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Albert Einstein considered the origin of Planet Earth’s magnetic field to be one of the five most important yet unsolved problems in physics.
The supposed weakening of the geomagnetic field, which extends from the planet’s core into outer space and was first recorded 180 years ago, has raised concern for the welfare of the biosphere and for life on Earth.
A new study by researchers from Tel Aviv University (TAU), Hebrew University of Jerusalem and University of California San Diego found no reason for alarm. The Earth’s geomagnetic field has been undulating for thousands of years, they say.
Data obtained from the analysis of ancient jar handles found in Judea provide information on changes in the strength of the geomagnetic field between the 8th and 2nd centuries BCE, indicating a fluctuating field that peaked during the 8th century BCE.
“The field strength of the 8th century BCE corroborates previous observations of our group, first published in 2009, of an unusually strong field in the early Iron Age. We call it the ‘Iron Age Spike,’ and it is the strongest field recorded in the last 100,000 years,” said Dr. Erez Ben-Yosef of TAU’s Institute of Archaeology, the study’s lead investigator.
“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,” he explained
Delving into Earth’s Inner Structure
“We can gain a clearer picture of the planet and its inner structure by better understanding proxies like the magnetic field, which reaches more than 1,800 miles deep into the liquid part of the Earth’s outer core,” Ben-Yosef observed.
The new research is based on a set of 67 ancient, heat-impacted Judean ceramic storage jar handles, which bear royal stamp impressions from the 8th to 2nd centuries BCE, providing accurate age estimates.
“The period spanned by the jars allowed us to procure data on the Earth’s magnetic field during that time — the Iron Age through the Hellenistic Period in Judea,” Ben-Yosef said. “The typology of the stamp impressions, which correspond to changes in the political entities ruling this area, provides excellent age estimates for the firing of these artifacts.”
To accurately measure the geomagnetic intensity, the researchers conducted experiments at the Paleomagnetic Laboratory of Scripps Institution of Oceanography (SIO), University of California San Diego, using laboratory-built paleomagnetic ovens and a superconducting magnetometer.
“Ceramics, baked clay, burned mud bricks, copper slag — almost anything that was heated and then cooled can become a recorder of the components of the magnetic field at the time of the event,” Ben-Yosef elaborated. “Ceramics have tiny minerals – magnetic ‘recorders’ – that save information about the magnetic field of the time the clay was in the kiln. The behavior of the magnetic field in the past can be studied by examining archaeological artifacts or geological material that were heated then cooled, such as lava.”
Using the Knowledge the Other Way Around
Observed changes in the geomagnetic field can, in turn, be used as an advanced dating method complementary to the radiocarbon dating, according to Ben-Yosef. “The improved Levantine archaeomagnetic record can be used to date pottery and other heat-impacted archaeological materials whose date is unknown,” he said.
“Both archaeologists and Earth scientists benefit from this. The new data can improve geophysical models – core-mantle interactions, cosmogenic processes and more – as well as provide an excellent, accurate dating reference for archaeological artefacts,” he added.
The researchers are working on enhancing the archaeomagnetic database for the Levant, one of the most archaeologically-rich regions on the planet, to better understand the geomagnetic field and establish a robust dating reference.