The strength and direction of the earth Force field has changed a lot over thousands of years. Scientists are eager to study patterns in the past to see how the field might change in the future – an important area of research given that this magnetic shield protects us from harmful cosmic rays.
However, instruments that can measure Earth’s magnetic field directly have only been around for about 200 years. Therefore, we must turn to other methods to trace them further back in time – including, in a new study, artifacts recovered from a site in Jordan dating back about 8,000-10,000 years (Neolithic or Neolithic).
These items – including ceramic pottery and flint, which are used to make other tools – are special because they are exposed to very high temperatures in their manufacture.
This subsequent heating and cooling process produces certain minerals and crystals in the artifact capture record ‘frozen’ how the earth’s magnetic field was at that time, a phenomenon known as residual or remanent magnetization.
“This is the first time that roasted flint from a prehistoric site has been used to reconstruct magnetic fields from their time.” kata archaeologist Erez Ben-Yosef from Tel Aviv University in Israel.
“Working with this material expanded research opportunities for tens of thousands of years, because humans used flint tools for a very long time before the invention of ceramics.”
Archaeological sites in Jordan. (Thomas E. Levy)
The researchers examined a total of 129 different elements, which were built on previous job who evaluated the feasibility of using flint fragments as a guide to magnetic field strength – something that would be very useful for future studies.
What the team found was a decrease in the strength of the magnetic field during the artifact’s use, followed by a recovery over several hundred years (not long at all in the grand scheme of planetary history).
Since Earth’s magnetic field is currently weakening over time – a potential cause for concern – it is helpful to know that this has happened before, and does not mean that our protective bubble will disappear in the next few centuries.
“Our results are reassuring: this has happened in the past”, says geophysicist Lisa Tauxe dari Scripps Institution of Oceanography.
“About 7,600 years ago the strength of the magnetic field was lower than it is now, but in about 600 years it gained strength and rose again to a higher level.”
Our planet’s magnetic field is believed to be created by convection currents that occur as molten iron and nickel circulate in Earth’s outer core, some 3,000 kilometers (1,864 miles) underground – but we’re not sure about that.
Some of the unanswered questions about this massive phenomenon focus on how precisely the magnetic field is related to processes in Earth’s atmosphere and changes in Earth’s climate, and how they affect each other.
And while geological studies allow us to go further back in terms of tracking shifts in terrestrial magnetism, they don’t offer the timeliness that archaeological analysis provides – as this latest study shows.
“The nature and origin of the magnetic field is largely unclear. In our research, we have tried to open a peephole into this great mystery.” kata Ben-Yosef.
This study was published in PNAS.
–
