Researchers from the University of California, Israel’s Tel Aviv University and the Hebrew University of Jerusalem have logged the strength of Earth’s magnetic field over a 600-year-long period, using jar handles dating back to ancient times. By analyzing the iron oxide particles in these artifacts, the scientists have successfully determined the planet’s geomagnetic field over the course of several centuries.
Recently published in the Proceedings of the National Academy of Sciences (PNAS) journal, the research adopts a new and innovative approach to study the changes in Earth’s magnetic field intensity through history. In case you are wondering, geomagnetic field is what protects our planet and everything on it from harsh solar winds and cosmic radiation. Speaking about the study, Tel Aviv University’s Dr. Erez Ben-Yosef said:
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.
As revealed by the team, the ancient jars from Israel’s Ramat Rahel were fashioned out of clay, containing iron oxide particles that in turn serve as an important measuring device for the Earth’s magnetic field strength. Thanks to this geomagnetic field, the alignment of these molecules gets fixed while the clay is still pliable, thus causing them to be sort of frozen in place following the firing process. Ben-Yosef added:
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. 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.
For the research, the team examined as many as 67 Judean jar handles from periods between 8th and 2nd century BC. Each of these artifacts was debossed with the royal stamp and other inscriptions for tax purposes, making the task of dating them relatively straight-forward. Once the age of the handles was determined, the scientists went ahead and analyzed the embedded iron oxide particles using lab-built paleomagnetic ovens as well as a superconducting magnetometer. Ben-Yosef explained:
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. 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.
The research has in turn uncovered some fascinating details about the planet’s geomagnetic field. For instance, the experiments point to a gradual, yet steady, decrease in field strength over the period of six centuries. Interspersed between them are occasional spikes and drops. Towards the end of the 8th century BC, the study reveals, Earth’s magnetic strength spiked suddenly, and decreased significantly soon afterward losing nearly 27-percent of this average intensity. The team went on to state:
The field strength of the 8th century BC 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. 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 addition to enhancing our understanding of geomagnetic field and the cause behind its fluctuations, the ingenious methodology could serve as an advanced dating technique, similar to radiocarbon dating. At present, the team is working to make expand the archaeomagnetic database for the historically-rich region of Levant.Dr. Ben-Yosef is of the opinion:
The improved Levantine archaeomagnetic record can be used to date pottery and other heat-impacted archaeological materials whose date is unknown. 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 artifacts.
Source: Tel Aviv University / Images Credit: Oded Lipschits