Tel Aviv — Albert Einstein considered the origin of the Earth’s magnetic field one of the five most important unsolved problems in physics. The 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 by some for the welfare of the biosphere.
But in a new study published in PNAS, Tel Aviv University, Hebrew University of Jerusalem, and University of California San Diego researchers find there is no reason for alarm: The Earth's geomagnetic field has been undulating for thousands of years. Data obtained from the analysis of well-dated Judean jar handles 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,” says Dr. Erez Ben-Yosefof 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.”
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," Dr. Ben-Yosef observes.
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 century BCE, providing accurate age estimates.
"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," said Dr. Ben-Yosef. "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."
Additional researchers: Prof. Oded Lipschits, TAU; Michael Millman, TAU; Dr. Ron Shaar, Hebrew University; Prof. Lisa Tauxe, UC San Diego.