Uncover the secrets of the Earth’s magnetic field from 9,000-year-old recordings

International research by Tel Aviv University, the Istituto Nazionale di Geofisica e Vulcanologia, Rome, and the University of California at San Diego have uncovered findings regarding the magnetic field that prevailed in the Middle East there about 10,000 to 8,000 years ago. Researchers examined pottery and burnt flint from archaeological sites in Jordan, on which the magnetic field during this period was recorded. Information about the magnetic field in prehistoric times may affect our understanding of the magnetic field today, which shows a weakening trend that has raised concern among climatology and environmental researchers.

The research was conducted under the direction of Prof. Erez Ben-Yosef of the Department of Archeology and Ancient Cultures of the Near East Jacob M. Alkow at Tel Aviv University and Prof. Lisa Ratee, Head of the Paleomagnetic Laboratory at the Scripps Institution of Oceanography, in collaboration with other researchers from the University of California at San Diego, Rome and Jordan. The article was published in the journal PNAS.

Professor Ben-Yosef explains: “Albert Einstein characterized the planet’s magnetic field as one of the five greatest mysteries of modern physics. To date, we know a number of basic facts about this: The magnetic field is generated by processes that take place at a depth of about 3,000 km below the surface of the planet (for comparison, drilling deepest human reached a depth of only 20 km); it protects the planet from continuous bombardment by cosmic radiation and thus allows life as we know it to exist; it is volatile and its strength and direction are constantly changing, and it is linked to various phenomena in the atmosphere and the ecological system of the planet, including – perhaps – having some impact on the climate. Nevertheless, the essence and origins of the magnetic field have remained largely unresolved. In our research, we sought to open a peephole in this great enigma.

The researchers say that instruments for measuring the strength of the Earth’s magnetic field were first invented about 200 years ago. In order to examine the history of the field in previous periods, science is aided by archaeological and geological materials that recorded the properties of the field when they were heated to high temperatures. Magnetic information remains “frozen” (forever or until another heating event) in tiny crystals of ferromagnetic minerals, from which it can be extracted using a series of laboratory experiments. magnetism. Basalt from volcanic eruptions or ceramics fired in a kiln are materials frequently used for this type of experiment.

The great advantage of using archaeological material as opposed to geological material is temporal resolution: while in geology the dating is at best at the scale of thousands of years, in archeology artefacts and the magnetic field that they recorded can be dated to a resolution of hundreds. and sometimes even decades (and in specific cases, such as a known destruction event, even give an exact date). The obvious disadvantage of archeology is the young age of the artefacts involved: ceramics, which have been used for this purpose until now, were not invented until 8,500 years ago.

The current study is based on material from four archaeological sites in Wadi Feinan (Jordan), which have been dated (using carbon 14) to the Neolithic period – around 10,000 to 8,000 years ago – some of which predate the invention of ceramics. Researchers examined the magnetic field that was recorded in 129 objects found in these excavations, and this time, burnt flint tools were added to the ceramic shards.

Teacher. Ben-Yosef: “This is the first time that burnt flints from prehistoric sites have been used to reconstruct the magnetic field from their time. About a year ago, groundbreaking research at Hebrew University was published showing the feasibility of working with such materials, and we took a step forward in extracting geomagnetic information from very dated burnt flint. Working with this material expands the possibilities of research tens of thousands of years ago, as humans used flint tools for a very long time before the invention of ceramics. In addition, after we have gathered enough information about the changes in the geomagnetic field over time, we can use it to date the archaeological remains. “

Another important finding of this study is the strength of the magnetic field during the period examined. Archaeological artifacts have shown that at some point in the Neolithic period the field became very weak (among the lowest values ​​ever recorded in the last 10,000 years), but recovered and strengthened in a relatively short period of time.

According to Prof. Ratee, this observation is significant for us today: “In our time, since the start of measurements less than 200 years ago, we have witnessed a continuous reduction in the intensity of the field. This fact raises concerns that we may completely lose the magnetic field that protects us from cosmic radiation and, therefore, is essential for the existence of life on Earth. The conclusions of our study can be reassuring: this has happened in the past. About 7600 years ago the strength of the magnetic field was even weaker than it is today, but in about 600 years it has strengthened and reached high levels again.

Reference: “The strength of the Earth’s magnetic field from pre-pottery to Neolithic pottery, Jordan” by Anita Di Chiara, Lisa Ratee, Thomas E. Levy, Mohammad Najjar, Fabio Florindo and Erez Ben-Yosef, August 16, 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2100995118

The research was conducted with support from the Binational US-Israel Science Foundation, which encourages academic collaborations between universities in Israel and the United States. The researchers note that in this case, the collaboration was particularly critical to the success of the study because it relies on a close integration of methods from the fields of archeology and geophysics, and the information obtained is particularly relevant to these. two areas. disciplines.