Further evidence of a 200 million year cycle for the Earth’s magnetic field

The results of a new study from the University of Liverpool provide further evidence of a cycle of around 200 million years in the strength of the Earth’s magnetic field.

Researchers performed thermal and microwave paleomagnetic analysis (a technique unique to the University of Liverpool) on rock samples from ancient lava flows in eastern Scotland to measure the strength of the geomagnetic field during key periods with almost no pre-existing reliable data. The study also analyzed the reliability of all measurements of samples from 200 to 500 million years ago, collected over the past 80 years.

They found that between 332 and 416 million years ago, the strength of the geomagnetic field preserved in these rocks was less than a quarter of what it is today, and similar to a previously identified period of low magnetic field strength. which started about 120 million years ago. . Researchers coined this period as “Middle Paleozoic Dipolar Depression (MPDL)”.

Posted in Proceedings of the National Academy of Sciences, the study supports the theory that the strength of the Earth’s magnetic field is cyclical and weakens every 200 million years, an idea proposed by a previous study conducted by Liverpool in 2012. One of the limitations to the era was the lack of reliable field strength data available before 300 million years ago, so this new study fills a significant time gap.

Earth’s magnetic field protects the planet from huge explosions of deadly solar radiation. It is not completely stable in strength and direction, both in time and space, and has the ability to turn around or completely reverse with substantial implications.

It is important to decipher the variations in the strength of the geomagnetic field in the past, as this indicates changes in deep earth processes over hundreds of millions of years and could provide clues as to how it might fluctuate, tip over. or reverse in the future.

A weak field also has implications for life on our planet. A recent study suggested that Devonian-Carboniferous mass extinction is related to high UV-B levels, roughly the same as weaker MPDL field measurements.

Liverpool paleomagnetist and lead author Dr Louise Hawkins said: “This comprehensive magnetic analysis of the Strathmore and Kinghorn lava flows was essential in bridging the lead-up to the Kiman Superchron, a period when the Geomagnetic poles are stable and do not return for about 50 million years.

“This dataset complements other studies we have been working on in recent years, alongside our colleagues in Moscow and Alberta, which fall between the ages of these two places.

“Our results, when viewed with existing datasets, support the existence of an approximately 200 million year cycle in the strength of the Earth’s magnetic field related to deep Earth processes. Like almost all of our evidence. As processes inside the Earth are constantly destroyed by plate tectonics, preserving this signal for the depths of the Earth is extremely valuable as one of the few constraints we have.

“Our results also confirm that a weak magnetic field is associated with pole reversals, while the field is generally strong during a Superchron, which is important because it has proven to be nearly impossible to improve the reversal record. before about 300 million years. “

The article, “Earth’s Magnetic Field Intensity: Evidence of a Low Middle Paleozoic Dipole”, is published in Proceedings of the National Academy of Sciences.