is the sum total of all the planets local magnetic fields. The local fields are influenced by the Lavalamp like movements of materials between the core and crust. Kind of chicken or egg conditions as material movements cause fields / fields cause movements in material. Stronger fields cause crystal lattice structure coagulation weakening fields cause liquidification. Solar fields acting on spinning semi-liquid planetary body influence the creation of these fields. Lots of moving parts to ascribe cause and effect…pg

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