The strength and direction of the Earth’s magnetic field have changed greatly over the millennia. Scientists are eager to study their past patterns to find out how the field might change in the future, a rather vital field of research, as this magnetic shield protects us from harmful cosmic radiation.
However, instruments capable of directly measuring the Earth’s magnetic field have only existed for about 200 years. Therefore, we must resort to other methods to trace them back in time, including, in a new study, artifacts recovered from a site in Jordan, dated about 8,000-10,000 years ago (the Neolithic or New Age of Stone).
These items, including the pottery and burnt flint used to make other tools, are special because their creation involved subjecting them to extremely high temperatures.
That process of warming and subsequent cooling caused certain minerals and crystals in the artifacts to catch a ‘frozen’ record of what the Earth’s magnetic field was like at the time, a phenomenon known as residual or remnant magnetization.
“This is the first time burned flints from prehistoric sites have been used to reconstruct the magnetic field from its time period,” says archaeologist Erez Ben-Yosef of Tel Aviv University in Israel.
“Working with this material expands the possibilities of research tens of thousands of years ago, as humans used flint tools for a very long period of time before the invention of ceramics.”
The excavation site in Jordan. (Thomas E. Levy)
The researchers examined a total of 129 different items, based on previous work evaluating the feasibility of using flint fragments as a guide for magnetic field strength, which will be incredibly useful for future studies.
What the team found was a drop in the strength of the magnetic field during the time the artifacts were used, followed by a recovery over a few hundred years (almost nothing in the grand scheme). of the history of the planet).
Because the Earth’s magnetic field is weakening over time (a potential source of concern), it is helpful to know that this has happened before and does not necessarily mean that our protective bubble will disappear in the next few centuries.
“The findings of our study can be reassuring: this has happened in the past,” says geophysicist Lisa Tauxe of the Scripps Institution of Oceanography.
“About 7,600 years ago, the strength of the magnetic field was even lower than it is today, but in about 600 years it gained strength and rose again to high levels.”
Our planet’s magnetic field is believed to be generated by convection currents created as molten iron and nickel circulate in the Earth’s outer core, about 3,000 kilometers (1,864 miles) underground, but there is not much more. that we are safe.
Some of the unanswered questions about this great phenomenon focus on how exactly the magnetic field could be connected to the processes of the Earth’s atmosphere and climate change and how they influence each other.
And while geological studies allow us to go back further in terms of tracking changes in the Earth’s magnetism, they do not offer the accuracy in terms of time that archaeological analysis does, as this latest study demonstrates.
“The essence and origins of the magnetic field have remained largely unresolved. In our research, we have tried to open a peephole to this great enigma,” says Ben-Yosef.
The research has been published in PNAS.