SCIENTIFIC EDUCATIONAL CENTER science idea

The results of a new study by the University of Liverpool provide additional evidence for an approximately 200-million-year cycle of the strength of the Earth's magnetic field.

Scientists performed thermal and microwave paleomagnetic analysis of rock samples from ancient lava flows in Eastern Scotland to measure the strength of the geomagnetic field at key time periods in the practical absence of previously 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 the previously identified period of low magnetic field strength, which began about 120 million years ago. The researchers called this period the " Middle Paleozoic Dipole Low Level (MPDL)".

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 in a previous study conducted in 2012. However, at that time there was no reliable data on the field strength available until 300 million years ago, so the new study fills an important time gap.

The Earth's magnetic field protects the planet from huge bursts of deadly solar radiation. It is not completely stable in strength and direction, both in time and in space, and has the ability to completely flip or change with significant consequences.

Deciphering the changes in the past intensity of the geomagnetic field is important because it indicates changes in the deep Earth processes over hundreds of millions of years and may provide a clue to how it may fluctuate, flip or unfold in the future.

A weak field is also important for life on our planet. A recent study showed that the mass extinction in the Devonian-Carboniferous period is associated with increased UV-B levels, about the same as the weakest field measurements of MPDL.

Liverpool paleomagnetist and lead author of the paper Louise Hawkins said: "This comprehensive magnetic analysis of the Strathmore and Kinghorn lava flows was key to filling in the period leading up to the Keeman Superchron, the period when the geomagnetic poles are stable."

"This data set complements other studies that we have been working on over the past few years together with our colleagues from Moscow and Alberta."

“Our results, when viewed together with existing data sets, confirm the existence of an approximately 200-million-year cycle of the Earth's magnetic field strength associated with deep Earth processes. Since almost all of our evidence for processes in the Earth's interior is constantly being destroyed by plate tectonics, preserving this signal for the depths of the Earth is extremely valuable as one of the few limitations that we have.”

Author: Roman Grigoriev

The article "The intensity of the Earth's magnetic field: evidence of a dipole minimum in the Middle Paleozoic" is published in the Proceedings of the National Academy of Sciences.

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