Neolithic stone reveals ancient secret of magnetism

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Reach the cosmos with invisible tendrils, the magnetism is both worldly and worldly.

These forces can pin a photo on your fridge or even rise up from the Earth’s poles to fight against the solar wind, and now a new study published in the journal Proceedings of the National Academy of Sciences shows that magnetism can also help us study the past.

Like fingerprints left on glass, pieces of clay or stone retain in them the memory of the terrestrial magnetism of a long time ago. And now scientists have found a way to reveal these secrets inside pieces of flint, one of the most common materials in history. This includes the oldest magnetic intensity data from the Levant region to date.

Lisa Ratee is professor of paleomagnetics at the University of California at San Diego and co-author of the new study. In addition to helping future researchers date historic sites in the Levant, studying the magnetism of these materials may also help researchers study what Ratee calls a “roller coaster” of magnetic activity on ancient Earth specific to the Levant region, the location of present-day Jordan.

“Our oldest specimens suggest field strengths of around two-thirds of our current field,” says Ratee Reverse. “Then the field grew until about 3,000 years ago, when it was about twice as large as it is today. Since then it has fallen on a roller coaster ride to the terrain today.

This roller coaster ride is known to scientists as the “Levantine Iron Age Anomaly”. Studying such magnetic events may even help us in our own climate change crusade, other research has suggested.

A photo of one of the team’s archaeological sites – Wadi Fidan 01 – in the Arabah Valley, Jordan.Thomas E. Levy

What’s new – While the study of ancient magnetism may not be a household name like carbon dating, Ratee says the technique is far from new. In the past, it was mainly used to study pieces of pottery. This is because pottery is fired at temperatures high enough to take this electromagnetic imprint – or “residual thermal magnetization”.

“When something cools in a magnetic field, it becomes magnetic with a force proportional to the field in which it has cooled,” says Ratee.

However, relying on pottery shards as the sole source of RMR can be uncertain, especially when trying to explore pre-pottery civilizations. That is why Ratee and his colleagues instead focused on a more ubiquitous material: flint.

While flint was not always heated by ancient civilizations, it was sometimes heated to make it easier to break and form specific shapes, like the tip of a spear.Shutterstock

Typically, flint would not be considered useful at all, Ratee says, because it is not always heated before being used as pottery. However, in this study, they developed a method to first determine whether or not flint samples were fired, and then applied the same analysis typically used on pottery to study its magnetism.

Ratee says this new approach means the team does not “have to waste their time in the future on flints that have never been fired.”

Why is this important – Incorporating flint into the catalog of paleomagnetism could help scientists not only better study the Levantine anomaly, but potentially even better understand the life of these civilizations in general, including their way of eating.

These sites are “important for understanding a number of issues in global archeology,” write the authors. “Including the origins of the village as a type of settlement, the domestication of plants and animals and the rise of the Mediterranean diet.”

Pottery is a great source for paleomagnetic research, but it tells us nothing about pre-pottery societies. Focusing on the flint instead might change that.Thomas Barwick / DigitalVision / Getty Images

How they did it – In their analysis, the team examined 129 flint samples from archaeological sites across modern Jordan dating between 7752 and 5069 BCE.

To determine the intensity of their magnetism, they used something called the IZZI protocol which essentially requires heating samples and comparing the strength of their magnetic fields with the current magnetism of the Earth.

By comparing the magnetism of these samples to known levels of magnetism throughout history, this technique can then be used in the same way as carbon dating.

And after – With the door now open to the use of flint worldwide as a record of ancient magnetism, the next steps in this research will be to build a more solid idea of ​​how magnetism has changed in other parts of the world, Ratee explains.

“In the Middle East, we have a really good idea of ​​what the estate has done in the past,” says Ratee. “The archaeomagnetic community is working to improve records around the world so that they can be applied with increasing confidence elsewhere.”

Ratee’s focus is initially on the Southwestern United States and Southeast Asia.

Abstract: The limitation of the secular variation of the strength of the Earth’s magnetic field in the past is fundamental to understanding the short-term processes of geodynamics. Such records are also a powerful and independent dating tool for archaeological sites and geological formations. In this study, we present 11 robust archaeointensity results from pre-pottery to Jordanian Neolithic pottery that are based on clay and flint (chert) artifacts. Two of these results constitute the oldest archaeointensity data for the entire Levant, ancient Egypt, Turkey and Mesopotamia, extending the archaeomagnetic reference curve for the Holocene. Virtual Axial Dipole Moments (VADM) show that the Earth’s magnetic field in the southern Levant was weak (about two-thirds of the current field) around 7600 BCE, regaining strength to a level higher than the current field around 7000 BCE. , and gradually weakening again around 5200 BCE. In addition, convincing results obtained from burnt flint demonstrate the potential of this very common material, yet rarely used, in archaeomagnetic research, in particular for prehistoric periods ranging from the first use of fire to the invention of pottery.


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